Which statement best describes cancer cells? a. they grow as a single layer of cells. b. they cease to reproduce after 20–50 mitotic divisions. c. they reproduce only when needed to replace missing cells. d. they are not regulated by contact inhibition.

The statement that best describes cancer cells is option D. They are not regulated by contact inhibition. Contact inhibition is the inhibition or the stopping of the movement and division of cells from rapidly and uncontrollably dividing. Normally, cells should stop growing when they are in contact with each other, but the opposite happens in cancer cell growth.