Endometrial cancer is an increasingly common gynecologic cancer in Japanese women; the age-standardized incidence rate increased from 1.4 to 7.3 between 1975 and 2005.1 Interestingly, a marked difference in age-specific incidence has been observed among women older than 50 years.1 Obesity is an important established risk factor for endometrial cancer,2,3 with many studies showing that current obesity is associated with increased risk for endometrial cancer due to the effect of adiposity on the synthesis and bioavailability of endogenous sex steroid hormones, mainly estrogens.4–8. This evidence concerns the gene PLXNA3 and obesity due to melanocortin 4 receptor deficiency.