Modern oncology kills cancer cells through a surprisingly diverse arsenal of strategies, from poisoning their DNA to starving them of nutrients to tricking them into self-destructing. The field has evolved well beyond the blunt-force approach of early chemotherapy, which worked largely by attacking any rapidly dividing cell. Today, treatments range from drugs that exploit a tumor’s own genetic weaknesses to engineered immune cells that hunt cancer with lethal precision. Understanding how each method actually destroys a cancer cell reveals why oncologists so often combine approaches and why resistance remains the central challenge of the field.
Chemotherapy and the Art of DNA Destruction
The oldest pharmaceutical strategy for killing cancer is also one of the most straightforward: damage the cell’s DNA so severely that it cannot survive. Cisplatin, one of the most widely prescribed chemotherapy agents for solid tumors, works by forming chemical crosslinks between strands of DNA, jamming the machinery that copies genetic material and triggering the cell’s built-in self-destruct program.1PubMed Central. Cellular responses to Cisplatin-induced DNA damage By interfering with DNA repair mechanisms, cisplatin essentially forces cancer cells into a corner where the damage is too extensive to fix, and apoptosis follows.2PubMed Central. Cisplatin in cancer therapy: molecular mechanisms of action
Not all chemotherapy drugs target DNA directly, though. Taxanes, a class that includes paclitaxel, take a different physical approach. Instead of damaging DNA, they stabilize structures called microtubules inside the cell. Microtubules normally assemble and disassemble as part of cell division; when a taxane locks them in place, the cell gets stuck mid-division. This “mitotic arrest” leads to catastrophic failure and, eventually, apoptosis.3PubMed Central. Cell death in cancer chemotherapy using taxanes Paclitaxel also promotes the expression of proteins that tip the cell toward self-destruction, so even cells that initially survive the mitotic block may still die afterward.4PubMed. Mechanisms of cancer cell death induction by paclitaxel: an updated review
What both approaches share is a dependence on apoptosis as the final executioner. Most conventional anticancer strategies used today, whether chemotherapy, radiation, or immunotherapy, ultimately funnel into the cell’s own programmed death pathways.5PubMed. Extrinsic versus intrinsic apoptosis pathways in anticancer chemotherapy In liver cancer cells, for example, chemotherapy drugs activate members of the p53 family of proteins, which then flip on death receptors and pro-death signals through both the cell’s internal pathway and its surface-receptor-driven pathway.6PubMed. Chemotherapy-induced apoptosis in hepatocellular carcinoma involves the p53 family and is mediated via the extrinsic and the intrinsic pathway This heavy reliance on apoptosis is also a weakness: cancers that disable their apoptotic machinery can survive treatment, which is one of the most common routes to drug resistance.
Radiation Breaks What Cells Cannot Fix
Radiation therapy kills cancer cells through a conceptually simple mechanism: it smashes their DNA. Ionizing radiation creates double-strand breaks, where both rails of the DNA ladder are severed at nearby points. These breaks are among the most dangerous forms of DNA damage because they are difficult for the cell to repair accurately.7PubMed Central. Targeting DNA Double-Strand Break Repair Pathways to Improve Radiotherapy Response Radiation also produces clusters of damage, where multiple types of lesions pile up in a small stretch of DNA. These clustered sites are especially hard to fix, and the severity of the damage depends partly on how much oxygen is present in the tissue.8PubMed. Biological consequences of radiation-induced DNA damage: relevance to radiotherapy
That oxygen dependence matters clinically. Tumors often contain regions starved of oxygen, and cells in those zones are measurably harder to kill with radiation. This is one reason radiation is frequently combined with drugs that sensitize tumors or with strategies that improve blood flow to the tumor before treatment.
Unleashing the Immune System
Your immune system already has cells built to kill cancerous cells. Natural killer cells, for instance, can detect transformed cells and destroy them either by injecting toxic granules containing perforin and granzymes or by triggering death receptors on the cancer cell’s surface.9PubMed. Mechanisms of natural killer cell-mediated cellular cytotoxicity The problem is that tumors are skilled at hiding. They put up molecular “don’t eat me” signals and suppress immune activity in their surrounding environment.
Immune checkpoint inhibitors are drugs designed to strip away those disguises. By blocking proteins like PD-1 and CTLA-4, which normally act as brakes on immune cells, checkpoint inhibitors reactivate exhausted T cells so they can recognize tumor-derived targets and kill cancer cells.10PubMed Central. The efficacy and safety of combination of PD-1 and CTLA-4 inhibitors: a meta-analysis The drugs do not kill cancer directly; they remove the barriers that prevent the immune system from doing its job.
