And each cancer has its own genetic identity, or fingerprint, created by the DNA in its cells. So two people with breast cancer who are the same age, height, weight, and ethnicity, and who have similar medical histories, almost surely have two very different cancers.The only thing the cancers have in common is that they started from a breast tissue cell.o even though every cell of a cancer is related to the same original parent cell, all the cells that make up a cancer are not the same. The idea that different kinds of cells make up one cancer is called tumor heterogeneity..