Selective estrogen receptor modulators (SERM): Tamoxifen and raloxifene
Tamoxifen and raloxifene are SERMs, drugs that have divergent estrogen agonist and antagonist effects in different target organs. The association between endometrial cancer and tamoxifen was first recognized in 1985, when three cases of endometrial cancer were described in women who had been treated with tamoxifen for breast cancer. Since then, confirmation of the association has been provided by randomized clinical trials using tamoxifen for breast cancer treatment and prevention [52,53,54,55] and by case-control, observational, and laboratory studies.
The National Surgical Adjuvant Breast and Bowel Project, Breast Cancer Prevention Trial P-1 Study in women at high risk of invasive breast cancer demonstrated that tamoxifen decreased breast cancer incidence by 49%, but confirmed an increased incidence of endometrial cancer. The annual rate was 2.3 per 1,000 for women receiving tamoxifen versus 0.91 for those on placebo. Women older than 50 years experienced the largest effect. Of the 51 invasive cancers diagnosed in this trial, 50 were stage I.
Raloxifene is a second-generation SERM approved for prophylaxis against postmenopausal osteoporosis. Unlike tamoxifen, it does not have an estrogenic effect on the uterus. The Multiple Outcomes of Raloxifene randomized trial, after 40 months of follow-up, showed that raloxifene reduced the risk of estrogen receptor–positive breast cancer, without increasing endometrial cancer (RR = 0.8; 95% CI, 0.2–2.7). A population-based study of 547 women with endometrial cancer and 1,410 controls was done in Philadelphia, Pennsylvania. Of the cases, 18 (3.3%) had taken raloxifene and 34 (6.2%) had taken tamoxifen (OR = 3.0; 95% CI, 1.3–6.9).
Elevated BMI and obesity are associated with an increased risk of endometrial cancer. One of the possible mechanisms for the observed association is an increased level of serum estrone in obese women as a result of aromatization of androstenedione in adipose tissue, which increases the production of estrogen. Alternatively, obesity has been associated with a reduction in levels of SHBG, which may protect against endometrial cancer by decreasing bioavailable estrogen. Obesity has been associated with several factors known to increase the risk of endometrial cancer, including upper-body or central adiposity, polycystic ovarian syndrome, physical inactivity, and a diet high in saturated fat.
Presumably, body weight is a modifiable risk factor, which accounts for a substantial proportion of endometrial cases worldwide. A study conducted among European countries estimated that between 26% and 47% of endometrial cancer cases can be attributed to overweight and obesity. The same group conducted a meta-analysis of 12 studies (5 cohort and 7 case-control), which examined the relationship between obesity and endometrial cancer. Eleven of the 12 studies concluded that there is a positive association between endometrial cancer and excess weight.