A Natural and Vital Alliance: Immunity and Cancer

The human body has evolved a highly sophisticated network of surveillance and defense. This network, known as the immune system, protects us from external pathogens and continuously monitors our own cells for signs of abnormal transformation. It can recognize and eliminate cells that have acquired characteristics associated with malignancy. This phenomenon, known as tumor immune surveillance, represents one component of the body’s natural defenses against cancer.

When a normal cell undergoes genetic and epigenetic alterations that transform it into a cancer cell, it may acquire molecular features that distinguish it from healthy cells. Some of these can be recognized by the immune system as warning signals. This surveillance mechanism involves several cellular players, each with complementary and specialized functions.

Cytotoxic T lymphocytes can directly induce the death of target cells when they recognize appropriate antigenic peptides presented by major histocompatibility complex (MHC) class I molecules. Natural Killer (NK) cells, meanwhile, integrate activating and inhibitory signals to detect stressed, infected, or transformed cells. Reduced expression of certain MHC class I molecules may contribute to the recognition of “missing self,” although this is only one part of a broader regulatory process.

At the same time, macrophages and dendritic cells patrol tissues and can capture and process material derived from dying tumor cells. Dendritic cells are especially important because they present tumor-derived antigens to T lymphocytes, helping initiate and amplify an adaptive antitumor response.

The effectiveness of this surveillance varies considerably according to the nature of the cancer. In solid tumors, such as breast, lung, or colorectal cancer, the immune system faces the challenge of penetrating a tumor microenvironment that may be hostile to immune activity. Some tumors, such as melanoma, can carry a relatively high mutational burden, generating more neoantigens and potentially making them more visible to the immune system. Others, such as pancreatic cancer, often develop a profoundly immunosuppressive microenvironment that restricts the activity and access of immune cells.

Hematological cancers present a different scenario. Because they arise from cells of the blood-forming system and circulate through the bloodstream or lymphatic system, malignant cells may be accessible to immune cells in ways that differ from those in solid tumors. This distribution may facilitate interaction with immune cells, but it does not necessarily translate into effective immune control. Malignant cells can camouflage themselves, alter antigen presentation, or actively subvert immune mechanisms. Acute myeloid leukemia, for example, may impair mechanisms required for effective immune recognition. Similarly, some lymphomas develop microenvironments that recruit immunoregulatory cells and thereby weaken antitumor immunity.

The process of immune surveillance is evolutionary in nature and is described by what is known as the theory of cancer immunoediting. The cancer immunoediting model describes three interconnected phases that help explain how immune pressure can shape tumor evolution. During the initial elimination phase, the immune system destroys many emerging tumor cells, often without us ever becoming aware that they existed. When elimination is incomplete, an equilibrium phase may be established. At this stage, tumor growth is restrained without being completely eradicated, and malignant cells may remain clinically silent for prolonged periods.

Eventually, under the selective pressure exerted by the immune system, some tumor cells may acquire characteristics that allow them to evade immune attack, entering the escape phase. These mechanisms include reducing the expression or presentation of recognizable tumor antigens, upregulating inhibitory ligands such as PD-L1, and recruiting immunoregulatory cells into the tumor microenvironment.

Understanding these mechanisms has transformed cancer treatment. Immune checkpoint inhibitors, such as anti-PD-1, anti-PD-L1, or anti-CTLA-4 antibodies, interfere with inhibitory pathways that tumors can exploit to suppress effective T-cell responses. By releasing these molecular “brakes,” they can restore or enhance the antitumor activity of T lymphocytes in susceptible patients.

CAR-T cell therapy represents another major therapeutic advance. In many currently established approaches, a patient’s own T lymphocytes are genetically modified to recognize a defined antigen on cancer cells. Once reinfused, these living therapeutic cells can seek out and attack cells carrying their target.

A deeper understanding of the mechanisms underlying immune surveillance continues to open the door to increasingly precise and personalized therapeutic strategies. Combining immunotherapies with conventional treatments, developing therapeutic cancer vaccines, and finding ways to remodel the tumor microenvironment are all areas of intense research.

