Chemotherapy is a drug-based treatment used primarily to destroy cancer cells, but it also plays a role in treating certain autoimmune diseases and preparing the body for bone marrow transplants. The drugs work by targeting cells during growth and division, disrupting the cycle that allows them to copy their genetic material and multiply. Because cancer cells divide faster than most normal cells, they’re especially vulnerable to this disruption.
How Chemotherapy Targets Cancer Cells
Every cell in your body goes through a predictable cycle when it reproduces: it grows in size, copies its DNA, and splits into two new cells. Chemotherapy drugs interrupt one or more stages of this process. Some damage the DNA directly so the cell can’t make copies of itself. Others mimic the nutrients a cell needs to grow, essentially tricking it into starving. Still others block the cell’s ability to physically divide in two.
Different classes of drugs attack different phases of the cycle, which is why oncologists often combine multiple drugs in a single treatment plan. A combination can hit cancer cells at several vulnerable points, making it harder for them to survive or develop resistance.
The Four Goals of Cancer Treatment
Not every round of chemotherapy has the same purpose. The goal depends on the type of cancer, how far it has spread, and where you are in your overall treatment plan.
- Curative treatment aims to eliminate cancer entirely. This is most common with cancers that respond strongly to chemotherapy, such as certain leukemias, lymphomas, and testicular cancers.
- Neoadjuvant treatment is given before surgery. It shrinks tumors so they’re easier to remove. In some cases, it eliminates the tumor completely, making surgery unnecessary.
- Adjuvant treatment is the opposite: it comes after surgery. The goal is to destroy any remaining cancer cells that imaging can’t detect, reducing the chance of recurrence.
- Palliative treatment is used when a cure isn’t the primary objective. Here, chemotherapy slows cancer growth, shrinks tumors that cause pain or pressure, and helps manage symptoms to improve quality of life.
Many people receive chemotherapy in more than one of these roles over the course of their care. Someone might get neoadjuvant chemo to shrink a breast tumor, have surgery, and then receive adjuvant chemo afterward.
Cancer Types Commonly Treated With Chemotherapy
Chemotherapy remains a core treatment for a wide range of cancers. It’s especially central in blood cancers like leukemia and lymphoma, where there’s no solid tumor to remove surgically. It’s also a standard part of treatment for breast cancer, lung cancer, colorectal cancer, ovarian cancer, and bladder cancer, though the specific drugs and combinations vary significantly between them.
For some cancers, chemotherapy is the main treatment. For others, it works alongside surgery, radiation, immunotherapy, or targeted therapy. The trend in oncology has been toward combining chemotherapy with newer treatments rather than replacing it outright. Your cancer type, stage, and genetic profile all factor into whether chemotherapy is part of the plan.
Preparing for Bone Marrow Transplants
One of chemotherapy’s most important non-standard roles is conditioning the body before a stem cell or bone marrow transplant. This preparation phase, which typically takes one to nine days, uses high-dose chemotherapy (sometimes combined with radiation) to accomplish three things at once: destroy any remaining cancer cells, suppress the immune system so it won’t reject the incoming donor cells, and clear space in the bone marrow for new stem cells to take hold.
The conditioning doses are significantly higher than standard chemotherapy, and the side effects are more intense. Full recovery can take months. The specific regimen depends on the type of cancer being treated, the type of transplant, and what treatments the person has already received.
Uses Beyond Cancer
Several chemotherapy drugs are used at lower doses to treat autoimmune conditions, where the immune system mistakenly attacks healthy tissue. The same ability to suppress rapidly dividing immune cells that makes these drugs effective against cancer also helps calm an overactive immune response.
Methotrexate, originally developed as a cancer drug, is now one of the most widely prescribed medications for rheumatoid arthritis. Cyclophosphamide is used in severe cases of lupus, particularly when the kidneys are affected, and has been studied in over 200 patients with aplastic anemia and other autoimmune diseases. Rituximab, which depletes a specific type of immune cell, treats autoimmune blood disorders including conditions where the body destroys its own red blood cells or platelets. When these drugs are used for autoimmune diseases, the doses are generally much lower than in cancer treatment, and the side effect profile is milder.
How Chemotherapy Is Delivered
Intravenous infusion, where the drug flows directly into a vein, is the most common delivery method. It gets medication into the bloodstream efficiently and allows precise control over dosing. Most people receiving IV chemo have a central venous catheter placed to avoid repeated needle sticks over weeks or months of treatment.
Oral chemotherapy, taken as pills or liquid, is more convenient and can be done at home. Some treatment plans combine both IV and oral drugs at the same time. Less common routes include injections into muscle or under the skin, and intrathecal delivery, where the drug is injected into the fluid surrounding the spinal cord to treat cancers that have reached the central nervous system.
When cancer is confined to a specific area, regional chemotherapy can deliver drugs directly where they’re needed. This includes pumping medication into a single artery feeding a tumor, or placing heated chemotherapy solution directly into the abdominal cavity during surgery for cancers like ovarian or colorectal cancer that have spread within the belly.
What a Treatment Cycle Looks Like
Chemotherapy is given in cycles: a period of treatment followed by a rest period. The treatment days might involve a single session or several days of infusions, depending on the drugs used. Rest periods, which commonly last one to three weeks, give your body time to recover and rebuild healthy cells that were affected alongside the cancer cells.
A full course of chemotherapy might involve four to eight cycles, spanning three to six months, though this varies widely. Some people receive maintenance chemotherapy at lower doses for a year or longer to keep cancer from returning. Your oncologist adjusts the schedule based on how your cancer responds and how your body tolerates the drugs, so two people with the same diagnosis might follow different timelines.
How Different Drug Classes Work
There are four major categories of chemotherapy drugs, each with a distinct strategy for killing cancer cells.
Alkylating agents were among the first cancer drugs developed and remain the most widely used class. They work by directly damaging a cell’s DNA so it can’t reproduce. Platinum-based drugs work similarly but through a slightly different chemical mechanism. Both classes are used across many cancer types but tend to be most effective against slower-growing cancers.
Antimetabolites take a subtler approach. They mimic the building blocks a cell needs to copy its DNA, tricking the cell into incorporating them. Once inside, they block the copying process, effectively starving the cell of what it needs to divide.
Plant alkaloids prevent cell division at the final physical step, blocking a cancer cell’s ability to split into two daughter cells. Antitumor antibiotics (unrelated to the antibiotics used for infections) bind to DNA and prevent the cell from reading its own genetic instructions to make the proteins it needs to survive. They cause the DNA strands to uncoil, which stops reproduction entirely.
Most treatment plans combine drugs from two or more of these classes, attacking cancer through multiple mechanisms simultaneously. This combination approach is one of the reasons chemotherapy has become more effective over the past several decades.