Cancer can be caused by genes a person inherits at birth or by outside influences that cause genetic mutations to occur in cells. According to Yale Medicine, inherited cancers that were present from the time of conception make up only a small percentage of the most common cancers, such as breast, colon and prostate cancer, and even less common cancers. In addition, even if inherited genetic mutations are present in the body, that does not mean the development of cancer is inevitable. According to Verywell Health, only around 5 to 10 percent of cancer cases can be attributed to inherited genetic mutations. More often than not, cancers that seem to “run in the family” are more likely a result of lifestyle or environmental factors that are shared by family members, such as eating the same unhealthy foods or a propensity to overindulge in alcoholic beverages