Rb1, or retinoblastoma protein, is a crucial tumor suppressor in the human body. It plays a significant role in regulating the cell cycle, particularly by controlling the transition from the G1 phase to the S phase. When functioning properly, Rb1 helps prevent excessive cell growth and division, which can lead to cancer. Mutations in the Rb1 gene are associated with various cancers, most notably retinoblastoma, a rare eye cancer that primarily affects young children. The loss of Rb1 function can lead to uncontrolled cell proliferation, contributing to tumor formation. Understanding Rb1 is essential for cancer research and developing targeted therapies.