The human body has evolved a highly sophisticated system of surveillance and defense. Harnessing, strengthening, and directing this system represents an important area of modern oncology. As in many other areas of medicine, some of our most powerful therapeutic strategies may ultimately arise from understanding and intelligently using the body’s own defense mechanisms.

Cancer and the Natural Defenses of the Body: Cancer is an intricate disease that develops when cells in the body, instead of growing and dying in an orderly manner, begin to multiply abnormally and uncontrollably. This excessive growth can enable them to invade surrounding tissues and, in some cases, spread to distant organs through a process known as metastasis.

These changes in cellular behavior result from alterations in the genetic and epigenetic regulation of cells, particularly in pathways governing growth, cell division, differentiation, DNA repair, and programmed cell death.

Fortunately, the human body possesses sophisticated defenses against this internal threat. The immune system is a complex network of cells, tissues, organs, and signaling molecules whose primary function is to protect the body against infectious agents such as bacteria and viruses and, equally importantly, to detect and respond to damaged or abnormal cells, including cancer cells.

It acts as a sentinel, continuously monitoring the internal environment and responding to molecular signals that indicate infection, cellular stress, tissue damage, or malignant transformation.

However, the ability of this natural defense system to combat cancer is influenced by a fundamental process that accompanies life itself: aging.

As we grow older, many components of immune function undergo qualitative and quantitative changes. The ability to eliminate damaged or abnormal cells can become less effective, while other immune processes may become dysregulated. This forms part of a broader process of biological aging in which cells and tissues gradually accumulate molecular damage and changes in function.

Telomeres, protective structures at the ends of chromosomes, generally become shorter as cells undergo repeated division. Critically short telomeres can contribute to cellular senescence or genomic instability, although telomere biology is considerably more complex than a simple clock that determines aging.

Aging is also associated with increased oxidative stress, a state in which the production of reactive oxygen species exceeds the capacity of antioxidant systems to maintain redox balance. At the same time, many older adults experience chronic low-grade inflammation, often referred to as inflammaging.

Over time, oxidative stress, chronic inflammation, genomic instability, and other forms of cellular damage can contribute to tissue dysfunction and are associated with a broad range of age-related diseases, including several forms of cancer.

The immune system itself undergoes significant age-related changes, a process known as immunosenescence. These changes affect both innate and adaptive immunity. In some immune cells, alterations in migration, phagocytic activity, signaling, and antimicrobial function have been observed, while the adaptive immune system may experience changes in the diversity and responsiveness of lymphocyte populations.

Interestingly, some exceptionally healthy older adults, including centenarians, maintain aspects of immune function remarkably well. This suggests that immune function may provide valuable information about biological aging and healthspan, although no single immune parameter can serve as a definitive measure of biological age or a reliable predictor of longevity on its own.

This interconnection between aging and immunity raises an important possibility. Strategies associated with healthier aging may help preserve aspects of immune function, although their ability to prevent cancer through improved immune surveillance remains uncertain.

For example, geroprotective agents, substances being investigated for their potential to target fundamental mechanisms of aging, include metformin. Metformin has been associated in observational and experimental research with effects on several age-related pathways, but its role as a geroprotective treatment in healthy humans remains under investigation.

One of its best-known molecular targets is AMP-activated protein kinase (AMPK), a major cellular energy sensor that helps regulate energy production, nutrient availability, and metabolic adaptation. Metformin can influence AMPK signaling indirectly, although its biological effects are broader and context-dependent.

These pathways are involved in cellular stress responses, metabolism, and inflammatory signaling. The possibility that interventions targeting such mechanisms could simultaneously promote healthier aging and preserve immune competence is scientifically compelling, but it should not yet be presented as an established strategy for preventing cancer.

The Immune System: An Internal Defense Network: The immune system constitutes one of the body’s principal defense networks, dedicated to identifying and responding to substances, microorganisms, and cells that may represent a threat.

