Acanthosis Nigricans in a Patient with Urothelial Carcinoma Treated with PD-L1 Inhibitor Avelumab, and Secondary Adrenal Insufficiency.

Acanthosis nigricans (AN) describes hyperkeratotic and hyperpigmented skin changes and its pathophysiology is linked to the activation of epidermal growth factor receptors. Current literature shows that AN is most commonly diagnosed at the time of the underlying pathology, which may occur under benign or malignant conditions. This case presentation demonstrates the occurrence of AN in a patient following the diagnosis of urothelial carcinoma and ongoing treatment with PD-L1 inhibitor immunotherapy. Subsequent investigations ruled out a secondary malignancy or disease progression; however, metabolic screening identified secondary glucocorticoid induced adrenal insufficiency. AN was persistent in this patient despite adequate treatment, which highlights its co-occurrence in both benign and paraneoplastic conditions.