Molecular characterization of pleomorphic liposarcomatous differentiation in malignant phyllodes tumor of the breast: A case report.

Phyllodes tumors of the breast are rare fibroepithelial tumors, and malignant phyllodes tumors occasionally exhibit heterogeneous differentiation. Here, we report a case of malignant phyllodes tumor with pleomorphic liposarcomatous differentiation, and examined the genomic features of both components using capture-based next-generation sequencing of 425 cancer-related genes. A 56-year-old woman presented with a palpable, asymptomatic nodule in the right breast measuring 4.0 cm × 3.0 cm. Based on the findings from microscopic examination, the lesions were identified as malignant phyllodes tumor and pleomorphic liposarcoma. The liposarcomatous differentiation component was positive for S-100, but had no MDM2 and CDK4 amplifications according to the results of fluorescence in situ hybridization. The malignant phyllodes tumor and liposarcomatous differentiation component had similar genetic mutations, such as TP53, TERT, EGFR, RARA, RB1, and MED12 mutations, all of which are common mutations in phyllodes tumors. These results indicate that the pathogenesis of the pleomorphic liposarcomatous differentiation was similar with that of phyllodes tumor, but was different from the pleomorphic liposarcoma in extramammary sites. Thus, the intratumoral heterogeneity may have independently evolved after tumorigenesis.