Effect of screening mammography on the surgery of breast cancer in Finland: a population-based analysis during the years 1985-2004.

A nationwide mammographic screening of women aged 50 to 59 years commenced in Finland in January 1987. We studied the effect of screening on surgical diagnosis, treatment, and survival of breast cancer in one geographic area in Finland. We reviewed the medical records, survival data from Finnish Cancer Registry, and screening data from the Finnish Mammogrphic Working Group of 1049 women who underwent surgery for breast cancer in our hospital between the years 1985 and 2004. Altogether, 35 parameters including diagnostic procedures, operative data, and staging were recorded. The results of tumors detected by mammographic screening (n=156) and interval cancers (n=148) were compared with the tumors detected outside of screening (n=745). The incidence of breast cancer increased from 35 to 72 cases per 100,000 inhabitants, and the percentage of nonpalpable cancers increased from 12 to 33. Approximately 30 women per 100,000 inhabitants were annually referred from mass screening for surgical biopsies, in 60 per cent of which cancer was detected. Breast lump was still a first sign of cancer in 60 per cent of patients. The mammographic screening detected 20 per cent of new breast cancers. The cancers detected by screening were smaller, found at an earlier stage, and their 10-year-survival was better (90% vs 70%) than those detected by other means (P = 0.003). Overall mortality of interval cancers was worse (27%) than screening cancers (6%, P < 0.0001). Mammographic screening detects up to 20 per cent of new breast cancers in a well-defined population area. The prognosis of screening cancers is better than the cancers found outside of screening.