Role of radiation therapy in breast conservation therapy

INTRODUCTION

With the emergence of breast conservation therapy (BCT), women with invasive breast cancer may now preserve their breast without sacrificing oncologic outcome. The successful application of BCT requires collaboration between surgeons, radiologists, pathologists, and radiation and medical oncologists.

Adjuvant radiation therapy (RT) after BCT will be reviewed here. Surgical techniques of mastectomy and BCT and postmastectomy radiation therapy (RT) are discussed elsewhere. (See "Mastectomy and breast conserving therapy for invasive breast cancer" and "Postmastectomy chest wall irradiation", ).

LOCAL RECURRENCE AND THE ROLE OF RT IN BCT

Despite the equivalence in overall survival with MRM and BCT, breast conservation would have limited appeal if high local recurrence rates resulted in a significant number of subsequent mastectomies. The degree of residual disease in the breast after surgery alone is significant, as illustrated by a detailed evaluation of mastectomy specimens using radiography of thin (5 mm) sections and histologic examination of an average of 20 blocks per specimen [1]. Residual microscopic cancer >2 cm from the tumor was found in 41 percent of patients (two-thirds of which was intraductal and one-third invasive); this disease would be left behind after a standard lumpectomy. The percentage of women with residual cancer (either invasive or intraductal) >2 cm from the reference tumor corresponds well to the local failure rate in women with invasive breast cancer undergoing excision alone [2-6].

RT is an essential component of BCT to eradicate these subclinical deposits. Modern RT techniques that deliver between 45 to 50 Gy to the entire breast over 4.5 to 5 weeks provide adequate control of microscopic residual disease, permit the preservation of a cosmetically satisfactory breast, and improve survival [3,7-17]. The contribution of RT to outcomes can best be illustrated by the following:

• In the NSABP B-06 trial that included treatment arms for lumpectomy with or without RT; the incidence of recurrent tumor in the ipsilateral breast was significantly less in the radiated group (14 versus 39 percent at 20 years) [3].
• In a meta-analysis that included 10 randomized trials comparing conservative surgery alone or with RT, the absolute reduction in breast recurrence rates with RT was 17 percent for women with node-negative disease (25 versus 8 percent) and 19 percent for the node-positive group (35 versus 16 percent) [7].
• A survival benefit for RT as a component of BCT was shown in the most recent update of the Early Breast Cancer Trialists Collaborative Group (EBCTCG) meta-analysis [17]. Among 7300 women enrolled in trials of BCT with and without RT, the 15-year breast cancer mortality risks were significantly lower in the irradiated group (30.5 versus 35.9 among controls, p = 0.002).