Bullous Eruption Associated With Loncastuximab Tesirine in a Patient With Diffuse Large B‐Cell Lymphoma

ABSTRACT Loncastuximab tesirine (LT) is an antibody‐drug conjugate (ADC), a novel class of therapeutics that combines a target‐specific monoclonal antibody with a cytotoxic agent via a chemical linker. LT has been approved in the United States as therapy for relapsed or refractory diffuse large B‐cell lymphoma (DLBCL). Given the novelty of this drug, cutaneous adverse effects remain poorly characterized. In this case report, we present a 35‐year‐old male with relapsing and refractory DLBCL who developed a bullous eruption after his third cycle of LT. Physical exam revealed scattered erosions and erythema of the neck and extremities, along with multiple bullae and erosions on the hands and dorsal feet, and vesicles on the shin. Histopathological exam revealed basovacuolar alteration with epidermal dysmaturation and a re‐epithelializing blister, features suggestive of toxic erythema of chemotherapy (TEC). Direct immunofluorescence was negative for immune complex deposition. To date, there are only three cases of LT‐associated bullous eruptions in the literature, all demonstrating subepidermal blistering with granular IgA deposition along the basement membrane. This case lacks immunoglobulin deposition and instead exhibits TEC‐like cytotoxic interface dermatitis. This case expands the clinicopathologic spectrum of LT‐associated cutaneous toxicity and highlights a distinct non‐immune mediated, TEC‐like vesiculobullous presentation.