http://www.nhs.uk/news/2012/12December/Pages/Ten-years-of-tamoxifen-ups-cancer-survival-rates.aspx
Tamoxifen is commonly offered alongside other breast cancer treatments and it is usually recommended that treatment with the drug continues for five years after other treatments have ended. This is because research has found that a long-term course of tamoxifen can reduce the risk of breast cancer returning (recurrence) and can also help prevent breast cancer deaths. The researchers thought that extended treatment for 10 years may offer further benefits. They did in fact find that cancer recurrence was lower in women receiving 10 years of treatment compared with women getting the standard five years of treatment.
