Heterogeneous Intermediate Phenotypes of Cancer Cells with Varying Ki-67-Positivity Rates, Including Histologically HCC-like and NEC-like Cells, in Liver MiNEN.

Mixed hepatocellular carcinoma (HCC)-neuroendocrine carcinoma (NEC) is a major type of liver mixed neuroendocrine-non-neuroendocrine neoplasm (MiNEN). Primary liver NEC, which is very rare, is mostly associated with HCC rather than pure NEC. To characterize the cancer cell heterogeneity of the HCC and NEC components, we comprehensively analyzed the protein expression of three cancer cell biological markers (TERT, Ki-67, and p53) and five differentiation markers (one hepatocyte marker and four neuroendocrine markers) via immunohistochemistry and immunofluorescence using curative resection tissues from three patients with liver MiNEN. TERT/Ki-67/p53 proteins, which are related to cell proliferation and malignancy, were independently expressed in the HCC and NEC components; Ki-67 was highly expressed among the three proteins in both cancer components, and the expression of all three markers was higher in the NEC component than in the HCC component. Despite the intracomponent and intercomponent heterogeneity, the expression signatures of the three markers were similar between the two components, potentially suggesting a common origin of mixed HCC-NEC. An in-depth exploration of intracomponent heterogeneity using differentiation markers revealed multiple intermediate phenotypes of cancer cells, i.e., HCC-like and NEC-like cells, mainly in the HCC component. Histologically NEC-like cells rather than HCC-like cells tended to have an intermediate percentage of Ki-67-positive cells, compared with NEC cells. The spatial distribution of various intermediate cancer cell phenotypes suggests that mixed HCC-NEC may involve the transdifferentiation from HCC cells to NEC cells through the dedifferentiation of HCC.