Would you recommend adjuvant chemotherapy therapy to a premenopausal patient with ER+ lobular breast cancer who had a partial response to neoadjuvant endocrine therapy?

One approach is if you have enough tissue from the diagnostic core biopsy to run an Oncotype then base your decision on adjuvant chemo from that. This is assuming you are confident she is a N1 case (no treatment effects noted in other nodes). There is an ASCO 2018 abstract from Mayo (Talal Hilal et al) showing neoadjuvant endocrine therapy can drive up the RS score due to suppression of ER/PR RNA in treated samples compared to matched pretreatment samples. If that is not possible another approach is the data from Matt Ellis and Mitch Dowsett regarding the PEPI score (JCNI 2008). Those patients who were downstaged to ypT0-1N0 disease with a very low KI67 did the best. Those with residual node positive disease and a incompletely suppressed KI...

Results from TailoRx, MINDACT and other trials demonstrate that tumor biology is more important than most other prognostic factors in terms of estimating risk of distant recurrence and benefit of various adjuvant therapies, though we shouldn't toss out more traditional factors, such as stage, completely. In this case you have a patient whose cancer that responded to endocrine therapy but had residual disease in the breast and nodes at surgery. With the positive nodes, the PEPI score is going to be >0, which suggests that the patient would benefit from adjuvant chemotherapy. But I question that conclusion. While I might have done an Oncotype on the diagnostic biopsy upfront to decide whether the patient should receive neoadjuvant endocrine t...