Session Item

To confirm the results of the FAST-forward trial (Murray Brunt, 2020) in the clinical practice, a multicenter, retrospective and prospective observational study (NCT05586256) was designed. Data of BC pts treated with BCS and ultra-hypofractionated WBI were collected.

Inclusion criteria: early stage BC, age ≥ 18 years, BCS. Exclusion criteria: regional nodal RT, distant metastasis, history of previous malignancy. Treatment: WBI (26 Gy in 5 fr); Boost: sequential (7.6 Gy in 2 fr) or simultaneous integrated (30 Gy in 5 fr), according to clinical and pathological risk factors. Primary outcome: acute and chronic toxicity evaluation. Secondary outcomes: OS, DFS, rate of LR, regional relapse and distant metastasis, cosmetic outcome and QoL assessment. Toxicity evaluation: CTCAE v5.0 scale; Cosmetic outcome: Harvard Breast Cosmesis Grading Scale and photographic documentation (consensus scoring method, Haviland 2008); QoL assessment: EORTC QLQ-C3 and -BR23 questionnaries. Statistical analysis: bi- and multi-variate analyses.

From March 2020 to October 2022, 294 pts were enrolled from 5 Italian centers (Table 1). Median follow up was 10 months (range 1-28). Acute toxicity was recorded in 197/294 (67.0%) pts (cutaneous in 185 pts), 293 events were observed (76 pts developed more than 1 toxicity). Only 1 G3 event was recorded (0.3%) (Table 2). Late toxicity was recorded in 37.3% (76/204), 29.7% (35/118), 14.5% (9/62) and 12.5% (4/32) pts at 6, 12, 18 and 24 months respectively (Table 2). Toxicity was related with pts’ age, tumor’s characteristics (TNM, grading, bio-pathological profile), systemic therapies, RT treatment and dosimetric data. At bivariate analysis younger pts had more acute toxicity (p<0.001) and pts with larger breast PTV had more toxicity at 6 months (p=0.027). Among pts who developed acute toxicity, a higher frequency of hypertension (p=0.042) and smoking habits (p=0.043) was found, while those who did not develop acute toxicity more frequently were treated with AIs vs other ET regimens (p=0.025). Finally, pts who developed toxicity at 6 months, more frequently underwent ALND (p=0.013). At multivariate analysis only breast PTV (OR 1.14; CI95% 1.04-1.26) and smoking habits (OR 2.63; CI95% 1.12-6.17) were significantly correlated with 6 months toxicity. In our series LRs, regional relapses or distant metastasis were not recorded. Only 1 woman developed a second BC (in the irradiated breast, 17 months after WBI). One death not related to BC was recorded.

Our data confirmed that the FAST-forward schedule is safe in terms of acute toxicity, having recorded predominantly G1 toxicity, but longer follow up is needed to confirm late toxicity results. Since other 30 centers will participate in the study, we expect to recruit a significant number of pts and gather a lot of data in a relative short space of time. Our results lead us to increase the use of ultra-hypofractionated WBI.