What would be your choice of endocrine therapy (if any) for a premenopausal woman with an ER positive 2nd DCIS in ipsilateral breast who has completed 5 years of tamoxifen after lumpectomy of 1st DCIS?

The original DCIS was 10 years ago and Tamoxifen was given to prevent a local recurrence and a new primary. We have data that tamoxifen can have beneficial effects for at least 5 years after discontinuation. GIven that this is the second primary the first thing would be to check her genetics. THat m...