The number of men and women in the United States alone that have cancer and are also old enough or young enough to have children is estimated at about 800,000 [source: American Society for Reproductive Medicine]. This puts both the doctor and patient in a difficult position. There's a strong desire to aggressively fight the disease and to do so promptly. But immediate action that doesn't take into account a patient's desire to eventually have children can be irreversible.
Advances in medicine have reduced the dangers posed by cancer treatments, but they still exist. The most prevalent threat to male infertility comes from radiation or chemotherapy. Both treatments can harm sperm [source: National Cancer Institute]. Naturally, the removal of one or both testicles or the prostate can reduce or eliminate the ability to reproduce.
Likewise, a hysterectomy or mastectomy directly impacts reproduction, while any treatment that influences the balance of a woman's hormones or harms her eggs can greatly reduce or erase her odds of having a successful pregnancy. Chemotherapy and radiation destroy cells that would otherwise continue to divide, regardless of whether those cells are healthy or not [sources: FertilityProRegistry; National Cancer Institute].
There are many options to preserve fertility -- some are common and others experimental -- but they have to be considered, and considered quickly, prior to undergoing cancer treatment. That's why the American Society of Clinical Oncology has created an outline of suggestions for doctors to follow while discussing the matter with patients [source: National Cancer Institute].