CDKN1A and neoplasm: The repression of class I and class II MHC complex components may be an evolutionarily conserved function of PRC2 in modulating tumor microenvironment, and the suppression of p21/CDKN1A has been explicitly shown to be required for tumorigenesis in lymphoma.[16, 38] Interestingly, p21/CDKN1A is also a well‐known downstream effector of BMP signaling and pSMAD1/5 directly binds its promoter.