STAT1 and head and neck squamous cell carcinoma: Based on these data, we hypothesized that HNSCC cells can overcome loss of p53 and continue to upregulate APM with appropriate stimuli so long as they still express sufficient STAT1. We next knocked out STAT1 in one of the TP53-/- UM-SCC-74A clones to create multiple dual-knockout (DKO) clones.