MKI67 and small cell lung carcinoma: Because the Ki-67 index was not substantially different according to the TROP2 expression level (no/low vs. high) in HGNET, the other mechanisms except for proliferation, including SCLC-phenotype/NSCLC-phenotype or YAP1 expression, might explain the differential clinicopathological differences according to the TROP2 expression level in HGNET.