Hidden in plain sight: umbilical melanoma

Clinical record

Patient 1

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.

Patient 2

A 44‐year‐old Caucasian woman was referred for evaluation of an umbilical nodule, which had been bleeding following cryotherapy to the nodule 2 months earlier (Box 2). The nodule had been present for several years but enlarged over the past 12 months. She had a background of numerous dysplastic naevi but no history of melanoma. No palpable lymphadenopathy was detected. An initial excisional biopsy confirmed a stage IIB, ulcerated superficial spreading melanoma of 2.2 mm thickness and Clark level IV, with a mitotic rate of 7/mm². There was no evidence of satellitosis, regression, or lymphovascular or perineural invasion. The patient subsequently underwent a definitive wide local excision that revealed no residual melanoma and a sentinel lymph node biopsy that was negative. Staging whole body PET–CT and brain MRI scans showed no metastases. She received 4‐monthly follow‐up for the first 2 years and 6‐monthly follow‐up during the third year. No adjuvant therapy was required and she remains in remission 3 years since the initial diagnosis.

Discussion

Our cases illustrate the need for careful evaluation of ulcerated umbilical nodules and a low threshold for skin biopsy. Primary umbilical melanoma is rare, representing about 5% of all umbilical malignancies.1 Of the 22 cases reported in English literature (to May 2019), similar to our cases, 32% (7/22) arose from pre‐existing umbilical naevi (Supporting Information).2,3,4 The prognosis of umbilical melanoma is poor, with at least 27% (6/22) of reported cases dying from metastases despite initial excision. The median Breslow thicknesses of both superficial spreading and nodular subtypes are thicker in umbilical melanoma (2.2 mm and 16 mm, respectively) compared with melanoma at other sites (0.6 mm and 2.6 mm, respectively).5 Diagnosis is usually delayed, with an average time to diagnosis of 17 months (it is noted that time to diagnosis was not defined in about one‐third of the cases); this is often due to difficulties in clinical recognition and obscuration of the lesion by sagging skin contributed by ageing and obesity. Dermatoscopic examination of the site is also often challenging.

The main differential diagnosis of an ulcerated umbilical nodule is umbilical metastasis from advanced intra‐abdominal or pelvic malignancy, eponymously referred to as Sister Mary Joseph nodule, and is estimated to be 20‐fold more common than primary melanoma at this site.1 Although the umbilicus represents only a minute portion of the abdomen, it is a potential site for metastases owing to vestigial anatomical connections with the peritoneum and abdominopelvic organs.6

The Australian melanoma guidelines7 recommend that a suspicious pigmented lesion should undergo a complete excisional biopsy with a 2 mm clinical margin. In carefully selected cases including difficult anatomical locations, partial biopsies may be appropriate but need to be interpreted with caution to minimise false negative results and understaging. Following establishment of melanoma diagnosis and thickness, wide local excision is recommended for definitive treatment. Sentinel lymph node biopsy should be considered at the time of wide local excision for all melanomas greater than 1 mm in thickness (≥ 0.8 mm with other high risk features) to provide optimal staging and treatment options. BRAF mutation testing is recommended for all patients with unresectable stage III–IV melanoma to stratify patients for type of adjuvant therapy and to determine their eligibility for clinical trials. While the guidelines recommend whole body PET–CT and brain MRI scans for patients with stage III melanoma with palpable nodal disease and above, it is generally routine in some centres to also perform these investigations for stage IIC and most stage III melanoma patients, especially before commencing adjuvant therapy. While these investigations are not typically indicated for stage IIB melanoma, the decision to perform staging scans in Patient 2 was based on its high risk umbilical site. The overall management of our two patients complies with current Australian practice and guidelines.

Box 1 – Patient 1: ulcerated umbilical amelanotic melanoma in an older woman

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Box 2 – Patient 2: umbilical melanoma in a middle‐aged woman initially treated with cryotherapy

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