CDK4 and malignant peripheral nerve sheath tumor: However, among the tumors with normal CDK4 levels but low p16INK4a, there was some heterogeneity, as one tumor appeared to respond (MPNST-S14) but the other (Leiomiosarcoma-S29) showed similar levels of senescence markers to those in S14; however, the treatment response and the KI67 expression results were unclear.