1942P Non-metastatic malignant phyllodes tumors of the breast (B-MPT): A retrospective analysis from a referral center

B-MPT accounts for <1% of breast neoplasms. The standard treatment for non-metastatic disease consists of wide local excision. Type of excision and adjuvant treatments are still matter of debate. Because of its rarity, only few case series with less than 100 B-MPT patients (pts) are available. We conducted a retrospective single-centre observational study to describe outcomes and possible prognostic factors of pts with B-MPT. Data of consecutive patients aged ³18 years old, with a histologically confirmed diagnosis of non-metastatic B-MPT, who underwent surgery from January 2000 to December 2021, were collected. The primary endpoint was recurrence-free survival (RFS). Survival was calculated using Kaplan–Meier method. Multivariable analysis was performed with Cox proportional hazards model (significance at p-value<0.05). 131 pts were included. Patient characteristics are reported in table. All patients received a surgery, 5 adjuvant anthracycline-based chemotherapy and 15 radiation therapy. After a median follow-up of 6.8 years, 36 (28%) pts experienced a disease recurrence: 19 (15%) a distant and 23 (18%) a loco-regional relapse. The median RFS, distant RFS (DRFS) and local RFS (LRFS) were not reached. The 5-year RFS, DRFS and LRFS rates were of 72%, 85% and 82%. At univariate analysis DRFS significantly correlated with the presence of at least one negative pathological prognostic factor (i.e., Size >5 cm, Multifocal disease or Heterologous differentiation [SMH]) (p=.03). If adjusted for type of breast surgery, SMH was associated also with LRFS (HR 3.3; 95%CI, 1.4-7.8; p=.008). The type of surgery was not prognostic for RFS, DRFS and LRFS. Table: 1942PPatient characteristicsN=131Age at diagnosis, mean (DS)46.7 (12.7)Negative pathological prognostic factorsSize >5 cm - %43%Multifocal disease - %11%Heterologous differentiation - %20%At least one negative prognostic factor - %62%Surgery strategyUpfront wide local excision with attention to margins - %45%Re-excision after previous inadequate resection - %46%Inadequate resection without re-excision - %9%Type of last breast surgeryExcisional biopsy (no attempt at margins) - %9%Lumpectomy (wide local excision with attention to margins) - %34%Mastectomy - %57%pR1 - %14%Adjuvant chemotherapy - %4%Adjuvant radiotherapy - %11% Open table in a new tab Natural history of B-MPT is burdened by local and distant recurrences. Pathological features more than the type of wide local excision seem to represent the most significant prognostic factor for recurrences.