Chemotherapy uses powerful cancer-killing medication to treat cancer. There are several different ways that chemotherapy can be used to treat lung cancer. For example, it can be: given before surgery to shrink a tumor, which can increase the chance of successful surgery (this is usually only done as part of a clinical trial)and Chemotherapy treatments are usually given in cycles. A cycle involves taking the chemotherapy medication for several days, then having a break for a few weeks to let your body recover from the effects of the treatment.