E2F1 and thyroid cancer: The lack of bosutinib-induced apoptosis has also been observed in an in vivo model of thyroid cancer, in which mice treated with bosutinib exhibited a reduction in tumor growth, and this reduction was due to a decrease in key regulators of the cell cycle, including cyclins, CDK4/6, and E2F1, and not due to an increase in apoptosis [17].