Abstract PO2-17-10: Metaplastic breast cancer: description of 16 cases treated at a reference center and review of the literature
Authors: Mattar Andre , Antonini Marcelo , Diogenes Marina , Amorim Andressa , Cavalcante Francisco Pimentel , Gebrim Luiz Henrique 
Published: May 2024

Abstract
Background: Metaplastic breast carcinomas (MBC) are very rare and represent less than 1% of all invasive breast carcinomas. It is a heterogeneous neoplasm characterized by a mixture of adenocarcinoma with other histological elements such as squamous cells, spindle cells or other mesenchymal differentiation. Most MBC are hormone receptor and Her2 negative and tend to have a worse prognosis when compared to triple negative carcinomas. Clinically, they manifest as a rapidly growing palpable mass, without necessarily involving lymph nodes. According to the nomenclature of the WHO Classification of Tumors of the Breast (2012), tumors were classified into 4 variants: spindle cell, squamous cell, mesenchymal and mixed. Since publications on MBC are scarce in the literature, we studied the cases that were attended at Hospital Pérola Byington in the period 2010-2021. Methods: A retrospective study was carried out by reviewing the medical records of patients treated at the Reference Center for Women's Health - Pérola Byington Hospital, São Paulo, Brazil. Patients with breast cancer, with anatomopathological result confirming the diagnosis of metaplastic carcinoma were reviewed. Clinical data and histopathological characteristics were evaluated, as well as the type of treatment performed and the evolution. Results: A total of 16 female patients diagnosed with MBC were included. The median age was 56 years (ranging from 34 to 88). The mean initial size observed was 7 cm (ranging from 2 to 20 cm) and 94% of patients presented with a palpable mass. The initial clinical staging were I (12%), II (32%), III (50%) and IV (6%). The most common histological subtype was spindle cell (50%), of which 2 were squamous (12%), 3 mesenchymal (20%), 1 mixed spindle/squamous (6%) and 2 were not classified. Regarding immunohistochemistry, 14 patients (88%) had hormone negative and Her2 negative (triple negative). Of the 16 cases, 8 underwent mastectomy and 6 partial mastectomiy and 2 patients did not undergo surgical treatment because they died despite treatment with neoadjuvant chemotherapy. All operated patients underwent sentinel lymph node biopsy or axillary dissection and 85% of them did not have axillary lymph node involvement. Radiotherapy was indicated in 13 patients. Chemotherapy was performed in 10 patients, 6 of which were neoadjuvant (since the tumors were not resectable) and 4 received adjuvant chemotherapy. Of the 6 patients that underwent neoadjuvant chemotherapy, 2 had disease progression, 3 partial response and 1 complete pathological response. During follow-up, 4 (25%) evolved with locoregional recurrence and 5 (31%) with metastatic disease. Of these women, 44% (7) are still alive. We also found that 6 of the 16 cases (37%) did not receive a diagnosis of MBC in the initial biopsy, requiring revision, a new biopsy or study of the surgical specimen for confirmation. Conclusion: As verified in the literature, MBC is a very rare histological type and corresponded to 0.2% of all cases of breast cancer in the period described above. Most patients have an advanced tumor at the time of diagnosis and little axillary involvement. The most common histological classification is the spindle cell variant and almost all tumors are triple negative. The CMM has an aggressive behavior and little response to chemotherapy treatments. Therefore, radical surgical treatments are preferred. Due to the rarity of this entity there is little data published in the international literature.
Citation Format: Andre Mattar, Marcelo Antonini, Marina Diogenes, Andressa Amorim, Francisco Pimentel Cavalcante, Luiz Henrique Gebrim. Metaplastic breast cancer: description of 16 cases treated at a reference center and review of the literature [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 PO2-17-10.