Solitary fibrous tumors (SFTs) are uncommon mesenchymal neoplasms that comprise <2 % of all soft tissue tumors. They are a diagnostically challenging group of neoplasms that can occur essentially anywhere. Molecular or genetic testing of soft tissue tumors will increasingly add to the foundation of distinctive histologic features, as accurate diagnosis is critical for appropriate treatment.
A 28-year-old woman was referred to our hospital for a left breast mass. Ultrasonography showed an oval hypoechoic mass with partially obscured boundaries. Surgical specimens revealed spindle tumor cells surrounding the mammary ducts and were immunoreactive for both CD34 and STAT6, suggesting SFTs. However, the infiltration of spindle tumor cells into the surrounding fat, and the storiform-like pattern made us consider dermatofibrosarcoma protuberans (DFSP) as a differential diagnosis. Lack of amplification of the COL1A1-PDGFB fusion gene, a characteristic feature of DFSP, led to our definitive diagnosis of breast SFT.
The presence of STAT6 in tumor cell nuclei is a highly sensitive immunohistochemical marker for SFT. In our case, morphological features evoked the differential diagnosis of DFSP and we investigated the COL1A1-PDGFB fusion gene. The diagnostic process of reliably performing careful morphological examination and immunohistochemical marker test, and then obtain conviction by molecular cytogenetic technique is more and more important for soft tissue tumors.
Solitary fibrous tumor arising at the breast is quite uncommon
Both solitary fibrous tumor and dermatofibrosarcoma protuberans are classified as fibroblastic/myofibroblastic soft tissue tumors
Solitary fibrous tumor is highly immunoreactive for STAT6
COL1A1-PDGFB fusion gene is a characteristic feature of dermatofibrosarcoma protuberans
Molecular cytogenetic technique would be required and be helpful for accurate diagnosis of soft tissue tumors