In light of the NSABP B-51 data presented at SABCS, will you defer RNI in all patients with negative nodes after chemotherapy?

Results of the NSABP B-51 trial were presented at the 2023 San Antonio Breast Cancer Symposium (Mamounas et al., abstract GS-02-07). This trial was designed to test the value of postoperative radiation therapy in patients who presented with clinical T1-3N1 tumors with biopsy-proven axillary node involvement who had pathologically negative nodes (ypN0) on either sentinel node biopsy (SNB) or axillary lymph node dissection (ALND) after neoadjuvant chemotherapy (NACT). Of importance, the treatment arms varied according to the type of surgery. Those who underwent mastectomy (42% of the population) were allocated to either observation or postmastectomy radiation therapy (PMRT) including the chest wall or reconstructed breast and regional nodal i...

B51 has the potential to be a practice-changing trial! I agree with much of what Dr. @Dr. First Last writes in his thoughtful summary and commentary.

To briefly summarize eligibility, the trial enrolled women with clinically node-positive disease (cT1-3 N1), who received NAC and had a pathologic complete response (CR) in the axilla (+/- path CR in the breast). Lumpectomy patients were randomized to whole breast irradiation (WBI) vs. WBI + regional nodal irradiation (RNI). Mastectomy patients were randomized to no RT vs. PMRT (chest wall +RNI).

Who was actually enrolled? Good age distribution (~40% of patients were <= age 49), race/ethnicity distribution (~18% Af Am/14% Hispanic), most T2 sized (60%) w/ ~20% T3. Lumpectomy/Mastectomy split 60/...

Dr. @Dr. First Last's and @Dr. First Last's write-ups above are noteworthy and thoughtful. As Dr. @Dr. First Last notes, the majority of patients here (80%) had pathCR in the breast and nodes, suggesting that practitioners were preferentially enrolling patients they felt were at very low risk of RT omission. The inclusion of ALND was simply a matter of practice patterns in 2010-2012 when the study was being designed.

At a basic level, I would caution against over-interpretation of the Forest plots. The events are low and the findings could easily be spurious. With that being said, between the two extremes of "this is only 5 years of data, abstract only, and too many question marks in the subgroups, hence I plan to continue irradiating all p...

For stage II patients with pCR in the node, I recommended pMRT or RNI specifically for triple-negative cases. In stage III (T3N1) scenarios with pCR, I recommend pMRT or RNI to all patients. Given this data, I'll need to reassess the standard treatment for these two subsets.

It's worth noting that there are plans for further analysis and extended follow-up of this study.