In women with cN0 breast cancer who receive neoadjuvant chemotherapy due to other high-risk features, how does the finding of treatment effect in a post-chemo sentinel lymph node affect your radiation recommendations?  

Women with cN1 disease at diagnosis who are ypN0 after neoadjuvant chemo can be randomized on NSABP B-51, but not those with cN0 disease and treatment effect in a sentinel lymph node. Presumably, if the SLNBx had taken place prior to chemo, these cN0 patients would have had pN1 disease. Should the undissected axilla be radiated? Should these patients receive regional nodal irradiation even with lateralized primary tumors?