USP8 and neoplasm: Furthermore, both the USP8 P618Q mutation identified in our patient and the hotspot S718P variants increased murine corticotroph tumor cell proliferation (USP8 P618Q vs. USP8 S718P fold change: 1.12 ± 0.03 vs. 1.14 ± 0.07, p < 0.05, Fig. 3B).