What adjuvant therapy would you recommend for a premenopausal patient with ER/PR+, HER2 negative T2N0 breast cancer s/p mastectomy, low OncotypeDx score and in first trimester of pregnancy?

I would favor no adjuvant therapy until post-partum when she can transition to Tamoxifen.

I agree that definitely no systemic therapy during the first trimester of pregnancy, regardless of whether it is chemotherapy or endocrine therapy. Endocrine therapy should also be avoided, in general, during pregnancy due to concerns for inducing premature delivery or miscarriage, vaginal bleeding,...