101P Primary malignant phyllodes tumors of the breast: A retrospective analysis from a referral center

The treatment of primary malignant phyllodes tumors of the breast (B-MPT) consists of wide local excision with negative margins (≥1 cm). However, because of their rarity, prognostic factors, optimal type of surgery and adjuvant treatments are still a matter of debate. We conducted a single-center, retrospective study on the clinical outcomes and prognostic factors in patients with primary B-MPT, who underwent breast surgery from January 2000 to December 2021. The primary endpoint was the cumulative incidence of any recurrence. Secondary endpoints were the cumulative incidence of distant and local recurrences. 131 patients were included. All received surgery, 5 underwent adjuvant chemotherapy and 15 radiation therapy. After a median follow-up of 6.4 years, the cumulative incidences at 5-years of any, local and distant recurrences were of 26% (95% Confidence Interval [CI], 4-34%), 16% (95%CI, 10-24%) and 10% (95%CI, 5-16%), respectively. Tumor size ≥5 cm was associated with higher distant recurrences (p=0.05). Among small tumors (<5 cm), distant recurrences were higher in those with heterologous differentiation and/or multifocal disease (p=0.06). Evolution from and/or previous history of fibroadenomas, benign or borderline phyllodes tumors of the breast were associated with lower distant recurrences (p=0.014). Type of breast surgery (mastectomy vs. lumpectomy/excision) was not found to be significantly associated with distant (p=0.32) or local (p=0.17) recurrence, even after controlling local recurrence incidence for negative pathologic prognostic factors (p=0.17). Table: 101PCharacteristicN=131Age at diagnosis, median (IQR)46 (40-55)At least one negative prognostic factor, n (%)81 (62%) Size ≥5 cm, n (%)56 (43%) Multifocal disease, n (%)14 (11%) Heterologous differentiation, n (%)26 (20%)Type of last breast surgery Excisional biopsy (no attempt at margins), n (%)12 (9%) Lumpectomy (wide local excision with attention to margins), n (%)44 (34%) Mastectomy, n (%)75 (57%)Adjuvant radiotherapy, n (%)15 (11%)Adjuvant chemotherapy, n (%)5 (4%)Evolution from/previous history of fibroadenoma, benign or borderline phyllodes53 (40%) Open table in a new tab The natural history of B-MPT can be burdened by local and distant recurrences. Pathologic prognostic factors (i.e., tumor size, heterologous differentiation, multifocal disease, previous history of fibroepithelial tumors) more than the type of wide breast surgery (mastectomy vs. lumpectomy) seem to represent the most significant prognostic factors for recurrences.