CAR-T cell therapy goes a step further by engineering a patient’s own T cells to become targeted killers. These modified cells carry a synthetic receptor on their surface that locks onto a specific protein found on the tumor. Once engaged, CAR-T cells form a connection with the cancer cell and kill it through the same perforin-granzyme system that natural killer cells use, supplemented by death-receptor signaling and inflammatory cytokine release that can also damage the surrounding tumor tissue.11PubMed Central. Killing Mechanisms of Chimeric Antigen Receptor (CAR) T Cells The results in certain blood cancers have been dramatic, though solid tumors have proven far harder for CAR-T cells to penetrate.
Targeted Therapies and Oncogene Addiction
One of the most elegant strategies in modern oncology exploits a peculiar vulnerability of cancer cells. Despite carrying a staggering number of genetic mutations, many tumors become deeply dependent on a single overactive signaling pathway for their survival. This concept, known as oncogene addiction, means that blocking that one pathway can collapse the entire cancer cell, even though dozens of other mutations are still present.12PubMed. Oncogene addiction as a foundation of targeted cancer therapy: The paradigm of the MET receptor tyrosine kinase
Tyrosine kinase inhibitors exploit this dependency. In non-small cell lung cancers driven by activating mutations in the EGFR gene, treatment with drugs like gefitinib or erlotinib shuts down the downstream survival signals the cancer depends on, and the cells undergo apoptosis.13PubMed Central. Differential induction of apoptosis in HER2 and EGFR addicted cancers following PI3K inhibition The selectivity is remarkable compared to conventional chemotherapy: normal cells without the mutation are largely spared, which translates to fewer side effects. The catch is that cancers almost invariably develop secondary mutations that restore the survival pathway or reroute around the blocked signal, requiring an ongoing cat-and-mouse game with successive generations of targeted drugs.
Antibody-Drug Conjugates as Guided Missiles
Antibody-drug conjugates, or ADCs, marry the specificity of targeted therapy with the raw killing power of potent cytotoxic chemicals. An ADC consists of an antibody designed to bind a protein on the cancer cell’s surface, a chemical linker, and a toxic payload. When the antibody docks with its target, the whole package gets pulled inside the cell, where the linker is cleaved and the payload is released to kill the cell from within.14Clinical Cancer Research. A Novel HER3-Targeting Antibody–Drug Conjugate, U3-1402, Exhibits Potent Therapeutic Efficacy through the Delivery of Cytotoxic Payload by Efficient Internalization
The effectiveness of an ADC hinges on how well the cancer cell internalizes it. If something on the cell surface interferes with uptake, the payload never reaches its target. Research on mesothelin-targeting ADCs, for example, has shown that the presence of certain mucin proteins on the surface of ovarian cancer cells can reduce internalization and blunt cytotoxicity.15PLoS ONE. NAV-001, a high-efficacy antibody-drug conjugate targeting mesothelin with improved delivery of a potent payload by counteracting MUC16/CA125 inhibitory effects Getting the delivery right is therefore as important as selecting the right poison, and much of ADC development focuses on optimizing that internalization step.
Cell Death Beyond Apoptosis
Apoptosis gets the most attention, but it is not the only way a cancer cell can die. In fact, researchers have become increasingly interested in alternative death pathways precisely because they offer a way around apoptosis resistance. Ferroptosis, for instance, is an iron-dependent form of cell death mechanistically distinct from apoptosis. It works by overwhelming the cell’s ability to neutralize toxic lipid molecules, and triggering it has been shown to reverse drug resistance in cancers that have learned to dodge conventional cell death.16PubMed Central. Ferroptosis in cancer therapy: a novel approach to reversing drug resistance
Pyroptosis and necroptosis are two other non-apoptotic death pathways under active investigation. Unlike the quiet, tidy cleanup of apoptosis, these forms of death tend to be inflammatory: the dying cell bursts open, spilling its contents and alerting the immune system. When combined with immune checkpoint inhibitors, inducing pyroptosis, ferroptosis, or necroptosis has shown synergistically enhanced antitumor effects, even in tumors that had stopped responding to checkpoint drugs alone.17PubMed Central. Ferroptosis, necroptosis, and pyroptosis in anticancer immunity The inflammatory nature of these deaths appears to convert “cold” tumors, ones the immune system ignores, into “hot” tumors that draw immune attention.
