title: Incomplete pregnancy is not associated with breast cancer risk: the California Teachers Study.
abstract: BACKGROUND
  Early studies of incomplete pregnancy and development of breast cancer suggested that induced abortion might increase risk. Several large prospective studies, which eliminate recall bias, did not detect associations, but this relationship continues to be debated.
  
  
  METHODS
  To further inform this important question, we examined invasive breast cancer as it relates to incomplete pregnancy, including total number of induced abortions, age at first induced abortion and total number of miscarriages among women participating in the ongoing California Teachers Study (CTS) cohort. Incomplete pregnancy was self-reported on the CTS baseline questionnaire in 1995-1996. Incident breast cancers were ascertained in 3324 women through 2004 via linkage with the California Cancer Registry.
  
  
  RESULTS
  Using Cox multivariable regression, we found no statistically significant association between any measure of incomplete pregnancy and breast cancer risk among nulliparous or parous women.
  
  
  CONCLUSIONS
  These results provide strong evidence that there is no relationship between incomplete pregnancy and breast cancer risk.
authors.affiliation: Department of Cancer Etiology, City of Hope Comprehensive Cancer Center, Duarte, CA 91010, USA. khenderson@coh.org
authors.forename: Katherine DeLellis
authors.initials: KD
authors.lastname: Henderson
authors.forename: Jane
authors.initials: J
authors.lastname: Sullivan-Halley
authors.forename: Peggy
authors.initials: P
authors.lastname: Reynolds
authors.forename: Pamela L
authors.initials: PL
authors.lastname: Horn-Ross
authors.forename: Christina A
authors.initials: CA
authors.lastname: Clarke
authors.forename: Ellen T
authors.initials: ET
authors.lastname: Chang
authors.forename: Susan
authors.initials: S
authors.lastname: Neuhausen
authors.forename: Giske
authors.initials: G
authors.lastname: Ursin
authors.forename: Leslie
authors.initials: L
authors.lastname: Bernstein
mesh_terms: D000028:Abortion, Induced / Q000706:statistics & numerical data*; D000022:Abortion, Spontaneous / Q000453:epidemiology; D000328:Adult; D001943:Breast Neoplasms / Q000453:epidemiology*; D002140:California; D015984:Causality; D015331:Cohort Studies; D005178:Faculty; D005260:Female; D006801:Humans; D008875:Middle Aged; D011247:Pregnancy; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012307:Risk Factors; D011795:Surveys and Questionnaires