title: Clinical stage of breast cancer by parity, age at birth, and time since birth: a progressive effect of pregnancy hormones?
abstract: Breast cancer diagnosed during pregnancy or 1 to 2 years after birth often occurs at a late stage. Little is known about tumor characteristics in the high-risk period shortly after a childbirth. We here explore whether stage of disease differs according to timing of births. Results are based on 22,351 Norwegian breast cancer patients of parity 0 to 5, ages 20 to 74 years. The proportion of stage II to IV tumors was considerably higher among parous than nulliparous women at age <30 years (52.7% versus 36.8%, P=0.009), but similar or lower in other age groups (P(interaction)=0.029). In general, the largest proportion of stage II to IV tumors was found among women diagnosed during pregnancy or <2 years after birth. However, among women with late-age births (first or second birth >or=30 years, third birth >or=35 years), as well as women with an early second birth (<25 years), the proportion with advanced disease was rather similar or even higher among those diagnosed 2 to 6 years after birth (49.3-56.0%). The association between clinical stage and time since birth reached statistical significance among women with a late first or second birth and among all triparous women (P <or= 0.032). The subgroups with a high proportion of advanced disease 2 to 6 years after birth corresponded quite well to those previously found to have the most pronounced transient increase in risk after birth. Thus, pregnancy hormones may have a progressive effect on breast cancer tumors in addition to a possible promoting effect. A potential effect of prolactin is discussed.
authors.affiliation: Department of Mathematics, Center for International Health, University of Bergen, Bergen, Norway. msega@uib.no
authors.forename: Grethe
authors.initials: G
authors.lastname: Albrektsen
authors.forename: Ivar
authors.initials: I
authors.lastname: Heuch
authors.forename: Steinar
authors.initials: S
authors.lastname: Thoresen
authors.forename: Gunnar
authors.initials: G
authors.lastname: Kvåle
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D001721:Birth Intervals; D001943:Breast Neoplasms / Q000473:pathology*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008423:Maternal Age; D008875:Middle Aged; D009367:Neoplasm Staging; D009664:Norway; D010298:Parity; D011247:Pregnancy; D011252:Pregnancy Complications, Neoplastic / Q000473:pathology; D011446:Prospective Studies; D017584:Reproductive History; D012307:Risk Factors