Pathology results from the UK Age Trial

The UK Age Trial was initiated in 1991 to address the question of whether annual mammography from age 40 years reduces mortality from breast cancer and by what percentage. At present, only surrogate end points generated by pathology review of cancers can be used for a preliminary estimate of mortality/survival benefit for the study arm. All cases of breast cancer in the appropriate age range were systematically identified and relevant material retrieved for centralised, blinded review by a panel of three pathologists following classification principles outlined in the UK Guidelines. The total number of cancers identified in the Trial population up to 31 December 1999 was 1288.

There was a high proportion of special types in incidence and interval cancers but the explanation in each set differs; for incidence cases the preponderance is for tubular cancers, while for interval cases it is lobular cancers. For grade, incidence screens yielded the highest proportion of grade I and a low grade III, whereas interval cancers showed the converse, with low grade I and high grade III proportions. For node status, the highest negative proportion was found for incidence screens and the lowest was seen in 'never attended' cases. These features provide clear confirmation of the length bias influence anticipated for the screened subpopulations, but they are not fully informative for screening effects or for understanding cancer natural history.