title: Tumor characteristics associated with mammographic detection of breast cancer in the Ontario breast screening program.
abstract: BACKGROUND
  Few studies have compared the prognostic value of tumor characteristics by type of breast cancer diagnosed in the interval between mammographic screenings with screen-detected breast cancers.
  
  
  METHODS
  We conducted a case-case study within the cohort of women (n = 431 480) in the Ontario Breast Screening Program who were aged 50 years and older and were screened between January 1, 1994, and December 31, 2002. Interval cancers, defined as breast cancers diagnosed within 24 months after a negative screening mammogram, were designated as true interval cancers (n = 288) or missed interval cancers (n = 87) if they were not identified at the time of screening but were identified in retrospect. Screen-detected breast cancers (n = 450) were selected to match interval cancers. Tumors were evaluated for stage, grade, mitotic index, histology, and expression of hormone receptors and odds ratios (ORs) and 95% confidence intervals (CIs) were calculated by conditional logistic regression.
  
  
  RESULTS
  Both true and missed interval cancers were of higher stage and grade than matched screen-detected breast cancers. However, true interval cancers had a higher mitotic index (OR = 3.13, 95% CI = 1.81 to 5.42), a higher percentage of nonductal histology (OR = 1.94, 95% CI = 1.05 to 3.59), and were more likely to be both estrogen receptor-negative (OR = 2.09, 95% CI = 1.32 to 3.30) and progesterone receptor-negative (OR = 2.49, 95% CI = 1.68 to 3.70) compared with matched screen-detected tumors.
  
  
  CONCLUSIONS
  In this study, interval cancers were of higher stage and grade compared with screen-detected cancers. True interval cancers were more likely to have additional adverse prognostic features of estrogen and progesterone receptor negativity and nonductal morphology. The findings suggest a need for more sensitive screening modalities to detect true interval breast cancers and different approaches for early detection of fast-growing tumors.
authors.affiliation: Prevention and Cancer Control, Cancer Care Ontario, 620 University Ave, Toronto, ON M5G 2L7, Canada. anna.chiarelli@cancercare.on.ca
authors.forename: Victoria A
authors.initials: VA
authors.lastname: Kirsh
authors.forename: Anna M
authors.initials: AM
authors.lastname: Chiarelli
authors.forename: Sarah A
authors.initials: SA
authors.lastname: Edwards
authors.forename: Frances P
authors.initials: FP
authors.lastname: O'Malley
authors.forename: Rene S
authors.initials: RS
authors.lastname: Shumak
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Yaffe
authors.forename: Norman F
authors.initials: NF
authors.lastname: Boyd
mesh_terms: D000368:Aged; D014408:Biomarkers, Tumor / Q000032:analysis; D001943:Breast Neoplasms / Q000737:chemistry / Q000000981:diagnostic imaging* / Q000473:pathology*; D016022:Case-Control Studies; D015986:Confounding Factors, Epidemiologic; D055088:Early Detection of Cancer; D005260:Female; D006801:Humans; D016015:Logistic Models; D008327:Mammography; D008403:Mass Screening / Q000379:methods*; D008875:Middle Aged; D016017:Odds Ratio; D009864:Ontario; D011237:Predictive Value of Tests; D011379:Prognosis; D011960:Receptors, Estrogen / Q000032:analysis; D011980:Receptors, Progesterone / Q000032:analysis; D012107:Research Design; D012307:Risk Factors; D011795:Surveys and Questionnaires
chemical_list: D014408:Biomarkers, Tumor; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone