We examined the role of mast cell infiltrates and other clinical and histological factors in the prognosis of Merkel cell carcinoma. Mast cells were stained immunohistochemically in 36 Merkel cell carcinomas with an antibody to tryptase. The number of stainable cells was quantified within the tumors and surrounding stroma. Other clinical and histological parameters were examined, statistically analyzed, and compared to subsequent clinical course and prognosis. Patient prognosis was worse with higher tumor mast cell numbers (P < 0.002). Prognosis was also found to be adversely affected by the presence of lymphovascular invasion (P = 0.03) and increased tumor size (P = 0.05). Increased mast cells counts, tumor size, and lymphovascular invasion are associated with an adverse prognosis in Merkel cell carcinomas. Evaluation of mast cell infiltrates may provide useful prognostic data and ultimately could assist in selecting patients that require adjuvant treatment in this aggressive form of skin cancer.

Merkel cell carcinomas are aggressive tumours for which histological prognostic factors need to be established. This study examines the prognostic role of vascular density, based on CD34 immunohistochemical staining in Merkel cell carcinoma. Thirty-six cases of Merkel cell carcinoma were immunohistochemically stained for the endothelial marker CD34. Vascular density was assessed in the tumor and stroma with a Chalkley eyepiece graticule. The scores of vascular density were correlated with other clinical and histological parameters to determine the prognostic significance of tumor vascularity. Increased vascular density was shown to be significantly associated with a worse prognosis (P = 0.005). A 1-unit increase in total vessel score was associated with a 3.9 times increase in the risk of death (95% hazard ratio confidence limits 1.50-10.32). Other factors associated with a worse outcome included tumor size (P = 0.05), the presence of lymphovascular invasion (P = 0.03), and tumor mast cell count (P < 0.002). Increased vascular density is associated with a worse prognosis in Merkel cell carcinomas. Assessment of vascular density may assist in predicting clinical behavior in these tumors and in evaluating the effects of adjuvant therapy.

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IntroductionThe authors present a form of dermatofibroma rarely seen and described, with a clinical appearance of giant plaques accompanied by satellite lesions.Case reports Unusual giant dermatofibromata are reported in a 40-year-old man and a 48-year-old man, who both presented with plaques on a lower limb. The largest plaque in each case was well-defined, reddish brown, indurated and measured 50 mm ¥ 30 mm and 70 mm ¥ 40 mm, respectively. Several satellite lesions were present around the large plaques. Dermoscopic examination showed diffuse homogenous pigmentation in the absence of other diagnostic criteria for dermatofibroma.Histology Light microscopy of biopsies from each patient displayed dermal proliferation of fibrohistiocytic cells, with a storiform dermal proliferation of spindle cells of bland appearance, and entrapped intervening collagen bundles. The overlying epidermis was acanthotic and there was no evidence of malignancy. Immunohistochemical staining was positive for Factor XIIIa and negative for CD34. Based on the histological findings, a diagnosis of giant dermatofibroma was made for each of these cases. ConclusionThese cases represent extraordinary examples of giant dermatofibroma as the lesions were not pedunculated as reported in previous cases, 1,2 and also exhibited the uncommon feature of satellitosis. Fewer than 20 cases of giant dermatofibroma have been reported to date, and only one, which was histologically different to the present cases, has shown satellitosis and a plaque-like appearance. 3 The authors propose the term 'Plaque-like Dermatofibroma with Satellitosis' for this distinct clinical entity.

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