DESCRIPTION: (Adapted from Applicant's Abstract). A full-term pregnancy
may have two opposing effects on breast cancer risk: 1) an adverse one
shortly after delivery; and 2) a beneficial one in the long term. These
effects could be due to group-enhancing consequences of the elevated
pregnancy hormones on already initiated cells, superimposed on the long-term
protective effect brought about by pregnancy-induced terminal
differentiation of the susceptible mammary gland cells. The relations
between birth characteristics and the risk and prognosis of postpartum
maternal breast cancer have not been adequately examined. The plan is to
study these relations in a database that links together the Swedish Medical
Birth Registry, National Cancer Registry, and Registry of Causes of Death.
Study questions include whether delivery of a large size child or a multiple
birth (indicators of high levels of pregnancy hormones), a pre-term baby, a
small-for-date baby or one with low Ponderal index (indicators of growth
retardation), affect maternal risk of breast cancer, whether preeclampsia
during pregnancy (indicator of placental dysfunction) affects postpartum
breast cancer, whether breast cancers diagnosed shortly after delivery have
a different prognosis compared to those diagnosed after a longer period
after delivery, and whether gender of the child predicts the prognosis of
breast cancers diagnosed shortly after delivery. Cases are more than 5,000
women who had one or more childbirths between 1973 and 1992 and who had a
breast cancer diagnosis during the same period. To study risk factors, for
each case subject, five controls will be randomly selected from among those
who were in the source population during the same period, were alive at the
date of the diagnosis of the index case, and had not been diagnosed with
breast cancer by that date. The controls will be matched to the case on
birth year and birth month. Standard statistical methods for a matched
case-control study will be applied to examine birth characteristics as risk
determinants of postpartum breast cancer and standard methods for survival
analysis will be applied to examine birth characteristics as prognostic
factors among those diagnosed with breast cancer after a childbirth.
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