BECN1 and neoplasm: The notion that Beclin 1 can function as a tumor suppressor protein is supported by several well-known studies, including the observations that endogenous Beclin 1 protein expression is frequently low in human breast epithelial carcinoma cell lines and tissue, but is expressed ubiquitously at high levels in normal breast epithelia; BECN1 is monoallelically lost in 40 to 75% of human breast, and ovarian cancers6.