FSCN1 and neoplasm: The main characteristics of ITPN are a solid nodular tumor macroscopically obstructing dilated ducts, no visible secreted mucin; tubulopapillary growth; uniform high-grade atypia throughout the neoplasm; easily recognizable necrotic foci; ductal differentiation as indicated by MUC1 and CK7 expression; absence of acinar differentiation as indicated by the absence of trypsin; absence of MUC2, MUC5AC, and fascine; and absence of KRAS and BRAF mutations [7].