Comparative study of the histopathology of breast cancer in a screened and unscreened population investigated by mammography.

The histopathology of 360 surgical resections for breast cancer in a consecutive series of patients aged 45-69 years from 1979-1983 is described. Two hundred and seventeen patients who were offered screening (screened patients) were compared with 143 patients who were referred as out-patients with breast problems and were not offered screening (unscreened patients). Both groups were investigated by mammography. Comparisons between tumour staging, grading and quadrant involvement are reported. In the screened patients 31% were in the in-situ stage or had an invasive carcinoma less than 1.0 cm in maximum diameter, compared with 7% in the unscreened patients. Conversely 26% of the screened patients had cancers greater than 2.0 cm compared with 52% in the unscreened group. The percentage of cancer patients with lymph node metastases was comparable in both 1.0-2.0 cm and greater than 2.0 cm groups of invasive carcinoma. There were more multiquadrant cancers in the unscreened patients (32%) than screened patients (17%) and this was mainly due to differences in the incidence of carcinomas 1.0-2.0 cm in diameter. This suggests that invasive tumours of comparable size are more likely to produce symptoms leading to detection if multiquadrant. Multicentric cancers were more common in unscreened patients. Differences in the histological grading related to tumour size were found within the screened and unscreened groups but not between the two groups.