These targets are associated with antigens, molecular structures or fragments that can be recognized by immune receptors. Once an antigen is recognized in an appropriate context, the immune system can initiate a coordinated response designed to contain or eliminate the threat.

This system is composed of an extraordinary variety of specialized cells, each with a distinct role.

White blood cells, or leukocytes, are the principal cellular components of immune defense.

Phagocytes include macrophages and neutrophils. Dendritic cells also possess important mechanisms for capturing and processing extracellular material. Their functions include engulfing microorganisms, cellular debris, and other material and contributing to immune surveillance. Dendritic cells are particularly important because they process captured material and present antigen-derived peptides to T lymphocytes, thereby initiating and shaping adaptive immune responses.

T lymphocytes are highly specialized immune cells that mature and undergo selection in the thymus, acquiring the ability to distinguish between healthy self and potentially harmful targets.

• Cytotoxic T lymphocytes, or CD8+ T cells, can directly destroy virus-infected cells and cancer cells when they recognize appropriate antigenic peptides presented by MHC class I molecules.
• Helper T lymphocytes, or CD4+ T cells, coordinate immune responses through direct cellular interactions and the release of cytokines and other signaling molecules.
• Regulatory T lymphocytes are essential for maintaining immune tolerance and preventing excessive immune activation or attacks against healthy tissues. Their suppressive activity is vital for preventing autoimmune disease. At the same time, tumors can exploit regulatory mechanisms to weaken effective antitumor immunity.

B lymphocytes produce antibodies, Y-shaped proteins that bind specific molecular targets. Antibodies can neutralize pathogens, promote their elimination, or recruit other immune mechanisms. In cancer, antibodies directed against tumor-associated antigens can sometimes contribute to tumor-cell destruction.

Natural Killer, or NK, cells belong to the innate immune system and can rapidly recognize and destroy stressed, infected, or transformed cells without requiring prior exposure to a specific tumor antigen. Their activity is influenced by the balance between activating signals and inhibitory signals associated with normal cellular identity.

Key molecules

• Antigens are molecular structures or fragments recognized by immune receptors. In cancer, tumor cells may express tumor-associated antigens or tumor-specific antigens, including neoantigens generated by tumor-specific mutations.
• Cytokines are signaling proteins that regulate the development, activation, migration, and function of immune cells. Important examples include interferon-gamma (IFN-γ) and numerous interleukins.

The key to immune-system function lies in its ability to distinguish self from potentially harmful or abnormal targets. T lymphocytes use highly specific receptors to recognize peptide antigens presented by other cells, particularly through major histocompatibility complex molecules.

When an antigen is recognized in an appropriate immunological context, a cascade of cellular and molecular events can be initiated. The immune system also possesses immune memory, enabling certain lymphocyte populations to respond more rapidly and effectively when they encounter a previously recognized antigen again.

Despite this sophisticated capacity for recognition and attack, a fundamental paradox exists in the relationship between immunity and cancer.

Mechanisms of immune tolerance are essential for preventing the immune system from mistakenly attacking healthy tissues. Regulatory T cells and multiple other inhibitory pathways help maintain this delicate balance. Indeed, the immune system evolved primarily to protect the organism against infections and other threats, while its capacity to recognize and control malignant transformation is a complex extension of these broader functions.

The challenge is that cancer cells can exploit precisely these mechanisms.

By activating inhibitory pathways that normally protect healthy tissues from excessive immune attack, tumor cells can suppress effective T-cell responses and evade destruction. Thus, mechanisms that are indispensable for protecting the body can, under certain circumstances, become a shield for malignancy.

Table 1. Key Components of the Immune System and Their Role in Tumor Surveillance

Cancer Immunoediting: A Dynamic Relationship: Immune surveillance refers to the capacity of the immune system to recognize and eliminate some emerging tumor cells before they become clinically apparent. The concept was formally articulated by Frank Macfarlane Burnet in 1970, who proposed that lymphocytes could provide continuous surveillance against cells undergoing malignant transformation.

Our current understanding, however, reveals a much more dynamic relationship between cancer and immunity. This interaction is better described through the concept of cancer immunoediting, which comprises three interconnected phases.

