Prognosis and pathology of screen-detected carcinomas: how different are they?

BACKGROUND: It has been observed that screen-detected breast cancers have a better prognosis than symptomatic tumors, even after taking pathological tumor attributes into account. This has led to the hypothesis that screen-detected tumors are substantially biologically different from symptomatic cancers.
METHODS: The pathology and survival by detection mode was investigated in 21,382 breast cancers diagnosed in women aged 50-64 years in the West Midlands, United Kingdom, between 1988 and 2004. Tumor attributes were compared using chi-square tests and logistic regression. Survival was analyzed using Cox regression.
RESULTS: Screen-detected cancers were significantly smaller, better differentiated, and less likely to be node-positive than symptomatic cancers (P < .001 in all cases). In addition, a higher proportion of screen-detected cancers were hormone receptor-positive, and a higher proportion were tubular carcinomas (P < .001). Survival was substantially better in screen-detected breast cancers (86% at 10 yearsvs 70% for interval cancers and 58% for cancers in women unexposed to screening). Adjustment for age, tumor size, nodal status, grade, histological type, and year of diagnosis accounted for 64% (interval cancers) and 68% (unexposed women) of these survival differences, respectively. Overall survival improved with time. Approximately half of this improvement was due to the increase over time in the proportion of tumors that were screen-detected.
CONCLUSION: The majority of the difference in prognosis between screen-detected and symptomatic breast cancers is due to the differences in routinely measured pathological features (size, type, grade, and nodal status), leaving a small residual difference to be accounted for by other biological differences.