Autophagy as a Double-Edged Sword
Autophagy is the cell’s housekeeping system for recycling damaged components. In most circumstances, it helps cells survive stress, which is generally bad news in cancer therapy because it can shield tumor cells from treatment-induced damage.18PubMed Central. Autophagy in Cell Survival and Death However, the relationship between autophagy and cancer cell fate is not a simple one. When autophagy is pushed to extremes in its extent or duration, it can flip from a survival mechanism to a death mechanism, a process sometimes called autosis.19PubMed. mTOR inhibitors in targeting autophagy and autophagy-associated signaling for cancer cell death and therapy
Drug-induced cancer cell death has been one of the settings where autophagy’s pro-death function most consistently appears.20PubMed Central. Autophagy in Cancer Cell Death This creates a therapeutic puzzle: should you block autophagy to prevent tumors from using it as a life raft, or should you hyper-stimulate it to push cells past the point of no return? The answer depends heavily on the tumor type, the treatment being used, and the genetic background of the cancer. Researchers are still working out when to hit the brakes and when to slam the accelerator.
Synthetic Lethality and the PARP Inhibitor Story
Synthetic lethality is a concept borrowed from genetics: two gene defects that are individually survivable become lethal when both occur in the same cell. PARP inhibitors are the first drugs designed around this principle to reach widespread clinical use. They work by blocking a DNA repair enzyme called PARP. Healthy cells can compensate using other repair pathways, but tumors carrying mutations in the BRCA1 or BRCA2 genes have already lost one of those backup pathways.21PubMed Central. The underlying mechanism for the PARP and BRCA synthetic lethality: clearing up the misunderstandings Knock out both repair routes, and DNA damage accumulates to a fatal degree in the cancer cell while normal cells, which still have functioning BRCA, survive.22PubMed Central. PARP inhibitors: Synthetic lethality in the clinic
The appeal of synthetic lethality extends well beyond BRCA-mutated cancers. Researchers are now screening for other gene pairs that might offer similar vulnerabilities, potentially opening this approach to a much broader range of tumors. The challenge is that identifying reliable synthetic lethal pairs in the messy genetic landscape of real tumors is far harder than demonstrating the concept in a lab dish.
Starving Cancer Cells
Cancer cells are metabolic gluttons. Their relentless proliferation demands a constant supply of nutrients, particularly glucose and certain amino acids. This dependency creates a potential weakness: if you cut off the supply, the cancer cell may not be able to adapt fast enough to survive.23PubMed Central. Attacking the supply wagons to starve cancer cells to death Amino acid depletion therapies, which interfere with the availability of specific amino acids the tumor depends on, have shown particular promise as a way to selectively kill cancer cells while largely sparing normal tissue.24PubMed. Amino Acid Depletion Therapies: Starving Cancer Cells to Death
The complication is that cancer cells are remarkably adaptable. In drug-resistant lung cancer cells, for example, researchers found that when glucose was restricted, the resistant cells ramped up their uptake of both glucose and an amino acid called glutamine, and shifted their energy production toward mitochondrial pathways. Blocking those adaptive metabolic responses restored the ability to kill the resistant cells.25PubMed. Targeting metabolic adaptive responses induced by glucose starvation inhibits cell proliferation and enhances cell death in osimertinib-resistant non-small cell lung cancer (NSCLC) cell lines The takeaway is that metabolic starvation alone may not be enough; you often need to anticipate and block the escape routes the cancer will take.
Light-Based Therapies
Photodynamic therapy and photothermal therapy use light to kill cancer cells, but through different physical mechanisms. Photodynamic therapy relies on a light-sensitive compound that, when activated by the right wavelength, generates reactive oxygen species that tear apart nearby molecules and kill cells. Photothermal therapy uses agents that convert light energy into heat, essentially cooking the tumor from the inside.26ACS Nano. Photodynamic and Photothermal Therapies: Synergy Opportunities for Nanomedicine
These two approaches complement each other in useful ways. Photodynamic therapy can reshape the tumor environment to make cells more sensitive to heat, while the increased blood flow from photothermal heating improves oxygen delivery, which in turn boosts the effectiveness of the oxygen-dependent photodynamic reaction.27PubMed Central. Combined Photodynamic and Photothermal Therapy and Immunotherapy for Cancer Treatment: A Review Both therapies are limited by how deeply light can penetrate tissue, which restricts them to superficial tumors or situations where fiber-optic catheters can deliver light directly to the target. They are also being explored in combination with immunotherapy, since the cell death they cause tends to be immunogenic, alerting the immune system to clean up surviving cancer cells.
