Myxofibrosarcoma: Outcomes, Prognostic Factors, and Role of Neoadjuvant Radiation Therapy.

PURPOSE: Myxofibrosarcoma (MFS) is a subtype of soft tissue sarcoma with a highly infiltrative growth pattern that leads to a higher risk of inadvertent positive surgical margins and local relapse. Poorly defined tumor margins also pose a challenge for radiation therapy (RT) planning, in terms of treatment volumes and administration of pre- versus postoperative RT. This study aims to evaluate local control and patterns of recurrence in patients with MFS treated with neoadjuvant RT followed by definitive surgical excision.

METHODS AND MATERIALS: Multiple institutional databases were retrospectively searched for patients diagnosed with MFS between 2013 and 2021 who were exclusively treated with preoperative RT followed by definitive surgery at our institution. The endpoints of the study were defined as local tumor recurrence, distant metastasis, and death after the date of definitive surgery.

RESULTS: Forty-nine patients met the inclusion criteria and were included in the final study. The median age at diagnosis was 67 years, and 71% of patients were male. The tumor was superficially located in 63% of patients, and the mean tumor size at presentation was 7.8 cm. All patients received neoadjuvant RT and completed their planned course of treatment. Neoadjuvant chemotherapy was administered in 22% of patients. Inadvertent excision (IE) before definitive treatment was performed in 25 patients (51%), 84% of which had superficially located tumors. All margins were assessed using frozen section analysis at the time of definitive surgery, and 100% of patients had negative surgical margins, with 25% having no residual tumor. With a median follow-up of 4.7 years, the 5-year local control rate was 87%, and 5-year overall survival was 98%. Tumor depth was associated with distant metastasis ( P < .01).

CONCLUSIONS: Despite the infiltrative nature of MFS, preoperative RT followed by definitive surgical excision, especially in the setting of a reliable frozen section margin analysis, was associated with excellent local control.