Lymphatic invasion predicts aggressive behavior in melanocytic tumors of uncertain malignant potential (MELTUMP).

Lymphatic invasion (LI) identified by immunohistochemical (IHC) staining is common in primary cutaneous melanoma, and LI has been shown to be an independent prognostic factor in melanoma. Its prognostic significance in melanocytic tumors of uncertain malignant potential (MELTUMPs) has not been well characterized. This study included 32 patients with provisional diagnoses of MELTUMP. Lesions were evaluated for tumor thickness, the presence of ulceration, mitotic figures, mitotic figures at the base, tumor infiltrating lymphocytes, as well as peritumoral and intratumoral lymphatic density. Dual IHC staining was used to microscopically detect lymphatic endothelium (podoplanin) containing melanoma cells (S100), with the aid of multispectral imaging in select cases. Univariate analysis was performed to identify associations between clinical and pathologic variables and melanoma-related events. The 32 patients had a median follow-up of 111 months. Two patients subsequently died of melanoma-related disease, 1 died of unknown causes, 5 developed nodal metastases, and the remainder showed no evidence of progressive disease. LI was identified in 8/32 patients (25%) by dual IHC staining, which included the 2 patients who died of melanoma-related disease, 1 patient with bulky nodal metastasis, 1/4 patients with microscopic nodal metastases, and 4 patients who showed no evidence of progressive disease. The presence of LI was associated with melanoma metastases or melanoma-related death (P=0.05). The presence of LI by dual IHC in MELTUMPs is associated with a poorer prognosis, specifically with melanoma metastasis, and may therefore serve as a useful prognostic factor for risk stratification of patients with these diagnostically challenging lesions.