title: Interval cancers in breast cancer screening: comparison of stage and biological characteristics with screen-detected cancers or incident cancers in the absence of screening.
abstract: OBJECTIVE
  To analyze stage distribution and biological features of interval cancers observed in Verona mammography screening compared to screen-detected cancers and "clinical" cancers occurring in the absence of screening, as provided by the Veneto Cancer Registry.
  
  
  METHODS
  Screen-detected cancers were identified in the screening archives. Interval cancers and clinical cancers (occurring in women never screened or not yet invited) were identified through the local cancer registry. Studied variables were age, stage, pathological pT and pN category, histological grading, estrogen and progesterone receptor status, and proliferation index (Ki67).
  
  
  RESULTS
  We compared 95 interval cancers, 761 screen-detected cancers, and 1873 clinical cancer cases. Interval cancers had more aggressive features than screen-detected cancers, the difference being statistically significant for pT (P=106), pN (P = 0.0003), grading (P = 0.007), estrogen receptors (P = 0.0006), and progesterone receptors (P = 0.00005), but not for Ki67 (P = 0.18). The features of interval cancers were not more aggressive than those of clinical cancers for pT (P = 0.84), pN (P = 0.33), grading (P = 0.61), estrogen receptors (P = 0.48), and progesterone receptors (P = 0.69), and were better for Ki67 (P = 0.02). In contrast, screen-detected cancers showed significantly better features than clinical cancers, for all studied variables: pT (P = 10(-6)), pN (P = 10(-6)), grading (P = 10(-6)), estrogen receptors (P = 10(-5)), progesterone receptors (P = 10(-6)), and Ki67 (P = 10(-6)).
  
  
  CONCLUSIONS
  Our findings are consistent with the length biased sampling hypothesis of interval cancers having a faster growth rate and a less favorable presentation than screen-detected cancers. Compared to clinical cancers, interval cancers had similar features, whereas screen-detected cancers had definitely more favorable features. This finding suggests, rather than a faster growth rate for interval cancers, a slower growth rate for screen-detected cancers, which, together with diagnostic anticipation, may explain a certain degree of overdiagnosis.
authors.affiliation: Centro di Prevenzione Senologica, PO Marzana, ULSS 20, Verona, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Caumo
authors.forename: Francesca
authors.initials: F
authors.lastname: Vecchiato
authors.forename: Marzia
authors.initials: M
authors.lastname: Strabbioli
authors.forename: Manuel
authors.initials: M
authors.lastname: Zorzi
authors.forename: Susanna
authors.initials: S
authors.lastname: Baracco
authors.forename: Stefano
authors.initials: S
authors.lastname: Ciatto
mesh_terms: D000368:Aged; D001943:Breast Neoplasms / Q000737:chemistry / Q000000981:diagnostic imaging / Q000473:pathology*; D005260:Female; D006801:Humans; D008327:Mammography; D008875:Middle Aged; D009367:Neoplasm Staging; D011960:Receptors, Estrogen / Q000032:analysis; D011980:Receptors, Progesterone / Q000032:analysis
chemical_list: D011960:Receptors, Estrogen; D011980:Receptors, Progesterone