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A recent study has found that in breast cancer patients, the use of implantable accelerated partial breast irradiation therapy (IAPBI) after lumpectomy has increased dramatically since 2000. The increase was seen in women of all ages, but was statistically significant in those aged older than 40 years, and was most notable in those aged older than 80 years.

Andrea Abbott, MD, and colleagues from the surgical department at the University of Minnesota used the Surveillance, Epidemiology, and End Results (SEER) database to evaluate rates and trends of whole-breast radiation therapy (WBRT) and IAPBI from 2000 to 2007 (Cancer. Published online ahead of print February 1, 2011. doi: 10.1002/cncr.25927). The study cohort included women with a diagnosis of ductal carcinoma in situ (DCIS) or stage I or stage II breast cancer who had breast-conserving surgery (BCS) and radiation therapy (RT). The only categories of RT evaluated were external beam radiation and radioactive implants.

Investigators identified 127,257 patients meeting the inclusion criteria. Women in the IAPBI group were significantly more likely to be older, be widowed, and have stage I disease. Geographical differences were noted, with 0.5% of women treated with RT in Hawaii receiving IABPI and 7.2% of those in Atlanta receiving IAPBI.

The overall proportion of patients treated with IAPBI increased from 0.4% to 6.8%, with the proportion of those receiving WBRT declining from 99.6% to 93.2% over the study period. The most dramatic increase in the use of IAPBI was observed in patients aged older than 80 years, with an increase from 0.85% to 9.6%.

On logistic regression analysis including several patient and tumor variables, the time trends in IAPBI use remained significant, with an odds ratio of about 20 for 2007 versus 2000. Older age remained a predictor of use, with an odds ratio of about 7 for patients aged 80 years and older versus those aged 18 years to 39 years. Caucasian women were more likely to be treated with IAPBI than African American women, with an odds ratio of 1.3. Patients with DCIS or stage I disease were more likely to receive IAPBI (odds ratio of 1.9 for DCIS vs. stage II; odds ratio of 3.1 for stage I vs. stage II).

IAPBI Rates Increasing

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  2. IAPBI Rates Increasing
  3. Practice Implications

The results of this study confirm that IAPBI is being used more frequently as an adjuvant treatment after BCS. The authors conclude, however, that this rise is concerning because randomized controlled trials have not yet shown it to be equivalent to WBRT. Accelerated partial breast irradiation (APBI) can be delivered via several methods including balloon implantable catheters, interstitial brachytherapy, 3-dimensional conformal RT, and intraoperative RT.

Eleanor Harris, MD, clinical director of radiation oncology at the H. Lee Moffitt Cancer Center and Research Institute in Tampa, Florida, says there are no data regarding which APBI technique is preferable for any given patient.

APBI treats only the tissue around the tumor bed, resulting in higher doses per fraction because of the decreased tissue volume in the field. Most local recurrences occur near the original tumor site, even in patients who have undergone WBRT, making APBI logical.

There are, however, limited studies with long-term follow-up to show equivalence to WBRT. Dr. Abbott and colleagues wrote that to their knowledge, MammoSite is the most studied and probably the most frequently used balloon catheter for IAPBI. They note that the American Society of Breast Surgery's MammoSite registry is the largest cohort reported in the literature (Am J Surg. 2009;198:83-91). This registry shows a 2.15% rate of ipsilateral breast recurrence at 3 years of follow-up among 1440 patients. Four hundred patients with an additional year of follow-up showed a rate of 2.65%.

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Illustration 1. Depiction of the MammoSite applicator (Proxima Therapeutics Inc, Alpharetta, Ga) showing the radiation source port pathway, injection port, and balloon, which can be filled to a maximum of 70 cm3 or 125 cm3, depending on the model used.

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Despite these favorable data, the results of randomized clinical trials with long-term follow-up are not yet available. An ongoing trial of adjuvant RT after BCS in breast cancer patients with DCIS, stage I, or stage II disease randomizes women to WBRT or one of 3 types of APBI: 3-dimensional conformal RT (which is not an implantable technique), multicatheter, or MammoSite balloon catheter. Results of this trial will help clarify the efficacy of APBI. Dr. Harris says accrual will continue until about 2014, with early results expected around 2015.

The American Society for Radiation Oncology has published a consensus statement for APBI which outlines criteria for selecting women who may be suitable for APBI (Int J Radiat Oncol Biol Phys. 2009;74:987-1001). The statement proposes 3 patient groups: 1) a “suitable” group, for whom APBI outside of a clinical trial is acceptable; 2) a “cautionary” group, for whom caution and concern should be applied when considering APBI outside of a clinical trial; and 3) an “unsuitable” group, for whom APBI outside of a clinical trial should generally not be considered.

Benjamin Smith, MD, assistant professor of radiation oncology at The University of Texas MD Anderson Cancer Center in Houston, Texas, and lead author of the consensus statement, says retrospective studies published since the consensus was released have demonstrated low recurrence rates, even in patients who fell into the unsuitable category. Such studies warrant the inclusion of these patients in randomized studies to determine the safety and effectiveness of APBI, he adds.

Practice Implications

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  2. IAPBI Rates Increasing
  3. Practice Implications

Dr. Harris says APBI should only be used in select patients if given off study. “Patients not meeting criteria for suitable candidates should not be treated off study, but should be enrolled into a study such as [the] B-39 trial,” she says. Further, randomized data still have short follow-up and all patients need to be informed that there are no data demonstrating equivalence to WBRT over the long term, but that in appropriately selected patients, data from phase 2 studies and institutional series have 3- to 5-year results that seem acceptable.

Dr. Smith says that since the Early Breast Cancer Trialists' Collaborative Group meta-analysis demonstrated that RT after BCS did not confer a survival benefit in patients aged older than 60 years, it seems reasonable to offer alternatives to WBRT to this age group. “In general, I will consider APBI for women ages 60 and older with favorable disease characteristics, generally T1N0 without lymphovascular invasion or an extensive intraductal component,” he says.

According to Dr. Smith, patients need to know that WBRT has a long track record documenting its safety and effectiveness and that there is greater uncertainty regarding the long-term safety and effectiveness of APBI. “Clinicians need to be informed so they can help their patients make informed decisions,” he adds.