An accelerated 1-week regimen of partial-breast irradiation after breast-conserving surgery looks to be as effective as whole-breast irradiation, according to results from a retrospective analysis of more than 1000 women, published online April 28 in the Annals of Surgical Oncology.
Women treated with a 1-week course of adjuvant accelerated partial-breast irradiation (APBI) after lumpectomy had long-term outcomes similar to what would be expected with the standard 5- to 7-week course of whole-breast irradiation, according to Mitchell Kamrava, MD, from the Department of Radiation Oncology at the University of California, Los Angeles, and his colleagues from the Pooled Registry of Multicatheter Interstitial Sites (PROMIS) group.
However, results from ongoing randomized North American and European trials directly comparing ABPI with whole-breast irradiation will have to be reported before final conclusions can be drawn.
This retrospective study is "the largest report of outcomes with interstitial breast brachytherapy," note the authors. "This treatment resulted in excellent long-term local control and cosmesis outcomes," they write.
At a mean of 6.9 years after APBI, the 10-year actuarial risk for an ipsilateral breast tumor recurrence was 7.6%, risk for regional failure was 2.3%, risk for distant metastasis was 3.8%, cause-specific survival was 96.3%, overall survival was 86.5%, and risk for new contralateral cancers was 4.6%. For patients with at least 5 years of follow-up, physician-reported cosmesis was excellent/good in 84%.The only variables associated with increased risk for local recurrence on multivariate analysis were high-grade tumors and positive margins.
"One of the rationales for pursuing partial-breast radiation was the possibility that patients would have equal outcomes to treating the whole breast, since the majority of the time local recurrences happen near the lumpectomy cavity. These data suggest that this hypothesis may be true for the group of women who are candidates for partial-breast radiation," Dr Kamrava told Medscape Medical News.
The PROMIS registry involved 1356 patients treated from 1992 to 2013 with breast-conserving surgery and APBI using interstitial multicatheter brachytherapy. Data covering at least 1 year of oncologic and cosmesis outcomes were available for 1131 patients.
In the study cohort, median age was 59 years, 73% of the patients had invasive ductal carcinoma, 18% had ductal carcinoma in situ (DCIS), 83% had estrogen receptor (ER)-positive disease, 70% had progesterone-receptor-positive disease, and 6% were positive for human epidermal growth-factor receptor 2. For tumor stages, 18% were Tis, 75% were T1, and 8% were CT2; for nodal status, 73% were N0 AND 6% were N1a.
Coauthor Robert R. Kuske, MD, from Arizona Breast Cancer Specialists in Scottsdale, told Medscape Medical News that "the key selection criteria for APBI used by the physicians in this registry trial were invasive carcinomas or DCIS that have a pathologic size of 3 cm or less, lumpectomy with clear margins (i.e., no ink on tumor), and negative axillary nodes or minimal involvement of one to three nodes without extracapsular extension."
Dr Kuske added that "it is important for all oncologists to note that these were not the most favorable breast cancers in most other studies. We included women under the age of 50 years, grade 3 tumors, triple-negative, HER2 overexpressed, node-positive, extensive intraductal component, pure DCIS, lobular cancers, close margins, and lymph-vascular invasion."
Whole-Breast Irradiation Regimens Have Changed
Approached for comment, Thomas A. Buchholz, MD, professor, executive vice president, and physician-in-chief at the University of Texas M.D. Anderson Cancer Center in Houston, agreed that the PROMIS data are encouraging but noted that whole-breast irradiation regimens are also becoming briefer.
"I would consider this to be an important contributor to the outcome data concerning one method of performing APBI (interstitial multicatheter)," he said, but added that "during the same past decade, the conventional whole-breast approach has changed, too, making it much more convenient for patients, and less costly. Specifically, well-conducted trials in Canada and the United Kingdom confirmed that you don't need to treat with 30 treatments of whole breast, but can safely do it in 15 or 20. Accordingly, the patient convenience benefits of APBI vs whole breast become much more similar."
Dr Buchholz noted that the outcomes are reasonable and give confidence in APBI via multicatheter interstitial brachytherapy, but he also pointed out that the study population had favorable disease (most older than 50 years, most having ER-positive disease, most having T1 stage disease, most having LN-negative disease). "In this setting, whole-breast radiation with modern surgery and systemic therapies yields local and regional recurrence rates of about 0.5% per year, so it isn't clear whether this approach is truly equivalent. It could be interpreted as being twice as high a risk by some, and others would interpret it as being in the same ball park," he said.
In addition to efficacy, researchers working on strategies for partial-breast irradiation hoped to achieve greater safety and better patient adherence. The key safety issue is that whole-breast radiotherapy exposes both the heart and the lung to radiation. The compliance problem is that the typical 5- to 7- week course of whole-breast radiation is difficult for some patients to sustain, often because of logistics.
Dr Kamrava said that the PROMIS data support the conclusion that APBI is a reasonable option for many patients, a recommendation that is consistent with existing guidelines from the American Society for Radiation Oncology (ASTRO), the American Brachytherapy Society, the Groupe Européen de Curiethérapie–European Society for Radiotherapy and Oncology, and the American Society of Breast Surgeons.
Dr Kuske said that "multicatheter breast brachytherapy is an option for breast-conserving therapy for women meeting our selection criteria. A 4- or 5-day alternative to 6 and a half weeks of whole-breast radiation therapy, or 3 weeks of whole-breast radiation therapy, is attractive to many women with early-stage breast cancer because it is less disruptive to their lifestyle, work, and family, and minimizes radiation exposure to the heart (left breast cancers) and lung." However, he stressed that these results should not be extrapolated to intraoperative radiotherapy.
Dr Kuske added that "interstitial brachytherapy would likely be the least common approach to APBI. This study gives some credence to the notion that if you use this approach, it can yield acceptable outcomes, but I don't think it necessarily changes how I think about APBI use."
According to Dr Kuske, results from the ongoing European randomized trial are expected in late 2015. "If the two treatments are equal, or superior for APBI, many if not most patients will be choosing the -4 or 5-day option. Who is going to teach the thousands of North American oncologists how to perform multicatheter interstitial brachytherapy?" he asked.
Dr Buchholz said that his approach for such patients is to treat them for 3 weeks of whole-breast treatment, which is noninvasive and only adds another week, compared with the planning and treatments often used in APBI.
Clinical practice guidelines for the use of partial-breast irradiation are currently under review. Dr Kamrava noted that "we were encouraged that even though there were many patients in this registry that fall within either the 'cautionary' or 'unsuitable' groups, as per the ASTRO partial-breast consensus guidelines, we did not see higher local failure rates. We believe that our encouraging data should be considered when the guidelines are updated."
The study was supported by an unrestricted educational grant from Elekta. The authors and Dr Buchholz have disclosed no relevant financial relationships.
J Ann Surg Oncol. Published online April 28, 2015. Abstract
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Cite this: Excellent Outcomes With Partial-Breast Irradiation - Medscape - Jul 01, 2015.
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