Cancer incidence in countries representative of three patterns of reproductive cancer and age-specific mortality was used to estimate the effect of oral contraceptive use on the lifetime probability of reproductive cancer under three sets of assumptions about the effects of oral contraceptives. Under the set of assumptions considered likely, oral contraceptives were estimated to reduce or increase only slightly the lifetime probability of any reproductive cancer in each setting. Under worst-case assumptions, oral contraceptives were estimated to increase the lifetime probability of reproductive cancer only modestly in settings with low cancer rates and in settings with high rates of breast, ovarian, and endometrial cancer, but it might have a large impact on lifetime probability of reproductive cancer in settings with high cervical cancer rates. Under best-case assumptions, oral contraceptives were estimated to decrease the lifetime probability of reproductive cancer in each setting; this reduction was estimated to be greatest in settings where endometrial and ovarian cancer incidence are high.
PIP: Researchers applied published data on cancer incidence and age specific mortality to standard life table techniques to estimate the lifetime probability of developing reproductive cancer for women living in countries representative of 3 patters of risk of reproductive cancer and for long term oral contraceptives (OC) users under best case, worst case, and likely case assumptions. The reproductive cancers included breast, ovarian, endometrial, and cervical cancers. The data consisted of urban women from China, Japan, United States (California), England, Wales, Costa Rica, and Colombia. Under the likely case assumption, OCs just barely reduced or increased the lifetime probability of any reproductive cancer in any setting. Further, under the worst case scenario, OCs increased the lifetime probability or reproductive cancer moderately in countries with low cancer rates (Asian countries) and in countries with high rates of breast, ovarian, and endometrial cancer (Western Europe, North America, and Australia). Yet in countries with high cervical rates (South and Central America), OC use significantly affected the lifetime probability of reproductive cancer. The best case scenario revealed that OCs decreased lifetime probability of reproductive cancer in each country, especially those countries where endometrial and ovarian cancer incidences were great. The analysis also showed that OC use has the greatest effect on lifetime probability of reproductive cancer, be it positive or negative, in countries with high underlying rates of reproductive cancer. Further it demonstrated that the effect of OC use will most likely be small in countries with low incidence of reproductive cancers. Overall the researchers felt reassured about OC use and reproductive cancer. Even though long term OC use increases the risk of breast cancer in young ages.