Abstract

Pembrolizumab, a humanized IgG4 monoclonal antibody against programmed death 1 (PD-1) receptor, has been used for its antitumor activity against many cancers including melanoma, head and neck cancers, and non-small cell lung cancer (NSCLC). Known dermatologic side effects include Stevens - Johnson syndrome (SJS), Toxic Epidermolysis Necrolysis (TEN), pruritus, and vitiligo. Less familiar are reports of Pembrolizumab associated pseudoepithleliomatous hyperplasia, lichenoid dermatitis and eruptive keratoacanthomas. We add to this literature and report a 73 year old female woman with Stage IV NSCLC who, after two years of consistent Pembrolizumab use, developed an atypical squamous proliferation with overlapping features of hypertrophic lichen planus and early keratoacanthoma. The patient, who had a medical history of COPD and a 35 pack year smoking history, was found in late 2020 to have right sided NSCLC with bone metastases. The PD-L1 tumor proportion was 95% but with no other targetable mutations. She was placed on palliative radiotherapy and Pembrolizumab for a 13-month span without any dose limiting toxicities. However, at this time, she began developing well-circumscribed round hyperkeratotic papulonodules on her lower extremities. The lesions were tender to palpation and mildly pruritic. A biopsy revealed acanthosis of the epidermis with large glassy keratinocytes, necrotic keratinocytes and parakeratosis but without prominent hypergranulosis. Patient was placed on topical Clobetasol for several weeks with improvement. Herein, we present a case of a rare dermatologic side effect of Pembrolizumab that, although presents with features concerning for squamous cell carcinoma, can be successfully treated with topical corticosteroids.

Financial Disclosure:
No current or relevant financial relationships exist.