PD-1 Inhibitor Induced Hypertrophic Lichen Planus: A Case Study

PD-1 inhibitors have revolutionized the treatment of cancer and are being employed to treat an expanding array of cancers. Therefore, to best serve our patients, we must familiarize ourselves with the spectrum of skin manifestations associated with PD-1 inhibitor therapy. We report a unique case of hypertrophic lichen planus in a 64-year-old male treated with pembrolizumab that initially presented with a keratoacanthoma (KA) morphology before evolving into a more typical hypertrophic lichen planus. The patient had symptoms of mucositis for 4 months until nodules and plaques began emerging on his shins and dorsal hands, at which time the patient was referred to dermatology. Initial biopsy of shin nodule looked histologically compatible to a keratoacanthoma with lichenoid inflammation. Mohs surgery was performed on the patient's hands due to concerns of functional impairment. However, the lesions within the surgical site recurred rapidly. Repeat biopsy was performed of both the hand and the shin. Histopathology revealed features consistent with hypertrophic lichen planus. By this time, lower extremity lesions that initially appeared as KA-like had progressed to a more typical appearing hypertrophic lichen planus. Therapy was started with topical clobetasol and acitretin. All lesions resolved within 1–2 months. This case highlights the importance of maintaining a high suspicion for lichenoid reactions as sequelae to PD-1 inhibitors and displays how these reactions do not always present in their classical forms initially, and can transform over time.