Persistent Diffuse Telangiectatic Eruption Associated With Loncastuximab Tesirine.

Loncastuximab tesirine (LT) is a CD19-directed antibody-drug conjugate approved for the treatment of relapsed or refractory diffuse large B-cell lymphoma. We report a case of a persistent, diffuse telangiectatic eruption that developed shortly after initiation of LT. Histopathologic examination revealed mild epidermal thinning with superficial ectatic vessels, large conspicuous fibroblasts, solar elastosis, and scattered dermal melanophages. This case highlights a distinctive, minimally inflammatory, vascular-predominant reaction pattern associated with LT. This morphology has been only recently recognized as a potential adverse effect of antibody-drug conjugate medications, with very few published literature on the subject. Because the use of antibody-drug conjugates continues to expand, recognition of this pattern is important, particularly given its persistence even after therapy cessation and limited response to corticosteroid treatment.