Cancer is not one illness but a family of hundreds of diseases, so there can’t be a single cure for all of them.1Comprehensive Cancer Centers. Comprehensive Examines Why People Believe Only One Cancer Exists The deeper problem is that one tumour isn’t a uniform mass. It is a changing population of cells, and treatment tends to select the few that survive. Still, “incurable” isn’t the whole picture: some cancers are routinely cured, and others can now be held in check for decades.
Why Every Cancer Is Different
Estimates range from more than 100 to over 200 kinds of cancer, all sharing uncontrolled cell growth.2Cancer Research Institute. Exploring the Different Types of Cancer and Treatment Options Almost every tissue in the body can give rise to cancer, and some tissues produce several types.3Scientific American. How Cancer Arises A drug designed for one type, such as a breast cancer drug, often does little against another.
Even within a single type, the differences run deep. Two tumours from the same organ and cell type can look identical under a microscope and still be driven by very different genetic changes.4Comprehensive Cancer Centers. Comprehensive Examines Why People Believe Only One Cancer Exists So doctors increasingly test a tumour’s genes to choose treatment, not just its location. Drug trials are also being designed around a tumour’s genetic markers rather than averaging results across everyone with the same organ affected.5PubMed Central. New clinical trial design in precision medicine: discovery, development and direction
A cancer’s name usually comes from the tissue where it started and the cell type involved, which is why “lung cancer” covers several quite different diseases. Two people told they have the same named cancer can therefore be given different treatments, which is not a sign that someone is getting worse care.
This also makes “when will cancer be cured?” a misleading question. Progress comes cancer type by cancer type, not as one breakthrough.
A Tumour Is a Crowd of Changing Cells
Most tumours carry hundreds to hundreds of thousands of genetic changes, a sign they mutate faster than normal cells.6PubMed Central. Evolution of the cancer genome Both outside damage and everyday stress inside the cell can overwhelm the normal DNA repair systems.7PubMed Central. Endogenous DNA Damage as a Source of Genomic Instability in Cancer The tumour then keeps generating new variants as it grows, and abilities like resisting treatment, coming back and spreading depend on this ongoing variety.8PubMed Central. Evolution of the cancer genome
Each time a cell divides, its DNA is copied, and in tumour cells with weakened repair, more copying errors survive. Most errors do nothing or harm the cell, but occasionally one gives a cell an advantage such as faster growth. That cell’s descendants form a branch in the tumour, and the process repeats, creating a family tree of related but different cell groups.
The result is that most cancers contain genetically different groups of cells side by side, not identical copies.9PubMed. Genetic heterogeneity and cancer drug resistance A treatment that kills most cells can miss a small group that was already resistant.10PubMed. Genetic heterogeneity and cancer drug resistance Under treatment, that rare group expands and becomes the new tumour.11PubMed. Genetic heterogeneity and cancer drug resistance Shrinkage on a scan doesn’t mean every cell type is gone, so doctors often combine drugs that attack in different ways.
How Cancer Cells Survive the Drugs
Many cancer cells use protein pumps in their outer wall to push chemotherapy drugs back out.12PubMed. ABC transporters in cancer: more than just drug efflux pumps The pumps move drugs out before they can reach their target inside. In lab-grown cancer cells, the same pumps made cells resist even newer drug types, and blocking the pump restored the drug’s effect.13PubMed Central. The drug efflux pump MDR1 promotes intrinsic and acquired resistance to PROTACs in cancer cells
Cells with more pumps survive a dose that kills their neighbours, so those cells come to dominate. And because one pump can move out several unrelated drugs, a tumour resistant to one chemotherapy drug may also tolerate others.
Cancer cells can also switch into a different state that no longer relies on the pathway blocked by a targeted drug, one aimed at a specific fault in the cancer cell.14PubMed. The great escape: tumour cell plasticity in resistance to targeted therapy The switched cells grow slowly and can either become sensitive again when treatment stops or become permanently resistant.15PubMed. The great escape: tumour cell plasticity in resistance to targeted therapy This switching has been seen in prostate cancer, lung cancer and melanoma.16PubMed. The great escape: tumour cell plasticity in resistance to targeted therapy It works by changing which genes are turned on, not by changing the genes themselves.17PubMed. Cancer cell plasticity, stem cell factors, and therapy resistance: how are they linked?
