While wild-type PTPRD leads to downregulation of pSTAT3 (Y705) in HNSCC cells, overexpression of most HNSCC-derived mutants does not alter pSTAT3 (Y705) expression relative to vector control, suggesting that these mutations lead to loss of function, but not in a dominant negative manner. The gene discussed is PTPRD; the disease is head and neck squamous cell carcinoma.