Histopathological aspects of cutaneous erythematous-papular eruptions induced by immune checkpoint inhibitors for the treatment of metastatic melanoma.

BACKGROUND: Immune checkpoint blockade therapy (ICBT) for the treatment of melanoma has led to an important improvement of overall survival in advanced stage patients. However, secondary cutaneous maculopapular eruptions (CMPEs) are frequent and remain poorly characterized. METHODS: We performed a retrospective analysis of melanoma patients from our institution who developed CMPEs during ICBT. Clinical information was retrieved, and histopathological and immunohistochemical characterization was performed by two pathologists. For comparison, a group of biopsies from CMPE caused by anti-v-raf murine sarcoma viral oncogene homolog B1 (BRAF) therapy was analyzed. RESULTS: Eleven patients met the inclusion criteria. On clinical grounds, CMPE developed mainly on early onset of immunotherapy and were of low grade. Typical lesions included erythematous papules and macules affecting the trunk and/or extremities with associated pruritus. The histopathological patterns consisted of a superficial perivascular lymphocytic dermatitis (SPLD) with eosinophils followed by a granulomatous dermatitis. Other patterns included lichenoid, spongiotic, and a case of Grover's disease. The inflammatory infiltrate consisted of T lymphocytes (CD3+ ) with a predominance of CD4+ over CD8+ cells; isolated Foxp3+ cells were invariably present, and PD-1 was not expressed. Biopsies from CMPE caused by anti-BRAF therapy showed an SPLD and a similar lymphocytic immunophenotype. CONCLUSIONS: Our study showed the clinical features of a group of melanoma patients with CMPE for ICBT and emphasized the wide spectrum of histological findings as well as their immunohistochemical profile. Differential diagnosis can be difficult with CMPE provoked by other therapies as was seen in our comparison group of anti-BRAF-induced eruptions.