That makes a state switch different from a mutation. A mutation is a permanent change in the DNA, while a switch is a cell changing its behaviour while keeping its DNA. Because it can reverse, some patients respond again after a treatment break, and doctors sometimes use this when retrying a drug later.
Tumours also constantly rewire how they get energy as their surroundings change.18PubMed Central. Targeting metabolic plasticity and flexibility dynamics for cancer therapy A tumour may contain groups of cells with different fuel habits, and treatment selects the hardiest.19PubMed Central. Metabolic Adaptations in Cancer Progression: Optimization Strategies and Therapeutic Targets
Hiding From the Immune System and Drugs
Cancer cells reduce the markers on their surface that let immune “killer” cells recognise them.20PubMed Central. Immune evasion in cancer: mechanisms and cutting-edge therapeutic approaches Tumours also raise brake signals such as PD-L1 that switch off attacking immune cells.21PubMed Central. Immune evasion in cancer: mechanisms and cutting-edge therapeutic approaches Immune cells near a tumour can then become exhausted and stop fighting.22Global Journal of Cancer Therapy. Mechanistic basis for Cancer Immune Evasion and role of immune checkpoint blockades in Immuno-Oncology
Exhaustion is a shutdown, not death of the cell. Simply having immune cells inside or near a tumour therefore doesn’t mean the tumour is being controlled.
Immunotherapy drugs called checkpoint inhibitors release those brakes and can help some patients, but tumours that hide their markers may still escape. The drugs only help if immune cells can see the tumour, so tumours rich in visible markers tend to respond better. Doctors may test for PD-L1 before choosing these drugs, though the result is only one guide and does not reliably predict who will benefit.
Many tumours also build up dense, stiff tissue around clusters of cancer cells that keeps drugs out.23PubMed Central. Extracellular Matrix in the Tumor Microenvironment and Its Impact on Cancer Therapy This tissue squeezes the tiny blood vessels that would carry drugs into the tumour’s core.24PubMed Central. Extracellular matrix and its therapeutic potential for cancer treatment The same barrier blocks newer tiny drug-carrying particles.25PubMed Central. Tumor extracellular matrix modulating strategies for enhanced antitumor therapy of nanomedicines There is a hopeful sign, though: in colorectal cancer spread to the liver, breaking down part of this tissue improved chemotherapy.26PubMed Central. Extracellular matrix and its therapeutic potential for cancer treatment
Why Cancer Can Return Years Later
Cancer cells can leave the original tumour early and settle quietly in distant organs.27PubMed. The dormant cancer cell life cycle A tumour can shed cells into the bloodstream or lymph vessels while it is still small, well before it is found. Most of these cells die, but a few can lodge in organs such as bone or liver and settle in.
They can then stay dormant and later reactivate, causing a relapse after the first tumour was successfully treated.28World Journal of Oncology. Tumor Dormancy: Biologic and Therapeutic Implications In breast cancer, such dormant cells can produce metastasis, meaning spread to other organs, up to two decades after diagnosis.29PubMed Central. Breast Cancer Stem Cells as Drivers of Tumor Chemoresistance, Dormancy and Relapse: New Challenges and Therapeutic Opportunities Slow-growing or resting cells escape chemotherapy, which mainly kills dividing cells.30PubMed Central. Breast Cancer Stem Cells as Drivers of Tumor Chemoresistance, Dormancy and Relapse: New Challenges and Therapeutic Opportunities Scans cannot see a handful of cells, so surgery that removes the whole visible tumour can still leave some behind.
Finding them is hard too. Blood tests that look for tumour DNA can miss very small amounts left behind.31PubMed Central. Liquid Biopsy to Detect Minimal Residual Disease: Methodology and Impact New cell groups the test wasn’t designed to catch can also emerge.32PubMed Central. Liquid Biopsy to Detect Minimal Residual Disease: Methodology and Impact
That is why remission is not the same as cure. Doctors often speak of cure only after years without return, and the risk of return usually falls over time but varies by cancer type.
