A woman's own characteristics at birth, such as her birth weight, and her mother's age at delivery may be related to her risk of early-onset breast cancer, according to a study of young women in the state of New York.1 Women whose birth weight was 4,500 g or more have triple the odds of developing breast cancer by age 38 compared with women whose birth weight was 2,500-3,499 g. In addition, women born to mothers aged 35 or older have twice the odds of developing breast cancer early in life of women whose mothers were aged 20-24 when they gave birth. By contrast, women who were born before 33 weeks of gestation or whose mothers had abruptio placentae have sharply decreased odds of developing breast cancer as a young person.

Using computerized vital record and cancer registry data, the researchers identified 2,391 women who were born after 1957 and who received a diagnosis of breast cancer between 1978 and 1995. Of these women, the investigators were able to match 484 to their birth records; they then matched this group with controls who had not received a diagnosis of breast or endometrial cancer and whose mothers had lived in the same county at the time of delivery. The women with cancer were predominantly white (87%); their age at diagnosis ranged from 14 to 37 years old.

The researchers examined the association between breast cancer risk and prenatal and perinatal characteristics that are either known or suspected to be related to maternal-fetal hormone levels or germ-cell mutations (which may affect the risk of breast cancer), including birth weight, gestational age, multiple birth, birth order, maternal and paternal age, and maternal race. They also evaluated possible assocations between breast cancer risk and maternal abruptio placentae (or premature detachment of the placenta), preeclampsia and eclampsia.

In conditional logistic regression analyses controlling for potentially confounding factors, the risk of early-onset breast cancer was elevated for women who had a high birth weight: Compared with women who were born weighing 2,500-3,499 g, those women who weighed 4,500 g at birth had a risk of breast cancer three times as high (odds ratio, 3.1).

In addition, the risk of early-onset breast cancer increased as maternal age increased: Compared with women who were born to mothers aged 20-24, women born to mothers 25-29 years old had 1.4 times the risk, those born to mothers in their early 30s had 1.5 times the risk, and those whose mothers were 35 or older had 1.9 times the risk. When all factors except maternal age were controlled for, there also was a linear increase in women's risk of early-onset breast cancer in relation to their father's age; women whose father was aged 40 or older had increased odds, compared with women whose father was aged 25-29 (odds ratio, 1.5). However, when paternal age was adjusted for maternal age, the association was not as strong.

Two factors were associated with a reduced risk of breast cancer: Women whose mothers had abruptio placentae and women who were born at a gestational age of less than 33 weeks had decreased odds of developing breast cancer at a young age (odds ratios, 0.2 and 0.1, respectively).

Black women had higher odds of breast cancer than white women (odds ratio, 1.9). Additional analyses showed that relative to young white women, young black women also had elevated odds of having advanced-stage disease (odds ratio, 2.1). First- or second-born black women had a particularly high breast cancer risk (odds ratio, 3.6).

The researchers acknowledge some limitations of their study--namely, that the state vital record and tumor registry data did not allow them to adjust for women's reproductive history, family history of breast cancer or body mass index. In addition, they were able to match only 38% of women who had breast cancer with their birth records. However, according to the researchers, these potential biases were not likely to have confounded their data.

Furthermore, the investigators note that the associations they found between high birth weight, older maternal age and the risk of early-onset breast cancer are consistent with findings indicating that intrauterine hormonal factors or germ-cell mutations may influence a woman's risk of developing breast cancer. Therefore, they conclude that their findings "offer further evidence that early life factors may be important determinants of early-onset breast cancer."--B. Brown


1. Innes K, Byers T and Schymura M, Birth characteristics and subsequent risk for breast cancer in very young women, American Journal of Epidemiology, 2000, 152(12):1121-1128.