POU1F1 and neoplasm: A small number of cells co-expressing NR5A1 and POU1F1 was observed in gonadotroph tumors (localized within the SF-1 gonadotroph cell cluster), as well as in two somatotroph tumor subtypes lacking NR5A1 expression (where these double-positive cells clustered within the PIT-1 cluster) (Fig. 4E).