Follow-up appointments continue for years for the same reason. They aim to catch a return early, when it may be easier to treat. Schedules usually become less frequent over time, and reporting new symptoms promptly matters.
Why Doctors Can’t Just Use Stronger Doses
Most chemotherapy drugs have a very narrow gap between a helpful dose and a harmful one.33PubMed. Therapeutic drug monitoring of cancer chemotherapy Fast-dividing healthy cells like hair and gut lining are hit too, and side effects set a hard ceiling on how much drug can be given.
In practice, the dose that kills enough cancer cells can be close to the dose that harms bone marrow, gut lining or nerves. Doctors therefore watch blood counts and symptoms during treatment and may delay a cycle to let the body recover. Delays and dose reductions are usually a safety measure, not a sign that the treatment is failing.
The same dose can also reach very different levels in different people’s blood.34PubMed. Therapeutic drug monitoring of cancer chemotherapy So some centres measure drug levels in the blood to fine-tune dosing.35PubMed. Therapeutic drug monitoring of cancer chemotherapy For some targeted drugs, research suggests doses up to 10 times lower than the approved dose may work, sparing side effects.36PubMed Central. Optimizing the Therapeutic Window of Targeted Drugs in Oncology: Potency‐Guided First‐in‐Human Studies
It is reasonable to ask the care team whether dose adjustments are possible if side effects are severe, and whether blood level testing applies to your drug. A dose should never be changed without them.
Cancers That Can Be Cured or Controlled
Testicular cancer is usually cured with chemotherapy. Its root cells are more sensitive to chemotherapy than other cells in the tumour, unlike most cancers.37Cornell University College of Veterinary Medicine. Study reveals why testicular cancer responds to chemo Several chemotherapy-curable cancers come from cells naturally primed to self-destruct when damaged.38PubMed Central. Chemotherapy curable malignancies and cancer stem cells: a biological review and hypothesis
Testicular cancer cells come from germ cells, which are prone to self-destruct when their DNA is damaged. Chemotherapy damages DNA, so these cells tend to die rather than repair themselves. Even when the cancer has spread, many patients can still be cured, which is unusual among advanced cancers.
Control is a different kind of success. Daily pills that block the faulty protein in chronic myeloid leukaemia have transformed the disease over two decades.39PubMed Central. Tyrosine kinase inhibitors in the treatment of chronic phase CML: strategies for frontline decision-making The disease is driven by one abnormal protein that tells blood cells to keep multiplying, and the pills remove that growth signal. Because nearly all the cancer depends on this single fault, one drug can control the disease in most patients.
People on these pills live nearly as long as the general population, and as long if their response is deep.40PubMed Central. Prospective Analysis: Relative Survival in Patients with Chronic Myeloid Leukemia in Chronic Phase in the Era of Tyrosine Kinase Inhibitors Some people with long, deep responses can stop the pills under close medical monitoring.41PubMed Central. Tyrosine kinase inhibitors in the treatment of chronic phase CML: strategies for frontline decision-making
For many cancers the goal is becoming control, much like diabetes. Long survival with treatment is a real, meaningful outcome, and it is worth asking your doctor whether the aim is cure or control.
New Strategies That Work With Evolution
Adaptive therapy uses less than the maximum dose, leaving drug-sensitive cells alive on purpose.42PubMed. Adaptive Therapy and the Cost of Drug-Resistant Mutants Those sensitive cells compete with resistant ones and hold them back.43PubMed Central. A survey of open questions in adaptive therapy: Bridging mathematics and clinical translation The aim is to control the tumour for longer rather than eliminate it.44bioRxiv. Modifying adaptive therapy to enhance competitive suppression
Adaptive therapy starts at a standard dose while the doctor tracks the tumour with scans or blood markers. When the tumour shrinks to a set level, the drug is paused so sensitive cells can regrow. When it grows back to a set level, the drug restarts, and the cycle repeats. It is still mostly in trials, not standard care.