Tamoxifen is now recommended for 10 years instead of just 5 for women
with hormone receptor–positive breast cancer, according to new
guidelines from the American Society of Clinical Oncology published in
the Journal of Clinical Oncology. Studies have shown improved survival
with extended tamoxifen, as well as reduced risk for recurrence and
contralateral breast cancer.

Women who are pre- or perimenopausal should begin with 5 years of
tamoxifen. After that, if they are still pre- or perimenopausal, they
should take tamoxifen for another 5 years. If they have become
postmenopausal, however, they should be given the choice of tamoxifen
or an aromatase inhibitor for 5 years.

Women who are postmenopausal at diagnosis should be offered the choice
of 10 years of tamoxifen, 5 years of an aromatase inhibitor, or either
2–3 or 5 years of tamoxifen followed by up to 5 years of an aromatase
inhibitor.

Journal of Clinical Oncology article