1. Elimination: Immune Surveillance

During this initial phase, innate immunity, including NK cells, and adaptive immunity, particularly T lymphocytes, can work together to recognize and destroy emerging cancer cells.

This represents the classical manifestation of immune surveillance, in which immune mechanisms detect tumor-associated or tumor-specific molecular features and mount an effective response before a clinically apparent tumor becomes established.

Experimental studies have demonstrated that immune cells can play an important role in preventing the development of certain tumors.

NK cells are particularly important during this phase because they can rapidly recognize and destroy stressed or transformed cells. Interferon-gamma (IFN-γ) is also an important mediator of antitumor immunity and can contribute to tumor suppression through multiple signaling pathways.

2. Equilibrium

If some tumor cells survive the elimination phase, an equilibrium may be established.

At this stage, the immune system restrains tumor growth without necessarily eradicating every malignant cell. T lymphocytes and cytokines such as IL-12 and IFN-γ can contribute to maintaining some tumor cells in a state of prolonged dormancy or limited growth.

This phase may persist for years, creating a dynamic balance between tumor-cell evolution and immune control.

3. Escape

Eventually, some tumor-cell populations may acquire characteristics that enable them to evade immune detection and destruction. They can then proliferate more freely and eventually give rise to clinically detectable cancer. Tumors that escape immune control may have been shaped by immune pressure, favoring variants that are less immunogenic or more capable of resisting immune attack.

The concept of immunoediting therefore provides a profound example of co-evolution between cancer and the immune system within the same organism.

The immune system exerts continuous selective pressure, much as natural selection shapes populations over generations. Within this internal evolutionary landscape, highly immunogenic tumor cells may be preferentially eliminated, creating opportunities for less recognizable or more resistant variants to survive.

Thus, tumors that ultimately become clinically apparent may be understood, in part, as the survivors of this internal selection process.

They have acquired characteristics that make them more difficult for the immune system to recognize or eliminate.

Understanding this dynamic evolutionary interaction is fundamental to developing more effective and durable therapies. The objective is not simply to attack the tumor directly but also to overcome its remarkable capacity for adaptation and immune evasion.

This is one of the central challenges that modern immunotherapy seeks to address.

How Cancer Evades the Immune System: Despite continuous immune surveillance, cancer cells are remarkably adept at developing strategies that allow them to evade detection and destruction.

These mechanisms may be intrinsic to the tumor cell itself, involving alterations in its molecular composition or behavior, or extrinsic, arising from the environment that the tumor creates around itself: the tumor microenvironment.

Among the intrinsic mechanisms used by tumor cells to evade immune recognition are the following:

Loss or alteration of antigen expression. Tumor cells may stop expressing certain antigens that make them recognizable to the immune system. In this way, they can become less visible to tumor-specific T cells.

Reduced expression of MHC class I molecules. MHC class I molecules are essential for presenting intracellular peptides to CD8+ cytotoxic T lymphocytes. If tumor cells reduce or lose MHC class I expression, recognition by conventional CD8+ T cells can be impaired. Interestingly, however, reduced MHC class I expression may increase susceptibility to NK-cell recognition under certain circumstances, illustrating the complexity of immune surveillance.

High proliferative activity and genetic instability. Many tumors proliferate rapidly and exhibit genomic instability, allowing mutations and other alterations to accumulate. These changes can affect the expression of tumor antigens, antigen-presentation machinery, and signaling pathways involved in immune recognition. Tumor cells can therefore continuously alter their phenotype, making immune recognition and elimination more difficult.

Alteration of death-signaling pathways. Some tumors can interfere with apoptotic pathways or alter molecules involved in immune-cell killing. Certain cancers have also been reported to express Fas ligand (FasL), potentially contributing to immune evasion under particular circumstances.

Extrinsic mechanisms of immune evasion involve manipulation of the tumor microenvironment.

An immunosuppressive tumor microenvironment. Tumors can create an environment that actively suppresses effective immune responses. This may involve abnormal extracellular matrix, altered vasculature, hypoxia, suppressive metabolites, regulatory immune cells, and chronic inflammatory signaling.

Immunosuppressive cytokines. Tumor cells and surrounding stromal or immune cells can produce cytokines that inhibit effective antitumor immunity. Important examples include transforming growth factor beta (TGF-β) and interleukin-10 (IL-10), although their effects are highly context-dependent.

Angiogenesis and immune suppression. Tumors require new blood vessels to support their growth. Vascular endothelial growth factor (VEGF) is a key mediator of angiogenesis and can also interfere with dendritic-cell maturation and effective antigen presentation, thereby contributing to an immunosuppressive environment.

Immune Checkpoints: The Molecular Brakes: One of the most important mechanisms exploited by cancer cells involves immune checkpoints.

These are regulatory pathways that normally prevent immune responses from becoming excessive and damaging healthy tissues. They are expressed primarily on immune cells and interact with ligands expressed by other immune, stromal, or tumor cells.

Cancer can exploit these physiological mechanisms to suppress effective antitumor responses.

Two of the best-known examples are:

PD-1 and PD-L1. PD-1 is an inhibitory receptor expressed on activated T cells. Its ligand, PD-L1, may be expressed by tumor cells as well as by immune and other cells within the tumor microenvironment. When PD-L1 binds to PD-1, inhibitory signaling is transmitted to the T cell, reducing its activity. This can help the tumor evade immune destruction.

CTLA-4. CTLA-4 is another inhibitory receptor expressed by T cells. It limits T-cell activation during the early stages of the immune response, partly by competing with the stimulatory receptor CD28 for binding to CD80 and CD86 on antigen-presenting cells.

These mechanisms are essential for normal immune regulation. Cancer, however, can exploit them to protect itself from immune attack.

It is also important to distinguish acute inflammation from chronic inflammation. Acute inflammation is a vital protective response. By contrast, persistent inflammatory signaling within the tumor microenvironment can become tumor-promoting rather than effectively antitumor.

Chronic inflammation can contribute to tissue remodeling, angiogenesis, immune suppression, and cellular stress, creating conditions that favor tumor progression in certain cancers.

This raises the possibility that modulation of inflammatory and metabolic pathways could complement immunotherapy in selected settings. AMPK, for example, can influence inflammatory signaling and cellular metabolism, including pathways involving NF-κB, a family of transcription factors central to inflammatory and immune responses.

However, the relationship between AMPK, inflammation, metabolism, and cancer is highly context-dependent and remains an active area of research.

Immunotherapy and the New Oncology: Immunotherapy has transformed the treatment of cancer.

Whereas many conventional treatments act directly on tumor-cell survival or proliferation, immunotherapy seeks to mobilize, redirect, or enhance the patient’s immune response so that it can recognize and attack malignant cells.

Its principal strategies include:

• Enhancing immune recognition: helping immune cells recognize cancer cells more effectively.
• Removing inhibitory signals: blocking molecular pathways that restrain effective antitumor immunity.
• Increasing or redirecting cancer-reactive immune cells: expanding or genetically modifying immune cells so that they can recognize and attack specific tumor targets.

There are several major forms of cancer immunotherapy, each using a different strategy to mobilize the body’s defenses.

Immune Checkpoint Inhibitors: These drugs can act like a switch that releases the brakes on antitumor immunity.

As described above, tumors can exploit pathways such as PD-1/PD-L1 and CTLA-4 to inhibit T-cell activity. By blocking these inhibitory pathways, immune checkpoint inhibitors can restore or enhance T-cell responses in patients whose tumors are susceptible to this strategy.

Drugs such as ipilimumab, which blocks CTLA-4, and pembrolizumab and nivolumab, which block PD-1, have transformed the treatment of several cancers, including melanoma and various cancers of the lung, kidney, bladder, and head and neck, as well as Hodgkin lymphoma.

Other agents, including atezolizumab, avelumab, and durvalumab, target PD-L1.

Their fundamental achievement is not that they create a new immune response from nothing, but that they can restore or amplify an existing antitumor immune response by removing inhibitory constraints.

