How do you decide about neoadjuvant chemotherapy in a women with both IDC and DCIS on biopsy when the tumor is ill defined on imaging?

In the clinical scenario of a palpable tumor and biopsy reflecting a mix of pre-invasive disease (DCIS) and proliferative cancer, the value of neoadjuvant chemotherapy is debatable. The optimal goal of NAC is to ameliorate long term outcome, that was documented with pCR, these quite low in original studies, such as NSABP 18 and 27, with "all comers, and significantly higher when studies separated Her 2 positive disease and triple negative disease, (CTNeoBC analysis, Lancet 2014) where the proliferative, invasive pathology predominated.

Cytotoxic therapy would have no effect on DCIS . Even considering potential advantages of NAC vis a vis of decreasing the proportion of mastectomy into BCS for the same reason, the neoadjuvant approach wouldn'...

I would say the answer depends on the subtype of Invasive breast cancer. I would be fine considering Neo-adjuvant systemic therapy in the setting of TNBC and Her 2 Positive breast cancer as I would not be doing any harm even if invasive component is really small like only about 5 mm

I would not give Neo-adjuvant systemic therapy for Luminal A ( ER Positive/Her 2 Negative) subtype in this setting when size of invasive tumor is not certain, as there is a possibility of doing harm if we end up giving chemotherapy to a patient with small invasive tumor < 1cm or relatively larger tumor tumor T2/T3 where Genomic assays like Oncotype Dx would have shown no benefit from addition of chemotherapy.