BI24 Cutaneous pseudolymphoma secondary to pembrolizumab

Abstract

Abstract A 35-year-old man presented with a 7-week history of itchy, nontender, indurated erythematous plaques and nodules on his forehead and upper back, with no discriminatory clinical features. He was systemically well. Three months previously, he had completed a 12-month course of adjuvant pembrolizumab for stage IIIC melanoma. The primary melanoma had been excised from his left cheek, with involvement of left parotid and supraclavicular lymph nodes, treated with clearance via superficial parotidectomy and left neck dissection. Clinical and imaging surveillance revealed no evidence of melanoma recurrence. Incisional biopsies of the lesions on his back and forehead both demonstrated a superficial and deep dermal perivascular and periadnexal infiltrate of small- and medium-sized lymphoid cells. There was no epidermotropism and B- and T-cell clonality studies were negative. Morphological appearance and immunophenotype favoured a CD4+-reactive lymphoid process in keeping with cutaneous pseudolymphoma (CPL), secondary to pembrolizumab. The conspicuous forehead lesion was unresponsive to clobetasol propionate under occlusion. A single course of intralesional triamcinolone acetonide 10 mg mL–1 resulted in significant improvement within days, with subsequent complete resolution. The lesion on the back resolved spontaneously. Drug-induced CPL describes an adverse cutaneous drug reaction mimicking B- or T-cell lymphomas clinically and/or histologically. It has been described with anticonvulsants, antidepressants and biologic agents, often with resolution on cessation of the responsible drug (Etesami I, Kalantari Y, Tavakolpour S et al. Drug-induced cutaneous pseudolymphoma: a systematic review of the literature. Australas J Dermatol 2023; 64:41–9). It has been proposed that the drugs affect immune surveillance, leading to an abnormal cutaneous lymphocyte response. A case report (Ayoubi N, Haque A, Vera N et al. Ipilimumab/nivolumab-induced pseudolymphoma in a patient with malignant melanoma. J Cutan Pathol 2020; 47:390–3) has described drug-induced CPL secondary to ipilimumab and nivolumab in a 38-year-old man presenting with erythematous plaques on the hands and face, similar to the presentation of our patient, which responded to prednisolone. As with the other adverse effects of immunotherapy, it is likely that CPL in this cohort is due to an iatrogenic immune dysregulation leading to T-cell overactivity. We present the first reported case of CPL secondary to pembrolizumab and highlight the successful use of intralesional steroid as a treatment option. It is important to recognize CPL as an adverse cutaneous effect of immunotherapy and be aware that it can present after completing treatment due to an ongoing immune response.