Malignant Spindle Cell Tumor Breast—a Diagnostic Dilemma

Primary malignant spindle cell tumors are rare constituting 1.0% of breast malignancies. Spindle cell lesions occurring in soft tissues can occur in breast with overlapping morphologies. It can present as benign lesion and have inconclusive cytological findings, so easily missed if not properly dealt with. Stromal sarcoma should be diagnosed only after thorough sectioning and negative staining for p63, broad spectrum, and high molecular weight keratin. We present a case of right breast lump. Cytological features revealed fibro histiocytic lesion. There were no areas of necrosis, hemorrhage, or calcification. Histopathologically, it showed partially encapsulated tumor with cells arranged in sheets, composed of oval to epithelioid cells with spindling at places with moderate pleomorphism (mitotic activity 6–7/10 hpf). Differential diagnosis of primary stromal sarcoma, metaplastic sarcoma, and phyllodes was made. Immunohistochemistry revealed vimentin positivity with focal positivity of S-100. Desmin, cytokeratin and smooth muscle actin, p63, ER, PR, and Her2-neu were negative. A final diagnosis of primary breast sarcoma of neural origin was established with the help of histopathology and immunohistochemistry. To conclude, it is of utmost importance to identify primary stromal sarcomas as they are known to spread very rapidly and have a poor prognosis.