KRT7 and neoplasm: Two of the pure SRCs showed positive expression of CK7, CK19 and MUC1, which indicated that the tumor cells had arisen from PB differentiation (cases 4 and 7); while one case was positive for CK19, MUC2 and MU5AC, which suggested that the pure SRC had arisen from the mixed type, consisting of I muscosa linig and PB epithelium (case 8).