PAS-positive loops and networks as a prognostic indicator in cutaneous malignant melanoma

Recently, microvascular channels, as detected by PAS histochemistry, were positively correlated with poor prognosis in uveal malignant melanoma. Since uveal melanomas are not penetrated by lymphatic vessels, while cutaneous melanomas are, the question arises as to whether these loops and networks are also of prognostic relevance in cutaneous melanoma. Histochemically and immunohistochemically detected loops and networks in 100 cases of cutaneous malignant melanoma were correlated with the occurrence of metastasis in a 10-year follow-up study. To detect these patterns, the significance of various methods (PAS reaction with/without nuclear counterstain, anti-laminin immunohistochemistry) was investigated. The presence of loops and networks was a highly significant prognostic marker (p<0.0001) for metastasis in cutaneous malignant melanoma. The presence of these patterns proved to have higher prognostic relevance for metastasis than Breslow's tumour thickness, especially for stage IB and stage IIA tumours (intermediate thickness/risk). PAS reaction without nuclear counterstain proved to be the best method to detect these patterns. Compared with the conventional staging of Breslow's tumour thickness, and especially so for stage IB and IIA melanomas, the determination of PAS-positive loops and networks in cutaneous malignant melanoma provides additional prognostic information.