Amelanotic Lentigo Maligna Melanoma: Mohs Surgery as the Definitive Treatment of an Invisible Tumour.

Amelanotic lentigo maligna melanoma represents <2% of melanomas. Diagnosis is delayed owing to the lack of lesion pigmentation and advanced disease at presentation. Excision with appropriate margins is the treatment standard, but the starting point for such margins is often unclear. We describe 2 patients with amelanotic melanoma treated by Mohs micrographic surgery (MMS) that would not have been cleared by wide local excision alone and provide an extensive review of the literature. Both patients presented with histologic diagnoses of malignant melanoma, one with a barely perceptible biopsy site scar on the left infraorbital cheek/lower eyelid (Breslow 1.8 mm) and the second with an amelanotic tumour on the right helix (Breslow 10 mm). Due to location, aggressive histology, amelanotic appearance, and no apparent surrounding skin surface changes, MMS was elected to maximise margin control. For patient 1, invasive and in situ tumour was found at the American Joint Committee on Cancer-recommended margin of 1.5 cm, and the final defect measured 8.5 × 4.8 cm. Patient 2 had a significant invasive and amelanotic lentigo maligna component, resulting in a 9.0 × 6.5-cm defect. MMS allows for immediate histologic feedback on tumour margins of a clinically invisible tumour and thus offers the most definitive treatment.