Abstract PO5-21-01: Carcinoma en cuirasse- a rare, but striking, cutaneous manifestation of metastatic breast cancer

Abstract Introduction: Carcinoma en cuirasse is a rare cutaneous metastatic presentation most commonly arising from primary breast cancers, typically after mastectomy. It appears like cellulitis and later develops into thickened rough patches of skin and even nodules. Carcinoma en cuirasse holds a poor prognosis, and treatment is difficult. Chemotherapeutic agents are unable to reach the tumor cells necessary, and radiation is ineffective because of skin curvature. Case Presentation: We report a female in her 70s with prior history of left breast ductal carcinoma in situ status post-radiation and lumpectomy, who presented with skin thickening of the left breast and solid masses in bilateral breasts 10 years later. Biopsy showed invasive ductal carcinoma of left breast (estrogen receptor [ER]/progesterone receptor positive [PR], human epidermal growth factor receptor-2 [HER2] negative) and ductal carcinoma in situ of right breast (ER/PR positive). She underwent right breast lumpectomy; however, the left breast mastectomy was aborted due to worsening of her skin findings on preoperative examination. An excisional skin biopsy revealed poorly differentiated invasive ductal carcinoma involving the dermis, deep dermis and focally involving the epidermis. Her diagnosis changed to stage 4 breast cancer, specifically carcinoma en cuirasse. Systemic treatment was initiated with palbociclib and letrozole and subsequently, she underwent left breast mastectomy given an excellent response to initial therapy. Surgical biopsy interestingly was HER2 positive and therefore her regimen was changed to taxotere, trastuzumab and pertuzumab. She completed adjuvant treatment and has been on maintenance trastuzumab along with letrozole currently and is doing well 5 years later with negative PET scans. Discussion: Our case is unique due to diagnosis of carcinoma en cuirasse before mastectomy, change in HER2 receptor status during treatment and excellent response to therapy with ongoing response to date. We think that an early diagnosis as well as targeted treatment could be the possible reasons for prolonged survival of more than 5 years. Conclusion: Any unexplained skin findings in breast cancer patients should prompt consideration of carcinoma en cuirasse. With ongoing treatment advances, many newer therapy options are available for metastatic breast cancer. Based on our case, we think that patients with this disease can have better outcomes. Citation Format: Manasi Godbole, Kashmira Wani, Shereen Zia, Vrushali Dabak. Carcinoma en cuirasse- a rare, but striking, cutaneous manifestation of metastatic breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-21-01.