Usefulness of ulceration and hyperkeratosis as clinical predictors of Merkel cell polyomavirus-negative and combined Merkel cell carcinoma: A retrospective study

A review on the oncogenesis of Merkel cell carcinoma: Several subsets arise from different stages of differentiation of stem cell

Merkel cell carcinoma (MCC), a rare primary cutaneous neuroendocrine neoplasm, is extremely aggressive and has a higher mortality rate than melanoma. Based on Merkel cell polyomavirus (MCPyV) status and morphology, MCCs are often divided into several distinct subsets: pure MCPyV-positive, pure MCPyV-negative, and combined MCC. MCPyV-positive MCC develops by the clonal integration of viral DNA, whereas MCPyV-negative MCC is induced by frequent ultraviolet (UV)-mediated mutations, that are characterized by a high mutational burden, UV signature mutations, and many mutations in TP53 and retinoblastoma suppressor gene (RB1). Combined MCC consists of an intimate mix of MCC and other cutaneous tumor populations, and is usually MCPyV-negative, with rare exceptions. Based on the existing subsets of MCC, it is speculated that there are at least 4 stages in the natural history of stem cell differentiation: primitive pluripotent stem cells, divergent differentiated stem cells, unidirectional stem cells, and Merkel cells (or epidermal/adnexal cells). In the first stage, MCPyV may integrate into the genome of primitive pluripotent stem cells, driving oncogenesis in pure MCPyV-positive MCC. If MCPyV integration does not occur, the stem cells enter the second stage and acquire the ability to undergo multidirectional neuroendocrine and epidermal (or adnexal) differentiation. At this stage, accumulated UV-mediated mutations may drive the development of combined MCC. In the third stage, the stem cells differentiate into unidirectional neuroendocrine stem cells, UV-mediated mutations can induce carcinogenesis in pure MCPyV-negative MCC. Therefore, it has been speculated that several subsets of MCCs arise from different stages of differentiation of common stem cells.

Merkel cell carcinoma: A systematic review of the demographic and clinical characteristics of 847 cases in Japan

Merkel cell carcinoma (MCC) is a rare but aggressive neuroendocrine carcinoma of the skin associated with Merkel cell polyomavirus and immunosuppression. Although MCC incidence is rising worldwide, MCC has not been sufficiently investigated in Japan. This study aimed to determine MCC demographics in Japan, including incidence, age, sex, location, spontaneous regression, and pure/combined MCC. Using PubMed and Igaku Chuo Zasshi, 847 MCC cases between 1985 and 2015 were extracted, and the main epidemiological characteristics were described. The mean age of all patients was 77.5 years. Regarding the characterized lesions, 63.0% were located on the head and neck, 5.2% on the trunk, 12.6% on the upper limb, 15.1% on the lower limb, 3.5% on the buttocks, and 0.6% on the genitals. Histopathological information regarding the presence of other malignancies could be retrieved in 611 cases, and a coexisting malignancy, mainly squamous cell carcinoma and Bowen's disease, was present in 14.2%. Subcutaneous MCC was observed in 31 patients with a male : female ratio of 1.07 (16 men/15 women). Nodal lesions with unknown primary tumor location were described in 19 patients with a male : female ratio of 0.9 (nine men/10 women) and a mean age of 77.7 years. Of 640 evaluable cases, spontaneous regression developed in 9.1%. Among those 58 patients, the male : female ratio was 1:2.1 in 56 evaluable cases (18 men/38 women). Merkel cell polyomavirus was assessed in 180 patients, and the virus was detected in 31.1% and not detected in 68.9% of the patients. MCC is a rare disease in Japan, with incidence rates and male : female ratios differing from those in the USA and European countries. Besides, this study reveals the high frequency of subcutaneous MCC and MCC with divergent differentiation patterns and spontaneous regression in Japan compared to other countries.

Tumor Ulceration, Reduced Infiltration of CD8-Lymphocytes, High Neutrophil-to-CD8-Lymphocyte Ratio and Absence of MC Virus are Negative Prognostic Markers for Patients with Merkel Cell Carcinoma

(1) Background: Merkel cell carcinoma (MCC) is caused by the Merkel cell polyomavirus and UV radiation. Understanding of the underlying biology is limited, but identification of prognostic markers may lead to better prognostic stratification for the patients. (2) Methods: Ninety patients diagnosed with MCC (1996–2012) were included. Virus status was estimated by polymerase chain reaction (qPCR) and immunohistochemistry (IHC). Ulceration status, PD-L1, cd66b neutrophils, cd8 lymphocytes and biomarkers of vascularization (cd34 endothelial cells) and migration (e-cadherin) were estimated by IHC and analyzed with digital pathology. (3) Results: Virus was present in 47% of patient samples and correlated with lower E-cadherin expression (p = 0.0005), lower neutrophil-to-CD8 lymphocyte ratio (N:CD8 ratio) (p = 0.02) and increased PD-L1 expression (p = 0.03). Ulceration was associated with absence of virus (p = 0.03), increased neutrophil infiltration (p < 0.0001) and reduced CD8 lymphocyte infiltration (p = 0.04). In multivariate analysis, presence of virus (p = 0.01), ulceration (p = 0.05) and increased CD8 lymphocyte infiltration (p = 0.001) showed independent prognostic impacts on MCC-specific survival. (3) Conclusions: In this study, we found that a high N:CD8 ratio, ulceration, virus-negative status and absence of CD8 lymphocytes are negative prognostic markers. Accurate prognostic stratification of the patients may be important in the clinical setting for determination of adjuvant treatment.