Breast cancer begins when a normal breast cell undergoes a mutation process of the genes that control cell growth. Breast cancer cells, like all cells, grow by cellular division. Since each cell division takes 1- 2 months, the process to detect a tumor growing in the body can be between 2 to 5 years. Since tumor cells multiply and divide exponentially—one cell becomes two, two cells become four, and so on—a tumor will increase more rapidly in size the larger it is. According to the Robert W. Franz Cancer Research Center at Providence Portland Medical Center, breast cancer cells need to divide at least 30 times before they are detectable by physical exam. Tumors that are triple negative have greater increases in volume and shorter doubling times than those that are estrogen positive and Her 2 negative. The question of how long a breast cancer has been present in the body when it is diagnosed can be difficult to determine, but it’s likely that many tumors began a minimum of five years before they were detected.