A long-term retrospective study of breast cancer patients receiving accelerated partial breast irradiation (APBI) via interstitial brachytherapy suggests that women younger than 50 and those with positive lymph nodes could be suitable to receive the treatment.San Francisco United States — Wednesday, September 17, 2014
Current American Society for Radiation Oncology (ASTRO) guidelines place these patients in the “unsuitable” category for APBI. In presenting an abstract at the 2014 ASTRO meeting, Beaumont Health System’s Peter Y. Chen, MD, FACR, indicated that data from the PROMIS (Pooled Registry of Multi-catheter Interstitial Sites) study shows low local recurrence rates for women in the “unsuitable” group who received interstitial brachytherapy APBI. The presentation was selected as a “Best of ASTRO” abstract.
“In the absence of results from randomized studies on efficacy and outcomes for APBI, current ASTRO guidelines classify patients less than 50-years-old and those with positive lymph nodes as unsuitable”, said Dr. Chen, Professor, Oakland University, William Beaumont Hospital School of Medicine (Royal Oak, Michigan). “However, in terms of disease control, local recurrence rate was 7 percent at 10 years post-therapy for these patients. The results suggest that a broader group of patients than currently described in the ASTRO guidelines are suitable.
The PROMIS registry study, supported by an unrestricted grant from Elekta, represents pooled data from five institutions* with extensive experience in the delivery of interstitial brachytherapy for APBI. The group collected data from 1992 to 2013 (1,374 patients), retrospectively evaluating long-term outcomes of patients treated with interstitial brachytherapy APBI. Dr. Chen’s ASTRO abstract presentation was the fourth for PROMIS in 2014.
APBI is a therapeutic approach that treats only the lumpectomy bed in addition to a 1-2 cm margin, rather than the whole breast. Because of the small volume of irradiation a higher dose can be delivered in a shorter time – twice a day over four or five days, versus external beam radiotherapy, which involves five treatments per week for four to six weeks. Interstitial brachytherapy involves the implantation of multiple thin catheters into the breast, surrounding the tumor site. A high-activity radioactive source is introduced by cables into the catheters. The source then travels sequentially through each cable until the prescribed dose is delivered.
“Among many oncologists worldwide there is a misconception about the ASTRO APBI guidelines. They think the ‘unsuitable’ group was categorized based on poor APBI outcomes,” says Robert Kuske, MD, PROMIS principle investigator and Medical Director of Arizona Breast Cancer Specialists, a division of Arizona Center for Cancer Care. “But, in reality, the criteria were established with data available in 2009. At that time, clinical trial data and long-term experience with clinicopathological features – outside of the traditionally favorable early stage breast cancer patients – were not well-known and established. In our study, women under 50 and those with positive lymph nodes appear to do quite well with APBI.”
Dr. Kuske sees a great deal of potential in the PROMIS study over the next few years.
“We have a lot of statistical power with this data set,” he says. “This is now one of the largest and most broad spectrum registries in the history of breast cancer, and with the addition of Southwest Radiation Oncology [Oklahoma City, Oklahoma], we will surpass the numbers of patients in the well-known MammoSite® registry trial. Such a large number of patients allows us to perform subset analyses, enabling us to provide data with better validity on specific aspects of breast cancer. For example, we plan to analyze outcomes of interstitial brachytherapy by genetic profiling, which will be presented at the American Society of Clinical Oncology breast cancer meeting in September.
“We’re going to do many different analyses,” Dr. Kuske adds. “We plan to continue mining this database so that the breast oncology community can benefit from the updated results of the PROMIS group’s efforts.”
*Arizona Breast Cancer Specialists, Gamma West Cancer Services, UCLA, University of Wisconsin, William Beaumont Hospital
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