05 Perioperative Radiotherapy for Malignant Phyllodes Tumors: Evidence Summary and Practical Considerations for Chest-Wall Interstitial HDR Brachytherapy

Background

Phyllodes tumors are rare fibroepithelial breast neoplasms, accounting for less than 1% of breast tumors, and are classified as benign, borderline, or malignant based on stromal cellularity, atypia, mitotic activity, and tumor borders. Despite surgical excision with negative margins, local recurrence rates of approximately 20% to 30% have been reported for borderline and malignant phyllodes tumors. Higher-grade phyllodes tumors exhibit malignant stromal behavior and infiltrative growth patterns overlapping biologically with soft-tissue sarcomas (STS), prompting consideration of sarcoma-based radiotherapy paradigms in selected high-risk clinical scenarios.

Materials and Methods

A narrative literature review was performed focusing on radiotherapy for borderline and malignant phyllodes tumors, including systematic reviews, consensus statements, and retrospective series. Foundational randomized studies evaluating radiotherapy for STS, along with American Brachytherapy Society guidance on interstitial high-dose rate (HDR) techniques, were reviewed to inform extrapolation of sarcoma-based, tumor-bed–focused radiation approaches.

Results

Evidence supporting radiotherapy for malignant phyllodes tumors remains limited and heterogeneous, with no randomized trials specific to this disease. Retrospective series and meta-analyses suggest that adjuvant radiotherapy may reduce local recurrence in borderline and malignant phyllodes tumors, particularly for large tumors (≥5 cm) or those with close or positive margins, though reported outcomes vary across studies. A recent Canadian modified Delphi consensus demonstrated no agreement on routine radiotherapy following mastectomy with negative margins, particularly for smaller tumors, reinforcing the need for individualized, multidisciplinary decision-making in high-risk or atypical presentations. In contrast, the role of radiotherapy in STS is well established. Randomized trials have demonstrated improved local control with postoperative interstitial brachytherapy compared with surgery alone, supporting focused tumor-bed irradiation using multicatheter techniques. These data provide a biologic and technical rationale for extrapolation to malignant phyllodes tumors, which share sarcomatous stromal behavior. Interstitial high-dose-rate brachytherapy enables delivery of an effective, highly conformal dose to the high-risk tumor bed while minimizing exposure to surrounding normal tissues. Importantly, this approach allows a short overall treatment duration compatible with staged reconstruction and complex chest-wall management. Prior breast and chest-wall brachytherapy reports have demonstrated technical feasibility and acceptable acute toxicity in similar contexts. Figure illustrates a surgery-first workflow integrating postoperative interstitial HDR brachytherapy in clinically constrained, high-risk cases.

Illustrative Institutional Experience

Institutional experience is presented to contextualize the reviewed literature. In clinically complex presentations where preoperative radiotherapy was not feasible, postoperative interstitial HDR brachytherapy enabled focused chest-wall irradiation while preserving options for staged reconstruction. This experience is presented for illustrative purposes and is not analyzed as a formal case series.

Conclusions

Radiotherapy for malignant phyllodes tumors remains supported by limited disease-specific evidence. When radiotherapy is selected for high-risk scenarios, such as large tumor burden or clinically constrained surgery-first presentations, extrapolation of sarcoma-based principles using multicatheter interstitial HDR brachytherapy represents a feasible strategy for targeted chest-wall irradiation. Further collaborative studies are needed to refine patient selection and long-term outcomes.