CAR-T Cell Therapy: CAR-T therapy is an advanced form of adoptive cellular therapy in which, in many currently established approaches, a patient’s own T lymphocytes are genetically modified so that they can recognize a defined antigen on cancer cells.

The process is highly specialized and individualized.

Collection of T cells. White blood cells, including T lymphocytes, are collected from the patient’s blood through a procedure known as leukapheresis. Blood passes through a specialized machine that separates the desired cells and returns the remaining blood components to the patient.

Genetic modification. In a specialized laboratory, a gene encoding a chimeric antigen receptor (CAR) is introduced into the T cells. This artificial receptor enables the modified cells to recognize a specific antigen on the surface of cancer cells. One important target is CD19, expressed by many B-cell leukemias and lymphomas.

Expansion. The genetically modified cells are cultured and expanded until a sufficient therapeutic dose is obtained. The manufacturing process can take several weeks.

Reinfusion. Once the CAR-T cells are ready, they are infused back into the patient, usually after preparative chemotherapy known as lymphodepletion. This treatment reduces competing lymphocyte populations and creates a more favorable immunological environment for the infused CAR-T cells to expand and function.

Once inside the body, CAR-T cells can recognize cancer cells carrying their target antigen. Upon recognition, they become activated, proliferate, and exert cytotoxic activity against the target cells.

Their persistence can provide prolonged antitumor activity, and in some patients this results in long-lasting remission.

CAR-T therapy has produced remarkable and sometimes durable responses in selected cancers of the blood and bone marrow, including certain leukemias, lymphomas, and multiple myeloma.

The field continues to evolve rapidly, with efforts to improve persistence, overcome antigen escape, reduce toxicity, and extend the approach to solid tumors.

Other Forms of Cancer Immunotherapy: The field of immunotherapy continues to expand and explore additional ways of mobilizing the immune system.

Targeted antibodies. These antibodies bind specific molecules on cancer cells or within the tumor microenvironment. Some block growth signals, while others recruit immune mechanisms to destroy the targeted cells. Antibody-drug conjugates (ADCs) combine antibody specificity with a cytotoxic payload, allowing the drug to be delivered preferentially to cells expressing the target. Bispecific T-cell engagers, or T-cell–redirecting bispecific antibodies, are designed to bind both a tumor-associated antigen and a molecule on T cells, bringing the two cell types into close proximity and facilitating tumor-cell killing.

Therapeutic cancer vaccines. Unlike preventive vaccines against infectious agents, therapeutic cancer vaccines are designed to stimulate an immune response against specific tumor antigens. Their objective is to strengthen the immune system’s ability to recognize and attack established cancer. Sipuleucel-T constitutes an example of a vaccine therapeutic authorized in certain contexts of prostate cancer, while many personalized and neoantigen-based vaccines remain under investigation.

Oncolytic virus therapy. This approach uses viruses, often genetically modified, that preferentially infect and destroy tumor cells. Tumor-cell destruction can also release tumor antigens and stimulate broader antitumor immune responses.

One example is talimogene laherparepvec (T-VEC), an oncolytic viral therapy used in selected patients with melanoma.

The field of immunotherapy, particularly advanced approaches such as CAR-T therapy, is also a major driving force behind personalized oncology.

Every tumor has a distinctive molecular landscape that can evolve over time and acquire new mechanisms of immune evasion.

This means that a “one-size-fits-all” approach is not always effective. Tumor biomarkers, antigen expression, immune-cell infiltration, mutational characteristics, and many other factors can influence the response to treatment.

The future of immunotherapy is therefore moving toward increasingly precise strategies in which comprehensive molecular analysis of both the tumor and the patient helps guide treatment selection.

The ultimate objective is to overcome the specific mechanisms of immune evasion present in each tumor and to maximize the probability of durable clinical benefit.

Table 2. Main Types of Cancer Immunotherapy

The Promise and the Limits of Immunotherapy: Immunotherapy has fundamentally reshaped the paradigm of cancer treatment, offering important advantages in selected clinical settings.

