Menstrual and reproductive factors in relation to risk of endometrial cancer in Chinese women

Reproductive risk factors for endometrial cancer among Polish women

We conducted a population-based case-control study of reproductive factors in Warsaw and Lódź, Poland, in 551 incident endometrial cancer cases and 1925 controls. The reproductive variable most strongly related to risk was multiparity, with subjects with three or more births having a 70% lower risk than the nulliparous women. The reduced risk was particularly strong below 55 years of age. Subjects with older ages at a first birth were also at reduced risk even after adjustment for number of births. Ages at last birth or intervals since last birth were not strongly related to risk. Spontaneous abortions were unrelated to risk, but induced abortions were associated with slight risk increases (odds ratios=1.28, 95% confidence intervals 0.8-2.1 for 3+ vs no abortions). The absence of effects on risk of later ages at, or short intervals since, a last birth fails to support the view that endometrial cancer is influenced by mechanical clearance of initiated cells. Alternative explanations for reproductive effects should be sought, including alterations in endogenous hormones.

Neoplasia with use of intrauterine devices

BACKGROUND

One of the mechanisms by which intrauterine devices (IUDs) prevent pregnancy is the creation of a sterile inflammatory response in the endometrium. Additionally, hormone-releasing IUDs or intrauterine systems (IUSs) release progestins or progesterone into the uterus. Both of these mechanisms may affect users' risk for neoplasia.

STUDY DESIGN

We searched the PubMed database for studies on IUD use and risk for neoplasia conducted between 1960 and September 2006 and published in all languages. We excluded case reports and case series. For the association between ever using an IUD and risk for endometrial cancer, we conducted a meta-analysis using a Bayesian random-effects model to account for between-study heterogeneity.

RESULTS

We found no evidence of increased risk for neoplasia with IUD use. Nine case-control studies and one cohort study found reduced risks for endometrial cancer with having ever used an IUD (pooled adjusted odds ratio=0.6, 95% confidence interval=0.4-0.7). No trend in associations was observed with characteristics of IUD use, type of IUD and histologic type of cancer. Four case-control studies found no association between IUD use and risk for cervical cancer. One study found no increased incidence of breast cancer among levonorgestrel-releasing IUS users as compared with the general population in Finland. Finally, three studies found no association between IUD use and occurrence of hydatidiform moles or malignant sequelae.

CONCLUSIONS

Use of an IUD does not appear to increase the risk for neoplasia. While nearly all studies found that IUD use was associated with a decreased risk for endometrial cancer, it remains unclear whether this association is causal.