Trial Information

Swedish Mammography Cohort

From 1987 to 1990 a population-based mammography screening program was introduced in two
counties in central Sweden. In Västmanland County all women born between 1917 and 1948
received a mailed invitation to be screened by mammography between March 1987 and March 1989
(n=41,786) together with a 6-page questionnaire; 31,735 women (76%) returned the completed
questionnaires. In Uppsala County all women born between 1914 and 1948 were invited to the
screening and received the same questionnaire between January 1988 and December 1990
(n=48517); 34916 women (72%) returned the completed questionnaires. Hence, questionnaires
completed before undergoing mammography were obtained from 66,651 women (74%) in the source
population. These questionnaires included items about diet, parity, age at first child's
birth, history of breast cancer in family, weight, height, and education.

In 1997 a second questionnaire was sent to all cohort members who were still living in the
study area. The questionnaire updated information about diet and was extended to include
information on physical activity, medical history, age at menarche, history of oral
contraceptive use, age at menopause, postmenopausal hormone use and lifestyle factors such
as cigarette smoking history and use of dietary supplements. Majority of questions in the
questionnaires have been validated.

During 2008-09, the exposure information was updated and extended by sending out two new
questionnaires - one questionnaire on health including several signs of symptoms, sleeping,
social relations etc (2008) and one on diet, dietary supplement use, and lifestyle factors
(2009).

Incident cases of cancer are ascertained by record linkages of the study population with the
National Swedish Cancer Register and the Regional Cancer Registers. Cardiovascular and other
diseases as well as surgeries and causes of death are identified by linkage to the National
Inpatient and other registries at the Swedish Board of Health and Welfare. Ascertainment of
cancer cases and other diseases is almost 100% complete. Dates of deaths are ascertained
through the Swedish Death Register (100% complete), and information on date of moving out of
the study area is obtained by linkage with the Swedish Population Register.