Cancer relapses are a serious concern. The possibility of relapse can often be estimated by the cancer type, extent and treatment at initial diagnosis. Talk to your oncologist
regarding the risks and possible treatments specific to your cancer.
The main reason for a cancer relapse is because an incomplete clearance of the cancer cells. Cancer cells are cells that grow without limitation, so even if one cell survives then it can multiply and cause the cancer to recur. There are two types of relapse--local and distant. A local relapse is if the cells appear in the same location (for example, breast cancer reappearing in the breast). A distant relapse is if the relapse is actually a metastases (for example, breast cancer appearing in the bone or lung). The completeness of the treatment and the cancer predict how likely a relapse is.
Different cancers require different interventions to prevent relapse. For example, in breast cancers the cells may grow because of estrogen--therefore some medicines to block estrogen will decrease risk (a common medicine is known as tamoxifen). Talk with your oncologist for more information on your case's specifics.
Another type of relapse is actually not a relapse--but a development of second type of cancer. Unfortunately some cancer treatment can actually cause other types of cancers. Talk to your oncologist if you could be at risk.
A key to any relapse is finding is early. Your oncologist may have you on a specific monitoring protocol (for example, repeat mammograms). I strongly encourage you to discuss this serious concern with your doctor