The following article features coverage from the San Antonio Breast Cancer Symposium (SABCS) 2018 meeting. Click here to read more of Cancer Therapy Advisor‘s conference coverage.

The results of partial-breast irradiation (PBI) after lumpectomy for patients with early-stage breast cancer were not equivalent to the outcomes of those who underwent whole-breast irradiation (WBI) for the control of ipsilateral breast tumor recurrence (IBTR), according to results from the NSABP B-39/RTOG 0413 study, which were presented at the 2018 San Antonio Breast Cancer Symposium in San Antonio, Texas.

However, the researchers noted that the absolute difference in the 10-year rate of IBTR was less than 1% between the 2 radiation approaches. 

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According to the study, WBI after lumpectomy is known to reduce the risk for IBTR so that is nearly similar to the risk associated with undergoing mastectomy. An alternative approach, PBI, treats only the tumor bed area, where a majority of IBTRs are known to occur. This trial was designed to test the equivalence of PBI with WBI in women with stage 0, I, or II breast cancer.

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The trial included 4216 patients who were randomly assigned to PBI or WBI. With a median follow-up longer than 10 years, 161 IBTRs occurred: 90 in the PBI group and 71 in the WBI group (hazard ratio [HR] = 1.22; 90% confidence interval [CI], 0.94-1.58). This result failed to meet the protocol-defined margin for equivalence, which was a 90% CI that was between 0.667 and 1.5. 

The majority of patients assigned to PBI and WBI were IBTR-free at 10 years (95.2% vs 95.9%, respectively). In addition, there was no difference in distant disease-free interval, overall survival, or disease-free survival between the 2 groups. However, the 10-year recurrence-free interval favored WBI (91.9% vs 93.4%; HR = 1.32, 95% CI, 1.04-1.68; = .02). 

Finally, grade 3 toxicity occurred in 9.6% of patients assigned PBI compared with 7.1% of those who were assigned WBI. 

Read more of Cancer Therapy Advisor‘s coverage of the SABCS 2018 meeting by visiting the conference page.


  1. Vicini FA, et al. Primary results of NSABP B-39/RTOG 0413 (NRG Oncology): A randomized phase III study of conventional whole breast irradiation (WBI) versus partial breast irradiation (PBI) for women with stage 0, I, or II breast cancer. Presented at the 2018 San Antonio Breast Cancer Symposium; Dec. 3-8; Abstract GS4-05.