An atypical presentation of Pembrolizumab-induced bullous pemphigoid in a patient with uterine serous carcinoma

Background: Immune checkpoint inhibitor-induced bullous pemphigoid (ICI-BP) is a rare but recognized complication of immune checkpoint inhibitor therapy. Compared to conventional BP, ICI-BP can present atypically, leading to delayed diagnosis and treatment, which can devastate quality of life for cancer patients. Literature on the presentation, diagnosis, and management of ICI-BP in patients with gynecologic cancer is scarce. Case Presentation: We report a case of ICI-BP presenting as erythema multiforme (EM)-like lesions in a woman in her early 60s with stage IVB uterine serous carcinoma. Upon diagnosis, the patient was treated with neoadjuvant carboplatin/paclitaxel followed by debulking surgery, adjuvant chemotherapy, and maintenance pembrolizumab immunotherapy. Pembrolizumab was discontinued after four cycles due to uveitis. Two months thereafter, she acutely developed painful oral mucosal erosions and a progressive palmoplantar eruption composed of targetoid and pseudo-targetoid plaques, leading to limited mobility and oral intake. Initial clinical evaluation favored EM, for which she began empiric antivirals and high-potency topical corticosteroids. Dermatology performed a skin biopsy which supported the diagnosis of ICI-BP with concomitant EM secondary to varicella zoster reactivation. The patient improved with systemic and topical corticosteroids followed by dupilumab as maintenance therapy. She was able to taper off systemic corticosteroids without recurrence of BP in eight weeks from rash onset. Conclusion: This case report exemplifies a delayed-onset, atypically presenting instance of ICI-BP in a patient with uterine serous carcinoma, and substantiates the utility of dupilumab as a steroid-sparing option for ICI-BP.