How would you approach a patient with T3 HR+,HER2- breast cancer who had no clinical improvement after ddAC?

This is one of those questions where I wish I had a tiny bit more information about the decision-making behind electing NAC. For instance, was this breast cancer grade 3, with a high Ki-67 and ER 25% PR ngtv? Or was this patient a very borderline candidate for breast-conservation and motivated enough to elect potentially unnecessary chemotherapy in the hope of avoiding mastectomy? Presumably, this patient was started on ddAC with an intention of proceeding to weekly or dd paclitaxel followed by surgery, with the primary motivation of reducing her risk of distant recurrence.

The question implies that this is a T3 N0 HR+ and HER2- cancer, and many might recommend surgery first in the hopes that surgery and possible 21-gene assay could spare t...

While I agree that additional information would be helpful, would add a few comments. In NSABP B-27, patients who did not have a clinical response to AC did not benefit—in terms of pCR rate or DFS—to subsequent treatment with docetaxel (in contrast to clinical PR patients who did); and it is unlikely that subsequent treatment with a taxane is going to induce a sufficient response to convert such a patient from requiring a mastectomy to being a candidate for BCS. However, it would be easier to justify administering subsequent chemotherapy to a patient with palpable N1 (much less N2-3) disease, or a patient with low ER expression (who I might treat with weekly paclitaxel/carboplatin like TNBC), for its potential distant DFS benefit.