A Follow-up Study of Women Evaluated and Treated for Infertility

Overview

To assess the relations of infertility causes and treatment to cancer risk, we will conduct a retrospective cohort study of approximately 12,000 women evaluated for infertility between 1965-1988. These women will be ascertained from several large infertility clinics and private practices in various geographic locations in the United States: Boston, Chicago, Detroit, New York, and Palo Alto. These practices were selected on the basis of their having large number of patients who received ovulation stimulating drugs many years in the distant past. Abstractors reviewed clinic medical records to identify eligible study participants and abstract data needed to classify causes of infertility and document therapies employed. Using a variety of tracing sources (including the National Death Index, credit bureaus, and postmasters), the vital status and location of the study subjects were determined. Subjects who were traced and identified as alive are being sent a detailed questionnaire that requests information on their health status as well as on a number of lifestyle practices. For subjects who report a cancer, medical verification is being sought from the diagnosing physicians and/or facilities. Death certificates are being sought for deceased subjects.

BACKGROUND: We previously conducted a retrospective cohort study of 12,193 patients evaluated for infertility between 1960-1988 at five clinical sites. Detailed information abstracted from the medical records, along with questionnaires administered to located patients and cancer incidence and mortality data derived from cancer registries and the National Death Index, allowed us to examine cancer risk related to different causes of infertility and treatments while controlling for other patient characteristics. Although there were some increases of certain cancers related to various causes of infertility, we generally did not observe substantial relationships related to use of different fertility drugs. The one exception was some increased risk of uterine cancers with clomiphene use, of interest given the drug's chemical similarity to tamoxifen. Our numbers of patients with certain cancers (e.g., ovarian, uterine) were, however, limited and we had insufficient power to evaluate subgroup effects (e.g., drug relationships among nulligravid women). OBJECTIVES: We therefore conducted an updated follow-up of these patients in order to assess cancer risk in relation to causes of infertility and therapeutic regimens used to treat these causes. ELIGIBILITY: This study gained an additional 10 years of follow-up among the patients deemed eligible for the previous investigation. This included women with both primary and second infertility. Approximately 39% of the cohort previously were prescribed clomiphene citrate, while 10% received gonadotrophins. DESIGN: Passive follow-up was attempted for patients who previously did not participate and for whom only information available in clinic records could be retained. All other patients were traced for active as well as passive follow-up. Active follow-up involved requesting that patients complete a short questionnaire, whereas passive follow-up was via linkage to cancer registries and the National Death Index. While cancer risks were assessed in relation to the general population, the majority of comparisons were internal ones, involving the calculation of relative risks (RRs) associated with different causes of infertility or treatment regimens while controlling for other cancer risk predictors.