High density of M2-macrophages in acral lentiginous melanoma compared to superficial spreading melanoma.

AIMS: Acral lentiginous melanoma (ALM) is the most common type of melanoma in people with darker skin phototypes. There is some evidence that the aetiology, pathogenesis, risk factors and natural history of ALM differ from those of superficial spreading melanoma (SSM). ALM behaves more aggressively than SSM, but the biological explanation for these differences remains unknown. The presence of one subtype of macrophages, termed M2-macrophage (M2-M), has been found to be related to local progression, metastasis and poor prognosis in several neoplasms. The aim of this study was to compare the density of M2-Ms in ALMs versus SSMs, and to examine whether or not the density of M2-Ms is associated with histopathological features predictive of adverse prognosis in cutaneous melanoma (CM), as well as development of metastasis.

METHODS AND RESULTS: Sixty-seven ALMs and 67 SSMs cases were analysed. The tumours were classified according to thickness, ulceration, mitosis and metastasis. M2-M quantity was evaluated using immunohistochemistry with anti-CD163 and anti-CD206 antibodies. M2-Ms were increased in ALM compared with SSM, and were related to the histopathological features predictive of adverse prognosis in CM, such as thickness > 1.0 mm, ulceration and mitotic activity, and the development of metastasis.

CONCLUSIONS: Our study is the first, to our knowledge, to demonstrate the increased presence of M2-Ms in ALM compared with SSM. Our findings suggest that the increased M2-Ms in ALM are associated with the main histopathological features predictive of adverse prognosis in CM, as well as the presence of metastasis, and that these cells can be related to the aggressive behaviour seen in ALMs.