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Original Investigation
August 2017

Association of Radiotherapy Boost for Ductal Carcinoma In Situ With Local Control After Whole-Breast Radiotherapy

Author Affiliations
  • 1Smilow Cancer Center, Department of Therapeutic Radiology, Yale School of Medicine, New Haven, Connecticut
  • 2Department of Biostatistics, Yale School of Public Health, New Haven, Connecticut
  • 3Department of Radiation Therapy, Institut Curie, Paris, France
  • 4Department of Radiation Therapy, Oakland University William Beaumont School of Medicine, Royal Oak, Michigan
  • 5Department of Radiation Oncology, University of Texas MD Anderson Cancer Center, Houston
  • 6Department of Radiation Oncology, Harvard Medical School, Dana Farber Cancer Institute, Boston, Massachusetts
  • 7Department of Radiation Oncology, University of Pennsylvania, Philadelphia
  • 8Department of Radiation Oncology, University of Montreal, Hôpital Maisonneuve-Rosemont, Montreal, Quebec, Canada
  • 9Department of Radiation Oncology, McGill University Health Centre, Montreal, Quebec, Canada
  • 10Department of Radiation Therapy, Robert Wood Johnson Medical School, New Brunswick, New Jersey
  • 11Department of Radiation Oncology, British Columbia Cancer Agency, Victoria, British Columbia, Canada
JAMA Oncol. 2017;3(8):1060-1068. doi:10.1001/jamaoncol.2016.6948
Key Points

Question  Is the use of a radiotherapy boost to the tumor bed associated with improved local control in women with ductal carcinoma in situ treated with breast-conserving surgery and whole-breast radiotherapy?

Findings  In this analysis of 4131 patients, an a priori power analysis was used to estimate the sample size required to detect an outcome benefit of radiotherapy boost, and a pooled evaluation showed that a radiotherapy boost was associated with reduced in-breast tumor recurrence at 10 and 15 years. On multivariable analysis, the boost remained significantly associated with reduced in-breast tumor recurrence independent of age and tamoxifen citrate use.

Meaning  For patients with ductal carcinoma in situ and life expectancy of more than 10 to 15 years, the addition of a radiation boost dose may be considered to provide an incremental benefit in improving local control after whole-breast radiotherapy.

Abstract

Importance  The use of a radiotherapy (RT) boost to the tumor bed after whole-breast RT (WBRT) for ductal carcinoma in situ (DCIS) is largely extrapolated from invasive cancer data, but robust evidence specific to DCIS is lacking.

Objective  To compare ipsilateral breast tumor recurrence (IBTR) in women with DCIS treated with vs without the RT boost after breast-conserving surgery and WBRT.

Design, Setting, and Participants  This retrospective analysis pooled deidentified patient-level data from 10 academic institutions in the United States, Canada, and France from January 1, 1980, through December 31, 2010. All patients had newly diagnosed pure DCIS (no microinvasion), underwent breast-conserving surgery, and received WBRT with or without the boost with a minimum of 5 years of follow-up required for inclusion in the analysis. Given the limited events after WBRT, an a priori power analysis was conducted to estimate the DCIS sample size needed to detect the anticipated benefit of the boost. Data were uniformly recoded at the host institution and underwent primary and secondary reviews before analysis. Sample size calculations (ratio of patients who received the boost dose to those who did not, 2:1; α = .05; power = 80%) estimated that 2982 cases were needed to detect a difference of at least 3%. The final analysis included 4131 patients (2661 in the boost group and 1470 in the no-boost group) with a median follow-up of 9 years and media boost dose of 14 Gy. Data were collected from July 2011 through February 2014 and analyzed from March 2014 through August 2015.

Interventions  Radiotherapy boost vs no boost.

Main Outcomes and Measures  Ipsilateral breast tumor recurrence.

Results  The analysis included 4131 patients (median [SD] age, 56.1 [10.9] years; range, 24-88 years). Patients with positive margins, unknown estrogen receptor status, and comedo necrosis were more likely to have received an RT boost. For the entire cohort, the boost was significantly associated with lower IBTR (hazard ratio [HR], 0.73; 95% CI, 0.57-0.94; P = .01) and with IBTR-free survival (boost vs no-boost groups) of 97.1% (95% CI, 0.96-0.98) vs 96.3% (95% CI, 0.95-0.97) at 5 years, 94.1% (95% CI, 0.93-0.95) vs 92.5% (95% CI, 0.91-0.94) at 10 years, and 91.6% (95% CI, 0.90-0.93) vs 88.0% (95% CI, 0.85-0.91) at 15 years. On multivariable analysis accounting for confounding factors, the boost remained significantly associated with reduced IBTR (HR compared with no boost, 0.68; 95% CI, 0.50-0.91; P = .01) independent of age and tamoxifen citrate use.

Conclusions and Relevance  This patient-level analysis suggests that the RT boost confers a statistically significant benefit in decreasing IBTR across all DCIS age groups, similar to that seen in patients with invasive breast cancer. These findings suggest that a DCIS RT boost to the tumor bed could be considered to provide an added incremental benefit in decreasing IBTR after a shared discussion between the patient and her radiation oncologist.

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