BI22 Anti-TIF1-γ-positive dermatomyositis associated with pembrolizumab-treated breast cancer

Abstract

Immune checkpoint inhibitors (ICIs) have transformed the management of solid organ malignancies but can trigger immune-­related adverse events (irAEs) affecting multiple organs, including muscle and skin. Dermatomyositis (DM) is a rare but increasingly recognized complication of ICIs. Late and post-treatment irAEs are recognized with ICIs, but cases of DM presenting following completed treatment and complete remission of malignancy are rare. We describe a case of anti-transcriptional intermediary factor (TIF)1-γ-positive DM arising after pembrolizumab therapy for ­triple-negative breast cancer in remission, to highlight diagnostic, therapeutic and mechanistic considerations. We conducted a detailed clinical, laboratory, radiological and histopathological evaluation of a 42-year-old woman presenting with cutaneous features of DM, 2 months following completion of ICI therapy. Autoantibody profiling, magnetic resonance imaging, tissue biopsy and malignancy surveillance, including computed tomography (CT), positron emission tomography–CT and colonoscopy, were performed. Treatment response to corticosteroids, immunosuppressive therapy and intravenous immunoglobulin (IVIg) was assessed. The presentation demonstrated classic features of DM including heliotrope rash, Gottron papules and proximal muscle involvement. Symptoms started 2 months after the patient completed seven cycles of pembrolizumab-based therapy for breast cancer, which was radiologically in remission. Investigations revealed positive antinuclear antibodies, mildly raised creatine kinase, magnetic resonance imaging-confirmed myositis, interface dermatitis on skin biopsy, and anti-TIF1-γ antibodies. No recurrent or new malignancy was detected. She had partial response to corticosteroids and mycophenolate mofetil. Subsequent initiation of IVIg achieved significant clinical improvement. This case of pembrolizumab-associated anti-TIF1-γ DM in a patient with breast cancer in remission adds to cases in the literature of ICI-induced DM, and in particular to those presenting after completed treatment of malignancy with ICIs. Clinicians should consider prior ICI exposure when evaluating new-onset DM, even after cancer treatment has concluded. Thorough malignancy screening remains essential, and awareness of delayed-onset ICI-related DM may improve diagnostic accuracy and management.