BI27 Eruptive naevi associated with encorafenib

Abstract

A 68-year-old farmer was referred for dermatology review after the sudden onset of numerous truncal naevi. He had a background of stage IV right-sided BRAF V600E-mutated colon cancer with nonoperable liver metastases. The patient underwent right hemicolectomy and stoma formation before commencing folinic acid–5-fluorouracil–oxaliplatin (FOLFOX)–Avastin chemotherapy. Given the burden of extensive metastatic disease, his chemotherapy regimen was switched to cetuximab and encorafenib. He developed over 100 darkly pigmented lesions within 6 weeks of treatment, in addition to the eruptive melanocytic lesions affecting the trunk, face and limbs. He had mucosal pigmentation. A biopsy of a representative lesion demonstrated a heavily pigmented, mildly atypical dysplastic naevus. He remains under observation after trametinib was added. The diagnosis of eruptive naevi associated with medications is contingent on a temporal relationship with specific medications, as well as development of one of the following: (i) 5 or more palmoplantar melanocytic naevi at any age, (ii) 10 or more melanocytic naevi at body sites outside of pregnancy or puberty and (iii) 20 or more melanocytic naevi during pregnancy or puberty. Encorafenib suppresses the RAS–RAF–MEK–ERK pathway in tumour cells expressing the p.V600E BRAF mutation. It has been demonstrated that treatment with BRAF inhibitors induces proliferation of wildtype BRAF cells in vivo. This promotes cell proliferation and survival, resulting in naevi of increased size and pigmentation. This case highlights the phenomenon of eruptive changing melanocytic lesions as an adverse dermatological toxicity of BRAF inhibitors.