How do you approach treatment in premenopausal patients who develop a contralateral HR+ breast cancer while already on tamoxifen and ovarian function suppression?

Several pieces of information are lacking in this clinical case to make a solid treatment recommendation: what is the current age of the patient? What is her menopausal status? Is the new contralateral breast cancer clinically node negative?

Since this new second primary contralateral breast cancer ...

If she doesn't need adjuvant chemo after surgery, I would switch her to OFS+AI for at least 5 years.