P167 Extensive café au lait melanocytic birthmarks with metastatic melanomas

Abstract

Patients with extensive café au lait (CAL) melanocytic birthmarks with variable speckling may develop metastatic malignant melanoma. This retrospective case note review was designed to report clinical and genetic data across three cases. A 47-year-old man presented with a naevoid malignant melanoma arising within a 22 × 10-cm CAL birthmark with dark speckles on his back (naevus spilus type). Aged 59 years, he re-presented with widespread meta­static melanoma, which he succumbed to within 6 months. Histology of a liver metastasis confirmed BRAF wildtype metastatic melanoma. A 77-year-old woman presented with three primary melanomas on the right leg, the first aged 57 years followed by two aged 77 years. All arose within an extensive CAL birthmark comprising light brown macules and darker brown melanocytic naevi involving the entire right leg. A somatic mutation in NRAS (c.34G>C) was detected within the birthmark. Within months, in transit metastases developed adjacent to the wider excision scar and were excised. At age 81 years, inguinal nodal metastasis and further cutaneous in transit metastases were detected, and were managed palliatively due to her performance status. A 14-year-old girl presented with a superficial spreading malignant melanoma on the right lower back. Sentinel lymph node biopsy identified bilateral inguinal nodal metastases. She had multiple 3–4-cm CAL macules on the right side of her torso, and ipsilateral axillary freckling. A pathogenic variant in SPRED1 (c.633del) was detected within the birthmark. While the primary melanoma demonstrated a somatic BRAF mutation (c.1799T>A), neither the primary melanoma nor lymph node samples demonstrated the SPRED1 variant. The patient received dabrafenib and trametinib, and is in remission after 3 years. Metastatic melanoma is an infrequent outcome in patients with melanoma arising within extensive CAL-type birthmarks. The genetic bases of these birthmarks are testable and diverse and may inform the selection of treatment in the event of metastasis.