Tumor bed boost added to whole-breast irradiation reduces local recurrence rates in DCIS
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The addition of tumor bed boost following conventional or hypofractionated whole-breast irradiation reduced the rate of local recurrence among women with non-low risk ductal carcinoma in situ, according to randomized phase 3 study results.
The results, presented at the virtual San Antonio Breast Cancer Symposium, also showed no difference in recurrence rates between conventional and hypofractionated whole-breast irradiation (WBI).
“WBI after conservative surgery for DCIS reduces risk for local recurrence,” Boon H. Chua MBBS, PhD, FRANZCR, professor of medicine at University of New South Wales and director of cancer and hematology services at Nelune Comprehensive Cancer Centre of Prince of Wales Hospital, said during her presentation. “However, there has been no high-level evidence on the optimal radiation dose fractionation for DCIS to inform practice and improve patient outcomes.”
Chua and colleagues evaluated the role of dose escalation to the tumor bed and fractionation sensitivity of WBI by measuring the time to local recurrence among 1,608 women with non-low risk DCIS who underwent conservative surgery with at least 1 mm margins.
Researchers defined non-low risk DCIS as occurring among women aged younger than 50 years, or among women aged 50 years or older who had at least one additional risk factor, such as symptomatic presentation, palpable tumor, intermediate or high nuclear grade or central necrosis.
The analysis included two comparisons. Researchers assessed WBI alone or with sequential tumor bed boost consisting of 16 Gy in eight daily fractions, and they compared conventionally fractionated WBI, consisting of 50 Gy in 25 daily fractions, with hypofractionated WBI, consisting of 42.5 Gy in 16 daily fractions.
Time to local recurrence served as the study’s primary endpoint.
The trial included three randomization categories. Randomization A (n = 503) included four arms: conventionally fractionated WBI with or without tumor bed boost and hypofractionated WBI with or without tumor bed boost. Randomization B (n = 581) consisted of two arms: conventionally fractionated WBI with or without tumor bed boost. Randomization C (n = 524) also consisted of two arms: hypofractionated WBI with or without tumor bed boost.
In total, 803 women received tumor bed boost across these arms and 805 women did not receive boost, 831 women underwent conventional WBI (n = 415 with boost) and 777 women underwent hypofractionated WBI (n = 388 with boost).
The proportion of women who underwent planned endocrine therapy was similar in the boost and no-boost groups (13% for both).
Median follow-up was 6.6 years.
Results showed significantly more women assigned tumor bed boost than no boost achieved 5-year freedom from local recurrence (97% vs. 93%; HR = 0.47; 95% CI, 0.31-0.72). This effect did not appear to significantly differ based on age, tumor size, nuclear grade, surgical margin or receipt of endocrine therapy.
Local recurrences were invasive in 44% of the no-boost group and 45% of the boost group.
The boost group also showed higher rates of freedom from disease recurrence (97% vs. 91%; HR = 0.63; 95% CI, 0.46-0.87), which also did not differ by WBI fractionation.
Researchers observed no difference in local recurrence rates between hypofractionated and conventional WBI among women in randomization A (94% for both groups; HR = 0.94; 95% CI, 0.51-1.73) and all women (95% for both groups; HR = 0.94; 95% CI, 0.51-1.74).
There also were no significant interactions between tumor bed boost and WBI fractionation on local recurrence for randomization A (HR = 1.09; 95% CI, 0.32-3.76) and among all women (HR = 0.94; 95% CI, 0.41-2.18).
Overall, grade 3 or grade 4 toxicity was uncommon, Chua said.
More women who underwent tumor bed boost experienced grade 2 or higher late breast pain (n = 116 vs. 77; P = .003) and induration or fibrosis (n = 110 vs. 49; P < .0001).
“Long-term follow-up is required to confirm these findings,” Chua said. “The significance of the study is strengthened by published longitudinal patient-reported outcomes and cosmetic evaluation data, and the tissue resource for biomarker research on invasive recurrence of DCIS.”
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Chua BH, et al. Abstract GS2-04. Presented at: San Antonio Breast Cancer Symposium (virtual meeting); Dec. 8-11, 2020.
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