Metaplastic carcinoma is a rare form of breast carcinoma that comprises less than 5% of all breast malignancies (1, 2). These tumors are ductal carcinomas that can undergo a variety of metaplastic changes including squamous cell, spindle cell, and heterologous mesenchymal growth (3,4). The most common of these metaplastic changes is squamous metaplasia, and its incidence varies from 0.5 to 2.0% (5). The microscopic criteria for the diagnosis of the squamous component are defined as keratinization, intercellular bridges and cystic areas (3,4). Although there have been many reports about the radiologic findings of metaplastic breast carcinoma, to our knowledge, there have been few reports about the ultrasonographic (US) findings of metaplastic squamous breast carcinoma. Therefore, we described here the US appearance of metaplastic squamous breast 669 Purpose: We investigated the ultrasonographic (US) appearance of metaplastic squamous breast carcinoma with the pathologic correlation. Materials and Methods: During an 8-year period, the US appearances of 10 patients with metaplastic squamous breast carcinoma were retrospectively analyzed on the basis of the Breast Imaging and Reporting Data System (BI-RADS) -US lexicon. These 10 patients included 9 patients having invasive adenocarcinomas of the breast with more than 30% squamous metaplasia, and one patient had pure primary squamous cell carcinoma. We correlated the US findings with the pathologic findings. Results: On US, the majority of the tumors showed oval shapes (70%), indistinct margins (50%), parallel orientation (80%), echogenic halos (60%), complex echogenicity with solid and cystic components (60%), and posterior enhancement (70%). The findings of calcifications (20%) and metastatic axillary lymph nodes (10%) were rare. On pathologic examination, half of the tumors showed infiltrative microscopic margins. All six cases showing complex echogenicity with solid and cystic components on US were pathologically related to the cystic or necrotic portion, and three of these cases had hemorrhage. Conclusion: On US, metaplastic squamous breast carcinoma mainly manifested as oval, complex, echoic masses with indistinct margins and posterior enhancement that was pathologically related to the cystic or necrotic portions.
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