A recent study published in Nature demonstrates the efficacy and safety of hypofractionated partial breast irradiation (PBI) in patients with early-stage breast cancer. The trial, involving 208 patients, assessed cosmetic outcomes, normal tissue effects, and disease control following breast-conserving surgery and PBI.
The study enrolled female patients aged 50 years or older with newly diagnosed, unilateral, unifocal, non-lobular invasive breast cancer (pT1, ≤ 20 mm), estrogen receptor-positive tumors, clear surgical margins (≥ 2 mm), and node-negative status (pN0). Patients received 40.05 Gy to the planning target volume (PTV) in 15 fractions over three weeks, using intensity-modulated radiation therapy (IMRT).
Cosmetic Outcomes
Physician-assessed cosmetic outcomes were favorable. At baseline, 89.4% of patients had excellent or good cosmesis. The 3-year overall cosmetic deterioration rate was only 3.5%. This suggests that the IMRT-based hypofractionated regimen is cosmetically acceptable for selected patients.
Normal Tissue Effects
Acute and late normal tissue effects were minimal. Grade 2 radiation dermatitis was reported in 5.8% of patients within one month of PBI completion, with no grade 3 or 4 events. At 3 years post-PBI, grade 2 breast induration was observed in 1.5% of patients. Lymphedema was rare, with stage 1 observed in only 0.5% of patients.
Disease Control and Survival
At a median follow-up of 66.3 months, the cumulative incidence of ipsilateral breast tumor recurrence (IBTR) and regional recurrence (RR) at 5 years was 0.5% each. The 5-year disease-free survival (DFS) was 99.0% (95% CI: 97.5-99.7%). The 5-year overall survival (OS) was 97.9% (95% CI: 96.5-99.4%).
Comparison with Other Trials
The study's findings align with other trials that have demonstrated the noninferiority of PBI versus whole breast irradiation (WBI) in preventing local recurrence, particularly in women with small, low-grade, ER-positive, and node-negative tumors. The low IBTR rate in this trial supports the oncological safety of the IMRT-based moderately hypofractionated regimen for selected patients.
The trial's results also compare favorably with other PBI trials using IMRT techniques, which have shown better toxicity profiles and cosmesis compared to 3D-CRT techniques. The use of IMRT is thought to improve dose homogeneity, contributing to the favorable outcomes observed in this study.
Limitations
The authors acknowledge limitations, including the relatively small sample size and shorter follow-up period. The 3-week duration of the PBI regimen is also longer compared to some other PBI schedules. Future research will focus on whether a shorter course of PBI maintains comparable toxicity profile and cosmetic outcome.
Clinical Implications
The study supports the use of a moderately hypofractionated PBI regimen of 40.05 Gy in 15 fractions delivered by IMRT technique as a cosmetically acceptable and clinically safe option for treating patients with low-risk early breast cancer. This regimen is consistent with the latest ASTRO PBI guidelines.
