Panobinostat enhances the antitumor activity of MK-1775 in a BxPC-3 xenograft model. A, body weights were measured every 3–4 days. B, tumor volumes were calculated according to the following formula: m12 × m2× 0.5236 (m1: short diameter; m2: long diameter). C–E, tumor specimens were fixed in 10% formalin, embedded in paraffin, and cut into 4 μM-thick slides for H&E (C) and PCNA staining (D). The proliferation index was calculated as proliferation index = PCNA positive cells/observed cells × 100% and graphed as means ± standard errors (E). F, apoptosis was measured using the TUNEL assay in the tumor specimens. G, apoptosis index was calculated as TUNEL-positive cells/observed cells × 100% and graphed as means ± standard errors. *** indicates p < 0.0005.