Huntingtin interacting protein 1 as a histopathologic adjunct in the diagnosis of Merkel cell carcinoma

Huntington interacting protein 1 (HIP1), an antiapoptotic protein normally expressed in the brain, is highly expressed in Merkel cell carcinomas (MCCs). Given this, the aim of the current study was to ascertain the value of HIP1 as a histopathologic adjunct in the diagnosis of MCC.

In this retrospective study, archival material from 26 cases with a diagnosis of MCC and/or neuroendocrine carcinoma were retrieved from the pathology files of the Skin Pathology Laboratory (Boston University School of Medicine, Boston, MA, USA). Histopathologic sections of all cases were re-reviewed and the diagnosis confirmed. All patient data were de-identified. Immunohistochemical studies were performed using antibodies to HIP1 and cytokeratins (CK) 20 and 7.

A semiquantitative scoring system for immunohistochemical expression of HIP1 was utilized by deriving a cumulative score (based on percentage positivity of cells and intensity of expression). Using a cut-off total score of 3 or more as positive, the total number of positive cases was 22 for HIP1, 24 for CK20, and 11 for CK7.

Comparing the results of HIP1 and CK20, there were four discordant pairs (three positive for CK20 but negative for HIP1 and one positive for HIP1 but negative for CK20). McNemar's test indicated that there was no statistical significance (P = 0.625), thereby implying a close agreement between the expression of HIP1 and CK20 in these neuroendocrine neoplasms.