A 67-year old man is presenting a 1 cm nodule on the left back. No past history of malignancy.

    A 67-year old man is presenting a 1 cm nodule, which began growing fast for 3 months on the left back. He does not have any past history of melanoma.

    Staging and F/U: He underwent a staging evaluation with an MRI of the brain and a CT scan of the chest, which showed no evidence of metastasis of melanoma. He subsequently received a wide excision of the biopsy site and a dissection of sentinel lymph nodes, which were all negative for melanoma.

    Pathologic findings: Sections showed an invasive amelanotic melanoma with balloon cell morphology in the dermis. Prominent tumor infiltrating lymphocytes were noted. The melanoma cells showed a large balloon cell morphology with small to large atypical nuclei with occasional mitosis. No obvious in situ lesion was identified. Immunohistochemical studies showed that the tumor cells were positive for S100, MART-1, and HMB45 and negative for CD68. Findings support the melanocytic origin. Ki67 highlighted more than 50% of tumor nuclei, indicating as a high cell proliferative activity.