Multiple Primary Tumors Over a Lifetime.

The frequency of patients living after a cancer diagnosis continues to increase due to the rising incidence of cancer as well as the improved survival of cancer patients thanks to advances in cancer research and treatment. The risk of multiple primary cancers is also increasing due to increasing numbers of cancer survivors, long-term side effects of chemotherapy and/or radiation therapy, increased diagnostic sensitivity, and persisting effects of genetic and behavioral risk factors. Multiple primary cancers are defined as more than one synchronous or metachronous cancer in the same individual. Although several different definitions of multiple primaries have been proposed, the main definitions come from the Surveillance, Epidemiology, and End Results (SEER) Program and the International Association of Cancer Registries and International Agency for Research on Cancer (IACR/IARC). Depending on the definition, overall reported frequency of multiple primary cancers varies between 2.4% and 17%. Underlying causes for multiple primary cancers may include host and lifestyle-related factors, environmental and genetic factors and treatment related factors. Significant temporal changes have been found in the prevalence of cancer risk factors (ie, smoking, alcohol consumption, obesity) as well as advances in diagnostic sensitivity and improved screening programs that may affect the incidence of second or more cancers. In this review, the literature on multiple primary cancers is analyzed with a focus on clinical situations where a treating physician should take into consideration the possibility of multiple primaries.