Tumor Treating Fields and Mechanical Disruption
Among the more unusual approaches in clinical oncology, tumor treating fields (TTFields) use low-intensity alternating electric fields applied externally through adhesive arrays worn on the skin. These fields interfere with cancer cell division at two critical moments: during the formation of the mitotic spindle, when the cell is organizing its chromosomes, and during the final physical splitting of one cell into two.28PubMed Central. Tumor Treating Fields: At the Crossroads Between Physics and Biology for Cancer Treatment In biliary tract cancer cells, TTFields treatment produced visibly disorganized spindle structures and abnormal multipolar divisions, confirming that the fields physically disrupt the mechanics of cell division.29Scientific Reports. Tumor treating fields suppress tumor cell growth and induce immunogenic cell death biomarkers in biliary tract cancer cell lines
TTFields were originally shown to inhibit cancer cell growth through an anti-microtubule mechanism of action, and the approach was first demonstrated in animal tumor models and human brain tumors.30PubMed Central. Alternating electric fields arrest cell proliferation in animal tumor models and human brain tumors TTFields are currently approved for glioblastoma, one of the most treatment-resistant brain cancers, and trials are expanding into other tumor types. Because the fields primarily affect dividing cells, and healthy brain cells divide slowly if at all, the treatment has a relatively favorable side-effect profile compared to chemotherapy, though wearing the device continuously poses quality-of-life challenges.
Oncolytic Viruses Turn Cancer Against Itself
Oncolytic viruses are engineered or naturally occurring viruses that selectively infect and lyse cancer cells while sparing normal tissue. The killing itself is direct: the virus hijacks the cancer cell’s machinery to replicate, and eventually so many viral copies accumulate that the cell bursts open. But the real power of this approach lies in what happens after that lysis. When a cancer cell ruptures from viral replication, it releases tumor-associated antigens and danger signals that alert the immune system. This immunogenic cell death effectively unmasks the tumor, triggering dendritic cells and, subsequently, cytotoxic T cells to attack remaining cancer cells.31PubMed Central. Oncolytic viruses for cancer immunotherapy
In essence, the virus converts a tumor that was evading the immune system into one that provokes a strong immune response. This combination of direct destruction and immune activation is why oncolytic viruses are frequently being tested alongside checkpoint inhibitors, with the virus providing the initial spark and the checkpoint drug ensuring the immune response does not get suppressed again.
Why Cancer Cells Fight Back
No discussion of how cancer cells are killed is complete without addressing how they avoid being killed. Drug resistance is arguably the biggest obstacle in oncology, and it operates through multiple mechanisms simultaneously. One of the most well-characterized involves a family of pump proteins called ABC transporters. When overexpressed, these transporters actively eject chemotherapy drugs from the inside of the cancer cell, reducing the drug concentration to sub-lethal levels.32PubMed Central. Clinically-Relevant ABC Transporter for Anti-Cancer Drug Resistance In myeloma, the protein resistin has been shown to simultaneously boost anti-apoptotic defenses and increase the expression of these efflux pumps, creating a doubly protected cancer cell.33Blood. Resistin Induces Multidrug Resistance in Myeloma By Inhibiting Cell Death and Upregulating ABC Transporter Expression
The tumor’s physical environment contributes to resistance as well. Solid tumors tend to be more acidic than normal tissue, and this acidity creates a chemical barrier to many drugs. Weakly basic chemotherapy agents, which include a large number of common drugs, get trapped outside the cell in the acidic environment, never reaching their intracellular targets.34PubMed Central. Drug resistance and cellular adaptation to tumor acidic pH microenvironment Low oxygen levels within the tumor compound the problem by suppressing immune activity and reducing the effectiveness of radiation.35Journal of Drug Delivery Science and Technology. Targeting hypoxic and acidic tumor microenvironment by nanoparticles: A review These microenvironmental barriers explain why a drug that obliterates cancer cells in a lab dish can underperform dramatically in a living patient.
The Shift Toward Molecular Targeting
The history of cancer treatment is, in many ways, a story of increasing precision. The first wave of cytotoxic chemotherapy emerged after the Second World War, when researchers observed that nitrogen mustard compounds could shrink lymphomas. For decades, the field grew by discovering more chemical agents that could poison rapidly dividing cells, a blunt but sometimes effective strategy.36PubMed Central. Evolution of Cancer Pharmacological Treatments at the Turn of the Third Millennium The second major shift began in the 1980s, when advances in molecular biology made it possible to identify the specific proteins and pathways driving individual cancers, giving rise to targeted therapies.
Today, the frontier involves combining these approaches. A patient might receive a targeted kinase inhibitor to collapse the tumor’s primary survival pathway, a checkpoint inhibitor to unleash the immune system against surviving cells, and a metabolic intervention to cut off the cancer’s backup energy supply. The sheer number of ways researchers have learned to kill cancer cells has not yet translated into curing most advanced cancers, but it has transformed many previously fatal diagnoses into manageable chronic diseases. The field’s central frustration and its central hope are the same: cancer is not one disease with one solution, and neither is the effort to kill it.37PubMed. A history of cancer chemotherapy