The treatment of breast cancer was dominated by radical mastectomy or modified radical mastectomy of the affected breast prior to the 1970s. These included an en bloc removal of the breast, muscles of the chest wall, and contents of the axilla, and at the time they were advocated as the most appropriate local therapy for women with early-stage breast cancers. However, the results of the National Surgical Adjuvant Breast and Bowel Project (NSABP) B-06 and other studies found equivalent survival and local control rates among women treated with either mastectomy or lumpectomy followed by whole-breast irradiation (WBI).1,2 The NSABP B-06, which compared mastectomy to lumpectomy with and without radiotherapy in women with invasive carcinoma, found a 39% local recurrence rate at 20 years with lumpectomy alone, which was decreased to 14% with the addition of radiotherapy.1 Several other randomized studies demonstrated equivalent long-term survival and disease-free survival rates in patients treated by breast-conserving therapy (BCT) compared to mastectomy.2-5 Additional randomized studies comparing lumpectomy alone to lumpectomy and radiation clearly demonstrate a 3-fold reduction in local relapse with the use of radiation following breast-conserving surgery.6-10 More recent meta-analyses of trials comparing lumpectomy alone to lumpectomy and radiation demonstrated not only a 3-fold reduction in local relapse, but a small but statistically significant compromise in overall survival with the omission of radiation following lumpectomy.11,12 For patients with ductal carcinoma in situ (DCIS), randomized studies conducted by the NSABP and European Organization for Research and Treatment in Cancer (EORTC) comparing lumpectomy alone to lumpectomy and radiation found a 55% and 43% respective reduction in ipsilateral breast cancer events with the addition of radiotherapy.13,14 From these data, breast-conservation surgery followed by WBI (BCS+RT) became the standard of care for women with stage 0, I, and II breast cancer. BCS+RT involves the surgical removal of the primary tumor, evaluation of the axillary nodes, and local breast irradiation; this treatment is extremely well tolerated with minimal long-term toxicity and favorable cosmetic outcomes.15,16 Despite the obvious cosmetic and potential emotional advantages of BCS+RT, 15% to 30% of patients who undergo lumpectomy do not receive postoperative radiotherapy.17-20 Many patients may choose mastectomy or lumpectomy alone over BCS+RT due to the protracted course of daily treatment involved with WBI, which consists of daily radiotherapy to the whole breast for 25 treatments usually followed by a 5 fraction boost to the tumor bed, all delivered over the course of 6 to 6.5 weeks. Other reasons that steer women away from BCS+RT are physician bias, patient age, fear of radiation treatments, distance from a radiation treatment facility, and socioeconomic factors.18,21-24
Based on the numerous randomized studies noted above, it is standard of care for all women, regardless of age or tumor size, to receive radiotherapy in the setting of BCT to reduce local recurrence. However, in recent years investigators have tried to identify subsets of women ...