Mast Cells density in relation to recurrency, lymphovascular Invasion and MCPyV status in Human Merkel Cell Carcinoma: a descriptive study with prognostic implications

Abstract

Merkel cell carcinoma (MCC) is a rare, highly aggressive, primitive neuroendocrine carcinoma of the skin, the origin of which is not yet fully understood. Numerous independent prognostic factors have been investigated in an attempt to understand which are the most important parameters to indicate in the histological diagnostic report of MCC. Of these, mast cells have only been studied in one paper before this one. We present a retrospective descriptive study of 13 cases of MCC, received at the Department of Pathology over a 20-year period (2003–2023 inclusive) on which we performed a study using whole-slide (WSI) morphometric analysis scanning platform Aperio Scanscope CS for the detection and spatial distribution of mast cells, using monoclonal anti-Tryptase antibody and anti-CD34 monoclonal antibody to study the density of microvessels. Furthermore, we performed immunohistochemical reactions for MCPyV to split the study cohort of MCC in related and not-related to MCPyV. We found a statistically significant relationship between mast cell density in samples from patients who had experienced local recurrence/distant metastasis or death from MCC and patients who at follow-up (24 months) had shown no recurrence of disease (7.35 vs 2.5; p = 0.008). Regarding MCPyV status, we described for the first time (to the best of our knowledge) that MCPyV-negative MCC have more density of mast cells respect to MCPyV-positive MCC that are known to behave in less aggressive fashion. Conversely, no significant difference was observed between the median vascular density observed on excisional biopsy of patients experiencing recurrence or metastasis and the median observed on excisional biopsy of patients without recurrence (5.3 vs 1.7; p = 0.18). This paper, despite the sample size (n = 13), supports the inclusion of a semi-quantitative analysis of mast cell distribution and density in the histopathological report of MCC.