Accelerated partial breast radiation with MammoSite balloon brachytherapy appears to control the tumor bed more effectively than whole breast irradiation, investigators reported at the annual meeting of the American Society of Breast Surgeons.
Dr. Peter Beitsch and his colleagues compared data from the society’s MammoSite Registry with prior findings from studies of whole-breast irradiation (WBI). They said the proportion of recurrences occurring in the tumor bed was much smaller with accelerated partial breast radiation (APBI) – 28% vs. about 69% in the earlier WBI data.
Dr. Peter Beitsch
"While it made common sense to a lot of us that APBI should offer better rates of local control, compared to WBI, since the radiation therapy with APBI is delivered directly to the tumor site, this is the first study to have actually proven this hypothesis," Dr. Beitsch, director of the Dallas Breast Center, said in an interview.
"WBI has been held as the ‘gold standard’ for post-lumpectomy radiation therapy, and our data may change that line of thought," he added.
Randomized trials demonstrate that lumpectomy with WBI yields survival rates equivalent to those seen with mastectomy; they also show that WBI has no impact on the ipsilateral occurrence of new "elsewhere" cancers in quadrants away from the primary tumor quadrant. Dr. Beitsch explained during a press briefing.
In all such trials, thus far, tumor bed recurrence rates have been higher than were the rates of ipsilateral "elsewhere" cancers, he said.
Now, however, 5-year actuarial data from 1,449 cases in 1,440 patients in the MammoSite registry show the opposite. The patients were treated at 97 institutions between May 2002 and July 2004. Most patients, 87%, were diagnosed with invasive breast cancer and the rest, 13%, with ductal carcinoma in situ (DCIS). Median follow up was 60 months.
Dr. Beitsch reported there have been 50 (3.5%) ipsilateral breast tumor recurrences: 14 (1.0%) at the initial tumor site and 36 (2.5%) elsewhere in the breast. The total actuarial rate of ipsilateral breast tumor recurrence was 3.61% (3.65 % for invasive disease and 3.36 % for DCIS). Tumor bed recurrences accounted for 28% of all recurrences, whereas recurrences elsewhere added up to 72%.
In contrast, historical data on whole-breast irradiation (WBI) from six studies demonstrate that tumor bed recurrences are about twice as common as recurrences elsewhere, approximately 69% vs. about 31% elsewhere, said Dr. Beitsch, co-principal investigator for the registry and lead author on the study.
The new findings contrast with a controversial retrospective study of breast brachytherapy in nearly 93,000 older women with invasive breast cancer. In that study, the mastectomy rate 5 years later was about twice as high in women treated with brachytherapy – cumulative incidence 3.95% vs. 2.18% with WBI. The difference persisted after a multivariate adjustment, with a hazard ratio of 2.19, according to a report published May 1, 2012, in JAMA.
Moreover, short-term and long-term complications, including breast pain, were significantly more common in women who had radiation delivered by brachytherapy. Overall survival was not significantly different, however, at about 87% in both groups studied, Dr. Dr. Grace L. Smith of the University of Texas M.D. Anderson Cancer Center in Houston and her coauthors reported (JAMA 2012;307:1827-37).
In a press release asserting that the new study contradicts the JAMA report, Dr. Beitsch called attention to limitations of the M.D. Anderson study: He noted that it is based on Medicare claims data, which often do not provide an accurate clinical picture. In addition, many of the end points are "soft," poorly defined and difficult to quantify, he said, adding that the reported complication rates after breast surgery and radiotherapy vary widely, and are subject to under- or over-reporting.
Finally, "the authors’ inferences of harm to patients from breast brachytherapy are speculative," he said.
Dr. Hiram S. Cody III
The American Society of Breast Surgeons (ASBrS) is one of three groups that previously issued rebuttals to the retrospective study. In the same press release, ASBrS executive committee member Dr. Hiram S. Cody III said that ASBrS continues to support its Consensus Statement on APBI and guidelines for patient selection, which was revised Aug. 15, 2011.
"APBI appears to be safe and effective treatment for properly selected breast conservation patients," said Dr. Cody, an attending surgeon at Memorial Sloan-Kettering Cancer Center and professor of clinical surgery at Cornell University, both in New York.
"We wish to emphasize that, although the 6-year results of APBI are encouraging, they do not conclusively establish equivalence with WBI, for which the supporting data include multiple randomized trials with follow-up exceeding 20 years, and meta-analyses that conclusively link local control and survival," Dr. Cody stated.