Extreme Prematurity and the Risk of Breast Cancer - A Cohort Study

Purpose: To analyze to what extent women born extreme premature and women characterized as small for gestational age at birth differ with regards to breast cancer risk as adults. Scope: To identify all women within a study base of 290,000 female births during the years 1925 to 1949 in central Sweden born before the 35th gestational week and/or with a birth weight below 2,000 grams. The women in the cohort still alive in 1958 have been followed up for occurrence of breast cancer through linkage with Swedish registries. Major findings: There were 1,847 survivors January 1, 1958, of which 90 were diagnosed with breast cancer up through 1996. Preliminary analyses strongly indicate that women born extremely premature compared to those born small for gestational age have an increased risk of breast cancer. Conclusion: Our findings strongly indicate that early hormonal exposures are of importance for the risk of breast cancer later in life.