The incidences of cancer started shooting up in the year 1991. Since a decade the cancer cases increased by a factor of three. There is simply no complete cure to this dreadful condition. It involves changes in the genome leading to uncontrolled cellular proliferation, transformation, invasion, metastasis, apoptosis suppression, and angiogenesis. The environmental factors such as chemicals, radiations, viruses, microbes, and hormones cause cancer. Apart from the above reasons, there are more factors involved. The cell follows a cyclical pattern of division involving different phases. It includes the G1, S, G2, and the M phases respectively. The transition of one phase from the other involves checkpoints. The CDK/cyclin complexes mainly control the cell cycle. The checkpoints determine the damaged DNA. They also help in checking the problems in the cell cycle machinery. Hence, they play a crucial role in permitting normal cells to continue. Problems in the cell cycle checkpoints trigger cancerous conditions. Certain viruses such as retroviruses cause cancer. They increase the oncogenic products. Also, for the normal cells, apoptosis plays a crucial role. The cancer cells do not undergo apoptosis.