Hidden in plain sight: umbilical melanoma

A 74‐year‐old Caucasian woman was referred for hirsutism over the abdomen and was incidentally found to have a 21 × 25 mm ulcerated nodule over the umbilicus (Box 1). This occurred on the background of a longstanding lesion. Over the previous 6 months, the nodule had become ulcerated and occasionally bled. The remainder of the full skin examination was unremarkable, with no concerning lesions or palpable regional lymphadenopathy. She had no previous malignancy but had a strong family history of colorectal, breast, lung and pharyngeal cancer. Results of investigations to exclude internal malignancies were normal. Following an initial incisional biopsy demonstrating malignant amelanotic melanoma, a subsequent wide local excision confirmed this to be a stage IIIC, extensively ulcerated invasive nodular melanoma of 21 mm thickness and Clark level IV, with a mitotic rate of up to 15/mm². There was no lymphovascular or perineural invasion. Microsatellites, desmoplasia and regression were not identified. The melanoma was BRAF negative on both immunohistochemical and molecular testing. Sentinel lymph node biopsy showed two metastatic melanoma deposits in the left inguinal sentinel node. Initial staging evaluations showed no evidence of nodal or distant metastases on whole body positron emission tomography–computed tomography (PET–CT) and brain magnetic resonance imaging (MRI). The patient was commenced on adjuvant nivolumab immunotherapy, but 4 months into treatment was confirmed by biopsy to have recurrent left inguinal nodal metastatic disease, and a repeat PET–CT scan showed possible in‐transit metastasis in the abdominal wall. Dissection of the involved ilioinguinal lymph node and ultrasound‐guided removal of the abdominal metastatic deposit were being planned at the time of writing.