BOSTON – Adding a boost dose after surgery and whole-breast radiation therapy (WBRT) for ductal carcinoma in situ offers a small but significant reduction in long-term risk of same-breast recurrence, according to results of a multicenter study.
An analysis of pooled data from 10 institutions showed that after 15 years of follow-up, 91.6% of women who had been treated with breast-conserving surgery, WBRT, and a boost dose remained free of ipsilateral breast tumor recurrence (IBTR), compared with 88% of women who received WBRT alone, reported Meena Savur Moran, MD, director of the breast cancer radiotherapy program at Smilow Cancer Hospital, Yale New Haven, Connecticut.
Dr. Meena Savur Moran
The absolute differences between the groups – 3% at 10 years, and 4% at 15 years – “don’t seem like a lot, but it is clinically important for patients, because what we’ve learned from the invasive cancer data is that this small, incremental decrease results in about a 40% less mastectomy rate for salvage mastectomies for recurrences,” she said.
It is common practice in many centers to give a radiation boost to the tumor bed of 8-16 Gy in 4-8 additional fractions following breast-conserving surgery and WBRT. This has been shown in invasive cancers to be associated with a statistically significant decrease in risk for IBTR in all age groups of about 4% at 20 years.
Yet because DCIS generally has an excellent prognosis with very few recurrences after whole-breast irradiation, it has been harder to determine whether radiation boosting would offer similar benefit to that seen in invasive cancers,
In an attempt to answer this question, investigators from 10 centers collaborated to create a DCIS database of patients treated with WBRT either with or without boost, and then analyzed the results.
The final cohort included 4,131 patients, far exceeding the minimum sample size the statisticians calculated would be needed to detect a benefit.
The median age of patients at the time of therapy was 56.1 years, median follow-up was 9 years, and the median boost dose was 14 Gy. In all, 4% of patients had positive tumor margins after surgery.
Rates of IBTR-free survival with boost vs. no boost were 97.1% vs. 96.3% at 5 years, 94.1% vs. 92.5% at 10 years, and, as noted before, 91.6% vs. 88% at 15 years (P = .0389).
In both univariate and in multivariate analysis controlling for tumor grade, comedo carcinoma, tamoxifen use, margin status, and age, IBTR was significantly associated with lower risk for recurrence.
The investigators also conducted a boost/no boost analysis stratified by margin status using both the National Surgical Adjuvant Breast and Bowel Project (NSABP) definition of negative margins as no ink on tumor, and the joint Society of Surgical Oncology, ASTRO, and American Society of Clinical Oncology guideline definition as less than 2 mm, and in each case found that among patients with negative margins, boosting offered a significant recurrence-free advantage.
Finally, they found that boosting offered a significant advantage both for patients 50 and older (P = .0073) and those 49 and younger (P = .0166).
“For DCIS, most of who treat breast cancer have used a boost, but we really extrapolated from the treatment from invasive breast cancer. Evidence for this practice until now in specific for DCIS has been lacking,” said Geraldine Jacobson, MD, MPH, professor and chair of radiation oncology at West Virginia University, Morgantown. Dr. Jacobson moderated the briefing.
She noted that the large sample size and long follow-up of the study was necessary for the treatment benefit to emerge.