A radiation boost to the local tumor bed following treatment with breast-conserving therapy (ie, local excision followed by whole-breast radiation therapy) improves local control for patients with ductal carcinoma in situ, according to a study of pooled data from 10 academic centers,1 presented at the 58th Annual Meeting of the American Society of Radiation Oncology (ASTRO). The magnitude of improvement is similar to that seen for a radiation boost in invasive breast cancer.
The benefit we saw in decreasing local relapse rates in this study was of similar magnitude as has been shown for invasive cancers: 4% at 20 years for invasive cancers and 3% at 15 years for [ductal carcinoma in situ]. While these small numbers may not seem substantial, this is clinically important for patients.— Meena S. Moran, MD
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“Previously, radiation oncologists extrapolated the boost data from invasive cancers to provide the rationale for using the radiation boost in ductal carcinoma in situ. The invasive boost cancer trials have demonstrated a small but significant benefit in decreasing local relapse in all age groups for invasive cancers. There is no reason to think that this benefit would not also exist for [ductal carcinoma in situ]. This study provides convincing evidence that a radiation boost achieves a level of risk reduction for patients with [ductal carcinoma in situ] similar to that seen for patients with invasive breast cancer,” explained lead author Meena S. Moran, MD, of Yale University School of Medicine, New Haven, Connecticut.
Study Design
It is difficult to conduct a randomized trial to demonstrate the effectiveness of a radiation boost in ductal carcinoma in situ, because the disease has an excellent prognosis with few ipsilateral breast tumor recurrences. Large numbers of patients and very long follow-up would be necessary to demonstrate the effectiveness of a radiation boost in this setting, she continued.
To examine this issue, the investigators pooled data from 10 different academic centers in North America and France to create a database on 4,131 deidentified patients with ductal carcinoma in situ treated with breast-conserving therapy with and without a radiation boost. To be eligible for inclusion, patients had to have newly diagnosed pure ductal carcinoma in situ with no microinvasion treated with breast-conserving surgery and whole-breast radiation therapy with or without a boost.
Of these patients, 2,661 had received a boost and 1,470 had not. Use of a boost was more common in those with positive margins following surgery, those with unknown estrogen receptor status, and those with the presence of necrosis in the pathology report.
“This is the largest database on patients with [ductal carcinoma in situ] treated with or without breast boost to date,” Dr. Moran said.
Key Findings
Median boost dose was 14 Gy, median age was 56.1 years, and positive margins were found in 4%. With a median follow-up of 9 years, a statistically significant difference favoring a boost was observed for decreasing the risk of ipsilateral breast tumor recurrence (P = .0389), with 5-year ipsilateral breast tumor recurrence–free survival of 97.1% for the boost group vs 96.3% for those who did not have a boost, 94.1% vs 92.5% at 10 years, and 91.6% vs 88% at 15 years, respectively.
A reduction in the risk of ipsilateral breast tumor recurrence was seen across all age groups. The boost was an independent predictor for decreased ipsilateral breast tumor recurrence risk in a multivariate analysis that accounted for patient and disease characteristics such as age, grade, necrosis, margin status, tumor size, and use of tamoxifen (P < .010).
Radiation Boost for Ductal Carcinoma in Situ
- Many centers use a radiation boost to the tumor bed for ductal carcinoma in situ treated with breast-conserving therapy; this practice has been based on a reduced risk of local recurrence observed in invasive cancers treated with a boost.
- A large study of pooled data from 10 academic centers now clearly demonstrates that a radiation boost to the tumor bed reduces the risk of ipsilateral breast tumor recurrence in patients with ductal carcinoma in situ by an estimated 3% over 15 years, similar to what is seen in invasive breast cancer (4% at 20 years).
- The invasive cancer data have demonstrated that these small benefits in decreasing local relapse translate to an approximately 40% reduction in the need for salvage mastectomy in patients.
- Radiation boost to the tumor bed should be considered for women with ductal carcinoma in situ treated with breast-conserving therapy who have life expectancies of more than 10 to 15 years who intend on receiving whole-breast radiation therapy.
When results were analyzed by margin status, the boost was significantly more effective in reducing the risk of ipsilateral breast tumor recurrence in those with negative margins, according to both the old definition of positive margins (“ink on margin”; P < .001) and the newer definition (< 2 mm; P < .001).
Dr. Moran noted that the subset of patients with positive margins (4% of the total population) was underpowered to show a statistically significant benefit for the boost in this subgroup. Receiving a radiation boost significantly decreased ipsilateral breast tumor recurrence in women aged 50 or older (P = .0073) and in younger women (P = .0166).
Clinical Implications
“The benefit we saw in decreasing local relapse rates in this study was of similar magnitude as has been shown for invasive cancers: 4% at 20 years for invasive cancers and 3% at 15 years for [ductal carcinoma in situ],” she told listeners at a press conference.
“While these small numbers may not seem substantial, this is clinically important for patients. The invasive boost data have shown us that these small incremental benefits of 3% to 4% [over time] with the use of a boost reduce the rate of salvage mastectomy for in-breast recurrence by approximately 40%. These data support use of a boost for women with [ductal carcinoma in situ] who have life expectancies of 10 to 15 years and who are receiving radiation therapy as part of their treatment plan,” Dr. Moran concluded. ■
Disclosure: Dr. Moran reported no potential conflicts of interest.
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