Taken very broadly, chemotherapy is any treatment that you take into your body with the intent of stopping dividing cells. This can refer to practically anything in cancer medicine. But in many cases what we’re referring to specifically is “cytotoxic chemotherapy,” compounds that directly disrupt cell division. This includes classes of agents such as taxanes (bind microtubules and prevent cell division), anthracyclines (DNA-damaging antibiotics), platinum agents (bind DNA and cause breaks), and nitrogen mustards.
The key distinguishing feature of cytotoxic chemotherapy is that it has no specificity. Chemotherapy impacts any rapidly dividing tissue. This is generally bad news for your gut (hence the diarrhea), your hair follicles, and especially your one marrow (hence the low platelets, anemia, and increased risk of infection). But in many types of cancer, chemotherapy can be an effective tool for getting the disease under control. In a few cases, chemotherapy can even lead to a cure in a high percentage of patients.