ATLANTA — When partial-breast irradiation was delivered with the MammoSite balloon catheter system after lumpectomy, the majority of patients showed good to excellent cosmetic results and had no local recurrences of cancer at 2 years, according to the first analysis of MammoSite Registry Trial data, presented at a symposium that was sponsored by the Society of Surgical Oncology.
Partial-breast irradiation (PBI) offers women the convenience of shortening their course of radiation treatment from 6 weeks for standard whole-breast radiation to a week. It also has the potential to substantially improve the documented underutilization of breast-conserving therapy in the United States, Peter D. Beitsch, M.D., told this newspaper.
The trial enrolled 1,419 women to receive PBI instead of a mastectomy.
The best cosmetic results were seen in women with larger breasts or with at least 7 mm of breast tissue between the skin and the balloon catheter, which is inflated inside the lumpectomy cavity. The average skin spacing was 10 mm.
Less than 10% of the women who enrolled (139) could not be treated because of a lack of skin spacing, balloon failure, lack of cavity conformity, or positive nodes. PBI is contraindicated in patients who are very young or who are node positive.
Of the 1,280 women treated, only 1% had positive margins and 91% had tumor margins greater than 2 mm. About 80% of the women had T1 tumors, 6.3% had T2 tumors, and 13.3% had ductal carcinoma in situ.
Only 3% of the patients had positive lymph nodes. Two percent of patients had breast size A, compared with 20% B, 33% C, 23% D, and 22% not reported.
About 98% of the women received a radiation dose of 34 Gy in 10 fractions over 5 days, Dr. Beitsch said during the meeting.
Analysis of the results showed that good to excellent cosmesis was achieved in 1,030 (95%) of 1,084 women overall, 229 (92%) of 248 patients at 1 year, and 18 (94.7%) of 19 patients at 2 years. Fair to poor cosmesis was reported in 54 (5%) women overall, 19 (7.7%) of 248 patients at 1 year, and 1 (5.3%) of 19 patients at 2 years.
Good to excellent cosmetic results were reported in 89% of women when the skin spacing was 7 mm or more.
Surgeons can improve skin spacing by proper preoperative planning to determine who is a candidate for the therapy prior to surgery and performing the lumpectomy accordingly, Dr. Beitsch said during an interview with this newspaper.
“The surgeon [also] must make sure the margins of the lumpectomy are free of tumor, since partial breast radiation does not make up for inferior surgery,” added Dr. Beitsch, who is the director of the Dallas Surgical Group.
Data available on 1,140 women showed that there were 92 infections (8%), of which 60 were device related.
A total of 28% of patients reported radiation dermatitis, 20% had subcutaneous tissue changes, and 9% had late radiation skin changes.
The question of long-term radiation-related complications remains to be addressed, Dr. Beitsch said, adding that the 5-day radiation treatment is radiobiologically equivalent to about 54 Gy of whole-breast radiation.
There were no local recurrences, and one death was unrelated to treatment, Dr. Beitsch said.
No women in the study had augmented breasts. Dr. Beitsch suggested such patients would be better candidates for PBI with multiple catheters due to the inability to obtain enough skin spacing.
The MammoSite balloon catheter-based brachytherapy system is designed for inflation inside the lumpectomy cavity. Proxima Therapeutics, Inc.