RB1CC1 is implicated in the regulation of RB1 expression. It functions as a DNA-binding transcription factor. RB1CC1 is a potent regulator of the RB1 pathway and a mediator that plays a crucial role in muscular differentiation. The expression of RB1CC1 is, thus, a prerequisite for myogenic differentiation. RB1CC1 is frequently mutated in breast cancer and shows characteristics of a classical tumor suppressor gene.