INVASIVE INTERVAL CANCERS IN THE OSTERGOTLAND MAMMOGRAPHIC SCREENING-PROGRAM - RADIOLOGICAL ANALYSIS

The aim of this study was to find out by radiological analysis whether it is possible to prevent interval cancers in screening programmes wi thout a concomitant increase in false positives. Re-scrutiny of all ma mmograms of 544 interval cancers was implemented. Blinded re-scrutiny of screening mammograms of 390 interval cancers mixed with other cases (prevalence of detectable cases 37%) by two outside radiologists was also carried out. True interval cancers constituted 49%, missed tumour s 25%, occult tumours 10% and unclassifiable cases 16%. There were no significant differences in survival between true interval cancers, ove rlooked or misinterpreted cancers, and mammographically occult cancers . In the blinded re-scrutiny both examiners reached a positive predict ive value for malignancy of 67%, and a sensitivity of 69% and 81%, res pectively. In a screening programme such as this, it was estimated tha t 100-400 additional women would have to be recalled from screening fo r further workup in order to detect each additional cancer which would otherwise emerge as an interval cancer. The occurrence of interval ca ncer increased with age and was influenced by the design of screening. The proportion of patients with potential iatrogenic delay in diagnos is (overlooked and misinterpreted cancers) was equivalent to figures f rom other studies. There were no significant differences in survival b etween the various categories of interval cancer. The study confirmed the association of criteria for referral for further investigation wit h the number of false positives. Efforts to reduce the number of inter val cancers by lowering the threshold for recall are likely to be coun terproductive.