Would you offer RNI for young patient with cT3N0 triple negative breast cancer that had progression of disease during neoadjuvant chemotherapy, followed by mastectomy and sentinel node biopsy?  

Yes, without hesitation. The primary randomized data suggesting an improvement in overall survival (OS) with PMRT in the T3N0 setting included RNI (e.g. Overgaard et al., PMID 9395428). There is also a study of +/- PMRT (including regional nodes) in T3 patients (about 40% of which were T3N0), that a...

I usually favor PMRT with RNI for clinical T3 No treated with NACT unless pCR then discuss the pros and cons.

I would offer PMRT (including RNI) in this case for multiple reasons, primarily due to the large size/T3 (citations above). But combined with progression during chemo in a premenopausal patient with triple negative disease…no question. 

Short answer: Yes. Progression through chemotherapy is a poor prognostic indicator and therefore, PMRT + RNI should be given.  Long answer: T3N0 represents a spectrum of disease in breast cancer and unfortunately, there will never be clinical evidence that specifically addresses every risk...