Pathology characteristics that optimize outcome prediction of a breast screening trial

The ability of pathology characteristics to predict outcome was tested with the 1029 cancers accumulated in the Edinburgh Randomized Trial of breast s creening after 14 years follow-up. The majority (55.7%) were in the screeni ng arm, which also had more operable cases (81.3% vs 62.2%); the reduction in the proportion of inoperable breast cancers in a UK female population in vited to mammographic screening is a notable effect of the trial. In the 69 1 operable invasive cases the size, histological type, grade, node status a nd node number group individually showed highly significant (P < 0.001) ass ociation with survival. In multivariate analysis the Nottingham Prognostic Index (NPI) derived from these features showed highly significant associati on with survival (P < 0.001). However, when first adjusted for NPI, combine d addition of pathological size in 6 categories and histological type as sp ecial or not had an independent association with survival that was statisti cally firmly based (P < 0.001). For operable breast cancer the gains are in smaller sizes, better histological features, and higher proportion node ne gative. The weighting factors applied to pathology indicators of survival i n the NPI are not optimal for a population included in a trial of screening . In particular, a linear trend of the index with pathological size is not appropriate. inclusion of histological type as special or not improves the index further. (C) 2000 Cancer Research Campaign.