BECN1 and neoplasm: Interestingly, S90 phosphorylation is essential for the Beclin 1 tumor-suppressing function, as shown in breast cancer MCF-7 xenografts [25], since a non-phosphorylatable mutant of Beclin 1 (Beclin 1 S90A) did not recapitulate the tumor suppression function of the wild-type Beclin 1.