Compared with women treated with whole-breast irradiation, those treated with brachytherapy experienced a twofold increased risk for subsequent mastectomy

Accelerated partial breast irradiation delivered by brachytherapy, the localized form of radiation therapy growing increasingly popular as a treatment choice for women with early-stage breast cancer, is associated with higher rate of later mastectomy, increased radiation-related toxicities and post-operative complications, compared to traditional whole breast irradiation, according to researchers from The University of Texas MD Anderson Cancer Center.

Comparison of radiation therapy techniques

The retrospective study was presented in the 2011 CTRC-AACR San Antonio Breast Cancer Symposium (December 6-10) by Dr Grace Smith, a resident in MD Anderson’s Department of Radiation Oncology and the study’s first author.

The study compared the two radiation therapy techniques available to women with early-stage breast cancer. The researchers found that women treated with accelerated partial breast irradiation therapy have a two-fold increased risk for subsequent mastectomy, most likely because of tumor recurrence or local complications, as well as an increased risk for post-operative and radiation-related complications.

There are numerous types of accelerated partial breast irradiation techniques; the MD Anderson study only looked at the brachytherapy technique, in which a specialized catheter containing radioactive source is surgically inserted into the cavity left behind after tumor removal. Accelerated partial breast irradiation by brachytherapy is performed a few weeks after a lumpectomy, twice daily over a course of five to seven days.

Brachytherapy technique has grown in popularity over the past decade

According to Dr Benjamin Smith, assistant professor at MD Anderson’s Department of Radiation Oncology, accelerated partial breast irradiation delivered by brachytherapy has grown in popularity over the past decade, since earlier studies showed generally low cancer recurrence rates, though most prior studies have not directly compared the outcomes of this technique to traditional radiation therapy.

The first commercially-available single catheter to deliver partial breast irradiation was approved by the FDA in 2002, escalating its use.

The MD Anderson study was based on analyzis of claim forms filed by 130,535 Medicare beneficiaries, who were diagnosed with cancer between 2000 and 2007.

The study authors found a consistent increase in accelerated partial breast irradiation delivered by brachytherapy, from less than 1% in 2000 to 13% in 2007.

There are benefits to the practicality brachytherapy offers

For whole breast irradiation, the standard treatment time is between five and seven weeks, but studies have shown that some women experience delays or have obstacles completing their course of radiation. Treatment delays and incompletion are known to increase the risk of cancer recurrence in the breast. Accelerated partial breast irradiation delivered by brachytherapy is attractive because it has the potential to address those issues, because treatment only lasts one week.

However, it’s also an invasive procedure with the greater potential for side-effects that are not associated with a non-invasive therapy, such as whole breast irradiation.

Retrospective population-based study

For the retrospective population-based study, the MD Anderson team examined the treatment history of women age 66 and older diagnosed with early-stage, invasive breast cancer between 2000 and 2007. All women were treated with breast-conserving surgery followed by either accelerated partial breast irradiation, delivered by brachytherapy, or traditional radiation therapy.

The researchers analyzed for effectiveness of radiation (defined as the need for a later mastectomy), post-operative complications (infectious and non-infectious), and post-radiation complications (breast pain, fat necrosis and rib fracture).

At five years, the incidence of mastectomy was statistically significantly higher in the brachytherapy group compared to that of the whole breast irradiation, 4% and 2.2%, respectively. Brachytherapy was also found to be associated with a higher incidence of acute and late toxicities, compared to those of whole breast irradiation – infectious complications, 16% and 10%, respectively; non-infectious complications, 16% and 8%, respectively; – and post-radiation complications – five-year incidence of rib fracture, 4% in both arms; fat necrosis, 9% and 4%, respectively; and breast pain, 15% and 12%, respectively.

Data limitations

The researchers noted the study’s limits, including that it was not randomized, the relatively-short follow up of patients and limited details available regarding tumor characteristics.

According to Dr Thomas Buchholz, professor and head of the Division of Radiation Oncology at MD Anderson, and also an author on the study, it is a very important, well-designed study in a large cohort of patients. It provides the first comparison of these two popular radiation techniques after breast-conserving surgery. In both groups, the authors found a relatively low risk of recurrence.

Any implication for the practice?

Randomized trials comparing accelerated partial breast irradiation, delivered by brachytherapy to the whole breast irradiation are ongoing. The authors noted about a need to discuss potential risks and benefits with patients, while awaiting definitive results from randomized trials. Practitioners at the MD Anderson Cancer Center will continue offering accelerated partial breast irradiation to interested patients in the context of ongoing institutional and multi-institutional clinical protocols.

Researchers did not expect that would find a difference in outcomes between brachytherapy and whole-breast irradiation using this claims-based approach. Such an approach has never been used before to evaluate breast brachytherapy. In any case, the study data underscore the importance of waiting for mature data from randomized clinical trials before widespread adoption of breast brachytherapy.

Source:ESMO.