How long after lumpectomy for DCIS in a premenopausal patient can tamoxifen be started and still retain the benefit?

The TAM-02 trial showed that women with IDC who delayed taking tamoxifen 2 or more years after their diagnosis still did better than those who did not initiate it at all. You can extrapolate this data to ER+ DCIS as the protective benefit of estrogen blockade on breast tissue occurs whenever it is started.

If she has higher risk DCIS presentation I would consider asking her to take the tamoxifen for 18-24 months first then interrupt treatment to get pregnant. This is what is being done on the ongoing POSITIVE trial for IDC. The retrospective data on pregnancy post breast cancer presented by Dr. Lambertini is encouraging, but many of the ER+ women got some systemic therapy prior to conceiving. I prefer this approach, but would understand if s...