Abstract Carcinoma en Cuirasse (CeC) and Radiation-Induced Morphea (RIM) are two discrete and rare diagnoses, most commonly found among patients treated for breast cancer. Due to their similar clinical presentation and extremely low incidence rates, it can be challenging for providers to differentiate the pathologies promptly and accurately. Both pathologic processes result in sclerotic skin plaques with fibrotic changes to the dermis and subcutaneous tissue. Timely diagnosis is critical due to the high mortality rate of CeC and the potential reversibility of RIM if treated promptly. For this reason, improved patient care is dependent on increased awareness of how to distinguish these pathologies. In CeC, metastatic cells invade and disseminate via the superficial lymphatic vessels. The tumor cells are visualized in pattern of single-file lines, poorly differentiated, with atypical nuclei. There are hyperpigmented, indurated, and sclerotic plaques as well as firm, erythematous papules. The surrounding tissue is fibrotic with reduced vascularity. This fibrosis inhibits penetration of chemotherapy and can reduce efficacy of systemic therapies. Management is dependent on the cancer morphology and prompt initiation of the next line of therapy is recommended. RIM presents with erythema which progresses to sclerotic plaques and ultimately irreversible fibrosis of the dermis and subcutaneous tissue. Treatment consists of topical corticosteroids and calcineurin inhibitors for early stages, progressing to systemic treatment of immunosuppressants such as mycophenolate mofetil and methotrexate if needed. Retrospective analysis has shown that methotrexate or UVB phototherapy have achieved the best results. Citation Format: H. Grace, R. Assadi, N. Wandrey, M. Arbab, A. Rahimi. Carcinoma en Cuirasse and Radiation-Induced Morphea abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS5-06-28.
Grace et al. (Tue,) studied this question.