The biologic rationale for and emerging role of accelerated partial breast irradiation for breast cancer.

Abstract

Breast-conserving therapy (BCT) has been established as a standard treatment for women with early-stage breast cancer. In six prospective randomized trials and in multiple retrospective studies in Europe and the US, BCT among patients with early-stage breast cancer has been found to result in survival equivalent to that observed after mastectomy. 1-9 Similarly, numerous studies have shown high rates of local tumor control with satisfactory cosmetic results with conservative surgery and irradiation. 2,7,8,10-14 Data from the National Surgical Adjuvant Breast and Bowel Project (NSABP) B-06 trial revealed 5-year recurrence within the breast in 28% of patients treated with lumpectomy alone but in only 8% of those who received postoperative breast irradiation. 15 Recent 20-year followup revealed a cumulative incidence of recurrent tumor in the ipsilateral breast of 14.3% in women who underwent lumpectomy and breast irradiation, as compared with 39.2% in women who underwent lumpectomy without irradiation. 16 In the NSABP B-06 trial and most other studies investigating BCT, radiation was delivered using standard whole-breast external-beam radiation therapy (EBRT) with or without a boost to the tumor-bearing region. Recently the need for whole breast radiation treatment (WBRT) after breast-conserving surgery (BCS) has become controversial, with some investigators advocating accelerated partial breast irradiation (APBI) as a potential alternative. APBI refers to radiation therapy that is delivered over a shorter period of time (“accelerated”) than the standard 5 to 6 weeks and is delivered to only a portion of the breast (“partial”). Since the early 1990s, investigators at multiple institutions have examined the safety and efficacy of APBI. One of the most used and investigated methods of APBI is brachytherapy. Brachytherapy permits delivery of high doses to small volumes encompassing the tumor bed while sparing surrounding tissues, including the skin, lung, and so forth. Although brachytherapy has been used for more than 80 years to treat breast cancer patients, only recently has it emerged as a possible sole radiation modality after lumpectomy in patients treated with BCT. In this review, we will examine the emerging role of brachytherapy in the treatment of early-stage breast cancer and address the biologic rationale for, advantages of, and possible limitations of brachytherapy as APBI after BCS. What’s wrong with whole-breast irradiation?