• Precision

The immune system possesses an inherent capacity for highly specific recognition.

Some forms of immunotherapy can therefore target malignant cells or tumor-associated molecular features with considerable specificity. This can reduce exposure of healthy tissues compared with some nonspecific cytotoxic approaches.

However, immunotherapy is not synonymous with complete precision or absence of toxicity. Because immune mechanisms themselves can damage healthy tissues, immune-mediated adverse effects remain an important limitation.

• Dynamism

The immune system is adaptable and capable of responding to changes within a tumor.

If a tumor evolves or acquires new characteristics, immune responses may potentially adapt as well. However, cancer can evolve more rapidly than the immune system can control it, and tumor heterogeneity can generate resistant populations.

• Immune Memory

One of the most intriguing properties of adaptive immunity is immune memory.

Once an effective immune response has been established against particular tumor antigens, memory cells may contribute to a faster response if those antigens are encountered again.

This provides a biological basis for the possibility of prolonged tumor control and may contribute to protection against recurrence in some circumstances.

But immune memory does not guarantee that a cancer will never return. Tumors can lose their target antigens, develop immune-evasion mechanisms, or persist in sites where immune control is less effective.

The Limitations of Immunotherapy: Despite its extraordinary potential, immunotherapy is not universally effective and presents important challenges.

Not every patient responds. Response rates vary widely according to cancer type, treatment, tumor biology, immune status, and many other factors. Tumor mutational burden, antigenicity, the presence of immune-cell infiltration, PD-L1 expression, defects in antigen presentation, and other molecular and cellular characteristics can influence therapeutic response.

Immune-related adverse effects. Activating or enhancing the immune system can sometimes cause immune-mediated toxicity. Immune cells may attack healthy tissues, producing inflammation or dysfunction in organs such as the skin, intestine, liver, lungs, endocrine glands, or kidneys. Other adverse effects can include fatigue, rash, gastrointestinal symptoms, musculoskeletal complaints, infusion-related reactions, and other treatment-specific toxicities.

Tumor resistance. Even when immunotherapy initially produces a strong response, tumors can develop resistance. They may lose or alter the targeted antigen, modify antigen-presentation pathways, change their microenvironment, or activate alternative immunosuppressive mechanisms.

The success of immunotherapy therefore lies in its ability to shift the balance of immune regulation toward effective tumor elimination.

Yet releasing the molecular brakes that normally restrain immune activity carries an inherent risk of injury to healthy tissues.

The immune-related adverse events associated with immunotherapy are a direct manifestation of this delicate biological balance.

By enhancing the immune system’s capacity to attack malignant cells, we may also increase the possibility that it will mistakenly attack healthy cells.

This underscores the critical need for continued research into biomarkers capable of predicting both therapeutic response and toxicity.

The goal is to develop increasingly precise strategies that maximize antitumor activity while minimizing immune-mediated adverse effects.

Understanding this balance is essential for optimizing treatment and safely expanding the reach of immunotherapy.

The Future: Combining Forces: The future of cancer treatment increasingly lies in combination strategies.

Immunotherapy may be combined with surgery, chemotherapy, radiotherapy, targeted therapies, or other forms of immunotherapy. In carefully selected settings, these combinations can enhance efficacy, overcome resistance, and improve clinical outcomes.

For example, lymphodepleting chemotherapy is routinely used before CAR-T-cell infusion. Its purpose is not to treat the tumor directly in this context but to reduce competing lymphocyte populations and create a more favorable environment for the infused cells to expand and function.

Beyond treating established disease, immunotherapy offers enormous potential for long-term disease control.

The capacity of the immune system to generate memory raises the possibility of reducing recurrence and, in the future, developing preventive tumor-directed vaccines for individuals at particularly high risk.

It is important, however, to distinguish these approaches from preventive vaccines already in use against infections that can cause cancer. Vaccination against human papillomavirus (HPV) and hepatitis B virus (HBV) already prevents a proportion of cancers by preventing the underlying infections. HPV and HBV vaccination prevent infections that can lead to cancer; they do not stimulate immunity against an existing tumor.

