In a Canadian phase II trial (OPAR) published in the Journal of Clinical Oncology, researchers assessed the cosmetic outcomes of two partial breast irradiation (PBI) schedules in patients with early breast cancer. The study, led by Timothy J. Whelan, BM, BCh, aimed to determine if PBI schedules of five daily fractions of 30 Gy or 27.5 Gy over 1 week resulted in acceptable adverse cosmesis for evaluation in a phase III trial. The results indicated that both schedules met acceptability criteria at 2 years based on photographic assessment.
The multicenter trial randomized 281 patients to receive either 30 Gy (n = 142) or 27.5 Gy (n = 139). Eligible patients were aged 50 years or older (median age 65 years) and had invasive breast cancer or ductal carcinoma in situ ≤ 3 cm treated by lumpectomy, with negative axillary nodes. The primary outcome was adverse cosmesis, defined as fair or poor by photographic assessment at 2 years. The tolerance margin was set at 23%, based on a 17% risk of adverse cosmesis observed with whole-breast irradiation.
Key Findings on Cosmetic Outcomes
At 2 years, adverse cosmesis rates were 12.1% (90% CI = 8.2%–17.6%) in the 30-Gy group and 15.2% (90% CI = 10.8%–21.1%) in the 27.5-Gy group, meeting acceptability criteria on photographic assessment. Nurse assessments at 2 years also showed acceptable cosmesis rates of 12.9% (90% CI = 8.8%–18.4%) in the 30-Gy group and 7.7% (90% CI = 4.7%–12.5%) in the 27.5-Gy group.
However, patient self-assessment at 3 years revealed an adverse cosmesis rate of 20.1% (90% CI = 13.6%–30.0%) in the 30-Gy group, which did not meet acceptability criteria, compared to 13.0% (90% CI = 7.6%–21.4%) in the 27.5-Gy group. Furthermore, at 5 years, grade ≥ 2 late toxicity was observed in 11.3% of the 30-Gy group and 5.8% of the 27.5-Gy group.
Implications for Future Trials
The investigators concluded that both 30 Gy and 27.5 Gy resulted in acceptable cosmetic outcomes according to the study design. However, in light of recent studies, a lower dose was chosen for the phase III trial. These findings suggest that while both schedules initially demonstrate acceptable cosmetic results, the lower dose of 27.5 Gy may offer improved long-term cosmetic outcomes and reduced late toxicity, warranting further investigation in larger trials.
