Radiation-induced undifferentiated pleomorphic sarcoma of the breast: a rare but serious complication following breast-conserving therapy. A case report and literature review.

Background: Undifferentiated pleomorphic sarcoma (UPS) of the breast is an extremely rare, but aggressive subtype of sarcoma that can develop in radiotherapy (RT)-treated breast cancer patients. Due to the low incidence, there are many uncertainties regarding the adequate management of these tumors. We present a rare case of radiation-induced UPS in a 63-year-old woman who had undergone breast conserving therapy for invasive ductal carcinoma of the left breast, six years prior to presentation.

Case presentation: A 63-year-old woman presented with a rapidly growing left breast mass. She had been diagnosed with invasive ductal carcinoma of the left breast for which she underwent a left upper outer quadrantectomy and ipsilateral axillary dissection followed by RT, six years previously. During her routine oncologic follow-up, the mammography revealed a dense, nodular opacity with microcalcifications. The breast ultrasound (US) confirmed the presence of the nodule. US-guided fine needle aspiration biopsy was performed and the diagnosis of UPS was made, the reason for which the patient underwent wide local excision of the left breast.

Conclusion: The diagnosis of RT-induced UPS is challenging and often missed due to the low incidence, long latency period, unspecific imaging findings, and difficulties in clinical and histological detection of these lesions. These tumors should be considered in differential diagnoses of rapidly-growing breast masses in previously RT-treated breast cancer patients, as they can mimic the local recurrence of the primary tumor. Since the prevalence of breast-conserving surgery followed by RT has been increasing, the careful monitoring of at risk patients is of utmost importance, as UPSs are highly aggressive tumors associated with very poor outcomes.