Preventive vaccines directed against tumor-specific antigens before cancer develops remain an active area of research.

Current research is also increasingly focused on understanding the biology of aging and immunosenescence, as well as how lifestyle, metabolic health, and potential geroprotective interventions may influence immune robustness throughout life.

Metabolism, Aging, and Cancer Immunity: There is a profound and complex interconnection between cellular metabolism, aging, and the effectiveness of immune surveillance against cancer.

Metabolism encompasses the processes through which cells obtain, transform, store, and use energy, as well as a vast network of biochemical reactions essential for cellular maintenance.

Metabolic dysregulation, including chronic hyperglycemia, can promote non-enzymatic protein glycation and the formation of advanced glycation end products (AGEs).

Protein glycation and the accumulation of AGEs can contribute to oxidative stress and inflammatory signaling. Persistent metabolic dysfunction can therefore influence the biological environment in which immune cells operate.

Conversely, activation of metabolic pathways such as AMPK promotes cellular adaptation to energy availability and influences multiple processes involved in cellular stress and inflammation.

AMPK can modulate inflammatory signaling, including pathways involving NF-κB, a family of transcription factors that plays a central role in immune and inflammatory responses.

The relationship is complex, however. AMPK signaling can have different consequences depending on the cell type, metabolic state, tumor type, and surrounding microenvironment.

These mechanisms remind us that the immune system does not function in isolation. Immune cells require energy, metabolic flexibility, appropriate nutrient availability, and intact cellular signaling to perform their functions effectively.

This suggests that interventions that support metabolic health and healthy aging, including a balanced diet, regular physical activity, adequate sleep, and avoidance of chronic metabolic dysfunction, may contribute to maintaining immune competence and reducing the biological conditions associated with cancer risk. A balanced diet, regular physical activity, adequate sleep, and the prevention of chronic metabolic disease support overall health and are associated with a lower risk of several chronic conditions, including some cancers. Their ability to enhance responses to specific immunotherapies, however, remains under investigation.

This holistic perspective recognizes that immune health is closely connected to metabolic health and to the biology of aging.

The organism is not a collection of independent systems. Its metabolism, immune function, cellular maintenance, and aging processes are intimately interconnected.

And perhaps this is one of the most important lessons that modern medicine is beginning to reveal.

The true victory over cancer is not having to fight the battle in the first place.

A New Way of Understanding Cancer: Immunotherapy has profoundly transformed the landscape of cancer treatment by harnessing one of the body’s most remarkable biological capacities: its ability to recognize and respond to abnormal cells.

By releasing inhibitory mechanisms, redirecting immune cells, or equipping them with new recognition capabilities, these innovative approaches have achieved durable remissions and prolonged disease control in many patients, including some with cancers that were once extremely difficult to treat.

Yet significant challenges remain.

Tumors evolve. They develop resistance. The immune system itself can become dysfunctional. And the same mechanisms that protect us can, when excessively activated, damage healthy tissues.

For this reason, the future of oncology will not depend on a single miraculous treatment. It will depend on a progressively deeper understanding of the complex relationship between tumor biology, immunity, metabolism, aging, and the individual characteristics of each patient.

Combination therapies, increasingly sophisticated cellular therapies, molecularly guided treatment, therapeutic vaccines, and strategies designed to remodel the tumor microenvironment are all moving oncology toward a more individualized future.

Our understanding of the immune system as an unceasing sentinel, now capable of being redirected and strengthened through scientific advances, offers a new horizon of hope in the fight against this complex disease.

But perhaps the most profound lesson lies beyond the treatment of cancer itself.

The human body possesses extraordinary mechanisms for maintaining its integrity. They operate continuously, silently, and largely beyond our awareness.

The challenge of modern medicine is increasingly not simply to replace these mechanisms when they fail, but to understand them, preserve them, and learn how to work with them.

The capacity of the human body to protect itself, once understood and intelligently harnessed, may become one of the keys to a healthier future.

Today’s research is tomorrow’s therapy