What factors increase the risk of uterine cancer after breast cancer?

This article looked at the risks of developing uterine cancer in women who have survived breast cancer.

Uterine cancer (cancer of the uterus, or 'womb') is the most common gynaecologic tumor in women (tumors relating to the female reproductive organs). Certain factors associated with breast cancer can become risks for uterine cancer following survival from breast cancer. Tamoxifen (Nolvadex), a drug commonly used in breast cancer treatment, can be classified as one such risk factor.  Though tamoxifen hiners tumor growth, it is thought to have negative effects on the endometrium (the lining of the uterus). This can double the risk of developing uterine cancer in women who have been treated for breast cancer. 

The aim of this study was to determine the links between breast cancer and uterine cancer. A total of 7,229 breast cancer patients were surveyed. Furthermore, of these, 865 breast cancer patients who did not and 173 breast cancer patients who did later develop uterine cancer were directly compared. 

Of the 5,980 breast cancer patients who had not had a hysterectomy at the time of breast cancer diagnosis, 2.9% subsequently developed uterine cancer. The results showed that the long-term use of tamoxifen (over 5 years) increased the risk of developing uterine cancer by 95% (i.e. those who used tamoxifen for longer than 5 years had almost twice the risk of developing uterine cancer compared to those who did not use tamoxifen for longer than 5 years).

A history of high blood pressure increased the risk of uterine cancer (by 62%), as well as a history of gallbladder disease (30% increased risk) or thyroid disease (55% increased risk). Those who used estrogen-only hormone replacement therapy had almost two and a half times the risk of developing uterine cancer subsequent to breast cancer.  

The authors concluded that several risk factors exist that may help identify breast cancer patients and survivors who are at risk for uterine cancer, including high blood pressure, gallbladder disease, thyroid disease and long-term tamoxifen treatment.