The genetic makeup of cancer cells is different from that of normal cells. Some of the genetic changes that occur include presence of one or more copies of chromosomes resulting to alteration in the normal chromosome number. Other genetic changes in cancer cells may even damage the chromosomes. Another very common genetic change in cancer cells is the division of the tumor cells where they divide moving towards the poles opposed to normal cells which divide in opposite directions.
This often results to fusion of three poles into a single daughter cell forming a daughter cell with extra chromosome(s). Continued division of such cells eventually results to production of chromosome sets that are completely different from the normal one. When the cancer cells accumulate during its development, many cells that are genetically different gets mixed up within the tumor and this results to a lower immune response of the patient to chemotherapy and other treatments as well.