ARRS 2022 Abstracts

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E1674. Imaging Features of Metaplastic Breast Carcinoma with Mesenchymal Differentiation
Authors
  1. Jane Shin; University of Texas MD Anderson Cancer Center
  2. Elsa Arribas; University of Texas MD Anderson Cancer Center
  3. Beariz Adrada; University of Texas MD Anderson Cancer Center
Background
Metaplastic carcinoma of the breast with mesenchymal differentiation (MCMD), previously known as carcinosarcoma, is a rare and aggressive malignancy. There are different subtypes of metaplastic carcinoma, with mesenchymal differentiation accounting for approximately 0.08–0.2% of all breast cancers. Metaplastic carcinomas are usually characterized by large size, lower rates of axillary nodal involvement, and high rates of triple negative breast cancer subtypes when compared to invasive ductal carcinoma. Additionally, metaplastic carcinomas may show more benign appearing imaging features when compared to invasive ductal carcinomas. Therefore, radiologists should be aware of this entity and associated imaging characteristics to avoid misdiagnosis, as this is an aggressive malignancy with poor prognosis and overall survival.

Educational Goals / Teaching Points
The purpose of this exhibit is to feature multimodality imaging characteristics of MCMD as well as key pathologic findings. Additionally, the radiologist should know when to include MCMD on the differential and what other diseases to consider. Current literature to date and management guidelines will also be reviewed.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
This educational exhibit will describe imaging characteristics of this uncommon entity across multiple imaging modalities including mammography, ultrasound, and MRI. Sample cases will be presented to highlight key imaging features. Histologically, MCMD consists of a mix of different mesenchymal components, including chondroid, osseous, rhabdomyoid, and rarely neuroglial elements. Most commonly, MCMD is seen as an admixture of cartilaginous and osseous differentiation. The unique pathophysiologic development and immunohistochemistry of this disease will be discussed. The radiologist should be aware of key imaging characteristics to communicate appropriate differential diagnoses to pathologists and clinicians to appropriately diagnose this disease.

Conclusion
MCMD is an aggressive tumor with high rates of distant metastases and poor prognosis. Given the uncommon nature of MCMD, it is critical that the radiologist can recognize this entity in order to guide appropriate workup, as MCMD has significant implications for patient management.