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Since their first approval 25 years ago, monoclonal antibodies (mAbs) have become important targeted cancer therapeutics. However, dermatologic toxicities associated with non-immune checkpoint inhibitor (non-ICI) mAbs may complicate the course of cancer treatment. Data on the incidence and types of these reactions are limited.A comprehensive review was conducted on dermatologic toxicities associated with different classes of non-ICI mAbs approved for treatment of solid tumors and hematologic malignancies. The review included prospective Phase 1, 2, and 3 clinical trials; retrospective literature reviews; systematic reviews/meta-analyses; and case series/reports.Dermatologic toxicities were associated with several types of non-ICI mAbs. Inflammatory reactions were the most common dermatologic toxicities, manifesting as maculopapular, urticarial, papulopustular/acneiform, and lichenoid/interface cutaneous adverse events (cAEs) with non-ICI mAbs. Immunobullous reactions were rare and a subset of non-ICI mAbs were associated with the development of vitiligo cAEs.Dermatologic toxicities of non-ICI mAbs are diverse and mostly limited to inflammatory reactions. Awareness of the spectrum of the histopathologic patterns of cAE from non-ICI mAbs therapy is critical in the era of oncodermatology and oncodermatopathology.

The discovery of immune checkpoint inhibition (ICI) sparked a revolution in the era of targeted anticancer therapy. However, although monoclonal antibodies targeting the cytotoxic T-lymphocyte antigen-4 and programmed death-1 axes have improved survival in patients with advanced cancers, these immunotherapies are associated with a wide spectrum of dermatological immune-related adverse events (irAEs), ranging from mild to life-threatening. Several publications have addressed the clinical and histopathological classification of these skin-directed irAEs, their impact on anti-tumour immunity and survival, and the critical role of supportive oncological dermatology in their management. In this paper, we review the current understanding of the mechanistic drivers of immune-related skin toxicities with a focus on inflammatory, immunobullous and melanocyte/pigment-related reactions. We detail the specific immune-based mechanisms that may underlie different cutaneous reactions. We also discuss potential mechanisms as they relate to extracutaneous irAEs and the lessons learned from these, the potential overlap with cutaneous irAEs, techniques to study differences in immune-related vs. de novo skin reactions, and how treatment of these AEs impacts cancer treatment, patient quality of life and overall survival. An improved understanding of the mechanistic basis of cutaneous irAEs will allow clinicians to develop and use blood-based biomarkers that could help ultimately predict onset and/or severity of these irAEs, and to implement rational mechanistic-based treatment strategies that are targeted to the irAEs while potentially avoiding reducing the anti-tumour effect of ICIs.

A 65-year-old man with diabetes, end-stage renal disease on hemodialysis, coronary artery disease, and a prosthetic aortic valve. He presented to the emergency department with hypothermia (96.6°F), several weeks of anorexia and chills, and bilateral lower extremity tissue necrosis with erythema and edema (Figure 1A). He had a peripherally inserted central catheter (PICC) line 8 weeks prior placed at another hospital for treatment of cellulitis. Laboratory results revealed anemia, azotemia, and leukocytosis (19,200 WBCs/mm