Pigmented eccrine poromas: expression of melanocyte-stimulating cytokines by tumour cells does not always result in melanocyte colonization

Background Although eccrine poroma (EP) occurs preferentially in palmoplantar areas, pigmented variants of EP have not been documented on the palms and soles. Objectives We seek to confirm the notion regarding lack of pigmented EP on palmoplantar areas and determine whether the absence of pigmentation in palmoplantar EPs is due to lack of expression of melanocyte‐stimulating cytokines by tumour cells. Methods We searched the PubMed and Web of Science databases (1966–2006) for reports of pigmented EPs. In addition, a total of 17 EPs were collected from our pathology department. The presence of melanin was examined with haematoxylin‐eosin sections, and melanocyte colonization was shown by immunohistochemical stains for tyrosinase. In addition, immunohistochemical staining with antibodies to melanocyte‐stimulating cytokines, including endothelin‐1, stem cell factor, and nerve growth factor, was done on these tumours. Results A review of the literature revealed 15 pigmented EP reports, none of which were located in palmoplantar areas. Among 17 EPs collected from our pathology department, 7 occurred in palmoplantar areas and 10 in non‐palmoplantar areas. Three of the palmoplantar EPs and three of the non‐palmoplantar EPs showed positive staining with melanocyte‐stimulating cytokines. However, none of the palmoplantar EPs contained melanocytes or melanin pigment, wheras the three non‐palmoplantar EPs that stained positively with melanocyte‐stimulating cytokines were colonized with melanocytes and showed pigmentation clinically. Conclusions The expression of melanocyte‐stimulating factors by tumour cells is associated with melanocyte colonization in non‐palmoplantar EPs but not palmoplantar EPs. Therefore, the presence of melanocyte‐stimulating cytokines per se is not sufficient by itself to induce melanocyte colonization. Certain characteristics of palmoplantar skin, such as the dermal components of these anatomical sites, may play a role in inhibiting melanocyte colonization of EPs.