Which type of cell division occurs in cancer cells?

Cells reproduce by one of two distinct processes depending on cell type: mitosis, an equational division in which one parent cell yields two genetically identical daughter cells with the same (diploid) chromosome number, used for growth, repair, and replacement of ordinary somatic tissue; and meiosis, a reductional division confined to germ cells that halves the chromosome number to form gametes (egg and sperm).

Cancer cells are ordinary somatic (body) cells in which mutations in genes that regulate the cell cycle — such as proto-oncogenes and tumour-suppressor genes — disable the normal checkpoints on that cycle. The cells then keep undergoing mitosis without restraint, repeatedly producing genetically identical daughter cells and building up a tumour.

Checking the other options against this same reasoning:

• Meiosis occurs only in germ cells to form gametes, and never takes place in somatic tissue, so it cannot describe the division seen in a tumour.

• Mitosis together with meiosis would require meiosis to also run in body cells, which never happens outside the germline.

• No division at all contradicts the defining feature of cancer, which is excessive, uncontrolled division rather than an absence of it.

Since only mitosis operates in somatic tissue and drives this unchecked proliferation, mitosis is the type of cell division occurring in cancer cells.