In this project, associations between pregnancies and cancer risk will be examined. Focus will be on cancer forms known to be hormone-related, and also on some cancer types with less evidence for being susceptible to hormonal exposure. Our study is based on information from the Population register and the Cancer Registry of Norway, and comprises almost 2 million women at risk at ages 20-74 years. The possibility for performing large, population-based, prospective studies based on information from nationwi de registers is quite unique in the Scandinavian countries. Time-related effects of a pregnancy will be analyzed through a very detailed modeling of cancer risk in the years after a term birth. Maternal age at birth is also a factor that will be closely e xamined. The average age at first term birth has increased the last decades, and this may affect cancer incidence in either direction. Among women at the same age, those with children late in their reproductive life are also characterized by more recent c hildbirths. A methodological challenge is to distinguish between the effects of maternal age at birth and time since the birth in an age-adjusted model. A new analytical approach will be applied. Detailed analyses of breast cancer have already been perfor med, but some additional analyses of breast tumor characteristics according to reproductive history, will be carried out.
Results from this study will have importance at the public health level, as it will contribute to identifying high-risk groups or t ime periods. Results may also provide new insight into underlying biological mechanisms for the observed associations. Such knowledge is quite valuable in further treatment, as well as prevention of disease. Clinicians and other researchers, working in th e field of cancer prevention and treatment, can utilize the results from this study.