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Radiation boost after whole breast radiation therapy for DCIS reduces local tumor recurrence
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A radiation boost improved local control and reduced local tumor recurrence among patients with ductal carcinoma in situ who underwent whole breast radiation therapy after lumpectomy, according to study results presented at the ASTRO Annual Meeting.
“This data supports the use of a boost for patients with ductal carcinoma in situ (DCIS) who have life expectancies of 10 or more years, and who are planning to get radiation therapy as part of their treatment plan,” Meena Savur Moran, MD, professor of therapeutic radiology at Yale School of Medicine and director of the radiation oncology breast program at Smilow Cancer Hospital at Yale-New Haven, said during a press conference.
Breast conservation therapy — which consists of local excision of the primary tumor, followed by whole breast radiation therapy — is an alternative to mastectomy and is a standard treatment option for early-stage breast cancers.
After whole breast radiation therapy, many patients receive a radiation boost to the local tumor bed that allows for the delivery of four to eight more fractions to dose-escalate that region, which is at the greatest risk for local recurrence.
Prior research has shown radiation boosts provide a small but statistically significant reduction — about 4% at 20 years — in ipsilateral breast tumor recurrence among patients with invasive cancers.
Researchers have struggled to confirm the benefit of this approach due to the long natural history of DCIS and the limited number of ipsilateral breast tumor recurrence events after whole breast radiation therapy. Even though boosts are frequently administered in this setting, that is based on extrapolation of data obtained from patients with invasive cancers.
Moran and colleagues conducted their study to create a DCIS database to compare outcomes of patients who underwent whole breast radiation therapy with or without radiation boosts.
They conducted an a priori power calculation that determined 2,929 patients would be needed to demonstrate at least a 3% difference in recurrence rates between groups.
The final analysis — which pooled data from 10 academic centers in the United States, Canada and France — included 4,131 patients (median age, 56.1 years) with newly diagnosed DCIS without micro-invasion. Of this group, 2,661 patients received a radiation boost and 1,470 did not.
The median boost dose was 14 Gy and 4% of patients had positive margins.
Median follow-up was 9 years.
Patients who received radiation boosts were more likely to be free of ipsilateral breast tumor recurrence at 5 years (97.1% vs. 96.3%), 10 years (94.1% vs. 92.5%) and 15 years (91.6% vs. 88%; P = .0389).
When researchers accounted for factors that determine which patients receive a radiation boost — such as age, grade, necrosis, margin status and tamoxifen receipt — the boost remained an independent predictor of decreased local relapse.
Radiation boost also was significantly associated with reduced local relapse in patients with negative margins, regardless of whether margin status was defined by no ink on tumor or under the joint ASTRO, ASCO and Society of Surgical Oncology guideline of 2 mm or less (P < .001 for both).
An analysis of patients with negative margins stratified by age showed radiation boosts were significantly associated with reduced local relapse among those aged younger than 50 years (P = .0166) and those aged 50 years or older (P = .0073).
“This series represents the largest cohort to address the benefit of a radiation boost in DCIS,” Moran said. “Our findings do suggest that a boost results in a small but statistically significant benefit in decreasing local relapse across all age groups, similar in magnitude to what we see in invasive cancers.”
Moran acknowledged that a 4% reduction at 20 years may not seem like a lot.
“[However], it is clinically important for patients because we have learned from the invasive cancer data that this small incremental decrease has resulted in about a 40% [reduction in the] rate for salvage mastectomies for recurrences,” Moran said. – by Mark Leiser
Reference:
Moran MS, et al. Abstract 324. Presented at: ASTRO Annual Meeting; Sept. 25-28, 2016; Boston.
Disclosure: The researchers report no relevant financial disclosures.