Classes of cancer drugs and how they work

In oncology, surgery is one of major considerations in treatment of cancer. In some stages of cancer, we subject patients to surgery with chemotherapy or surgery with radiation. Surgery alone can be used as treatment for cure once the resection of the tumor margins is complete.The two major kinds of treatment in cancer with surgery are the adjuvant and neo-adjuvant chemotherapy.The adjuvant chemotherapy is always given after surgery to remove the cancer. This is because there may still be some cancer cells left behind after surgery. When drugs are used to kill those unseen cancer cells the treatment is known as adjuvant chemotherapy. Adjuvant treatment can also be given after radiation. An example of this would be adjuvant hormone therapy after radiation for prostate cancer.Chemotherapy can be given before the main cancer treatment such as surgery or radiation. Giving chemotherapy first can shrink large tumors that make it easy to remove by surgery. If a big cancerous tumor shrinks, it decreases in size and this facilitates radiation treatment. This kind of treatment is known as neo-adjuvant treatment.Neo-adjuvant chemotherapy can also kill small deposits of cancer cells that cannot be seen on imaging exams such as CT-scans and x-rays.Cancer drugs or chemotherapy drugs are divided into various classes based on their mechanism of action, chemical structure as well as their capacity to interact.It is important to know how a drug works in order to predict its side effects. This helps oncologists to decide which drugs are likely to work well in combination or not. Adequate information on chemotherapy properties is crucial as it helps oncologists plan or know when each of the chemotherapy regimen should be given.One of the most commonly used classes of chemotherapy drugs is the alkylating class. Examples of the alkylating class that are commonly used are the platinum drugs such as cisplatin, oxalaplatin and carboplatin.The alkylating agents work as they directly damage DNA of the cancer cell and this prevents cancer from reproducing. The cancer cells have cycles of development or division as it has been seen in normal cells. Drugs found in the alkylating class work in all phases of cell cycle and are not phase specific.These drugs are used to treat cancers such as leukemia, lymphoma, Hodgkin disease, multiple myeloma, and sarcoma, as well as cancers of the lung, breast, and ovary. However, because of their potential to damage DNA, they can sometimes damage bone marrow and in rare cases cause acute leukemia. The risk of leukemia from alkylating agents is always dose-dependent. This means that the risk is small with lower doses, but goes up as the quantity of drug circulation in the body increases. People at risk to develop leukemia are those exposed to the drug between 6 to 10 years.Another class of drugs is known as the anti-metabolite chemotherapy drugs or regimens. They work by interference of DNA and RNA growth of the cancer cell. They are commonly used to treat leukemia’s, cancers of the breast, ovary, and the gastro-intestinal tract system. But can also work on other types of cancers. Examples of such drugs include 5-fluorouracil (5-FU), Gemcitabine among many others.The topoisomerase inhibitors interfere with the enzyme topoisomerase that help separate the strands of cancerous DNA. This class of drugs is used to treat some types of leukemia, lung, ovarian, and gastrointestinal cancers as well as in other cancers. Examples of such drugs include irinotecan (CPT-11) and etoposide (VP-16). Mitotic inhibitors are a class of drugs natural products or plants. They inhibit enzymes from making proteins needed for cell reproduction or stop mitosis. They are used in treatment of various types of cancers such as the breast, lung, myelomas, lymphomas, and leukemia’s. Other classes not discussed here include hormonotherapy, immunotherapy and anti-tumor antibiotics, commonly used medications in treatment of cancer as well. Dr Joseph Kamugisha is a resident oncologist in Jerusalem, Israel