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Introduction There is considerable evidence that the use of an intrauterine device (IUD) is associated with a decreased risk for endometrial cancer and some data that it may also lower ovarian cancer risk. The latter data indicate that IUD use may be part of a set of exposures which might lower ovarian cancer risk by inducing an inflammatory reaction in tissues that express the surface gylcoprotein and tumor antigen MUC1, exposing an unglycosylated form of MUC1 to immune recognition, and leading to the formation of protective anti-MUC1 antibodies. In this abstract, we examine the association between IUD use and ovarian cancer risk in a larger case-control data set and in greater detail than in our initial presentation of this association. Methods These data are from two phases of an ongoing population based ovarian cancer case control study. We identified ovarian cancer cases through hospital tumor boards and statewide cancer registries in New Hampshire and eastern Massachusetts between 1992 and 2003. We identified controls through a combination of random digit dialing, town book selection, and use of drivers' license lists. We enrolled a total of 1231 epithelial ovarian cancer cases and 1244 controls. We interviewed all participants in person on a variety of reproductive and lifestyle characteristics. Anti-Muc1 antibodies were measured against a synthetic 100-mer MUC1 peptide corresponding to five tandem repeats of the MUC1 polypeptide core tandem repeat region in controls only from phase II. We calculated odds ratios (OR) and 95% confidence intervals (CI) using unconditional logistic regression. Risk for ovarian cancer associated with various descriptors of IUD use was calculated for all ovarian cancer cases and various histologic subtypes. Likelihood of antibodies (restricted to the phase 2 controls) was also assessed by the same descriptors of IUD use. Results Overall we observed an inverse association between IUD use and ovarian cancer risk (OR = 0.71, 95% CI: 0.56, 0.89). The association was attenuated when we additionally adjusted for parity, tubal ligation, and oral contraceptive use (covariate-adjusted OR= 0.86, 95% CI: 0.68, 1.08). Duration of IUD use had a U-shaped association with ovarian cancer risk. Women who had an IUD for <=1, 2-3, 4-7, or >7 years had 0.72, 0.66, 0.61, and 0.84 times the risk of ovarian cancer as a women who never had an IUD, respectively. Similarly, the protective effect of IUD use was attenuated for women in the oldest age group at first IUD placement (>30 years). In general the likelihood of antibodies tracked in a manner similar to the odds ratios. Examination by histologic type revealed the strongest association to pertain to endometrioid tumor types (OR=0.40, 95% CI: 0.22, 0.71). Conclusions IUD use reduces the risk of ovarian cancer, especially for endometrioid types of ovarian cancer. The protective effect may be attenuated with older age at first use and longer lifetime duration of use.

[Proc Amer Assoc Cancer Res, Volume 47, 2006]