Interval cancers in breast cancer screening: comparison of stage and biological characteristics with screen-detected cancers or incident cancers in the absence of screening.
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.
Caumo
Francesca
F
Centro di Prevenzione Senologica, PO Marzana, ULSS 20, Verona, Italy.
Vecchiato
Francesca
F
Strabbioli
Marzia
M
Zorzi
Manuel
M
Baracco
Susanna
S
Ciatto
Stefano
S
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
D011960:Receptors, Estrogen; D011980:Receptors, Progesterone