Breast cancer in NSW women: a shift in tumour size

To determine whether there has been an increase in the proportion of small (< 1 cm in size) and localised breast cancers in women aged 50-69 (the group actively recruited to mammographic screening) compared with women aged 40-49.

Cases of invasive breast cancer in women aged 40-69 notified to the NSW Central Cancer Registry in 1986, 1989 and 1992 were included. Tumour sizes were determined from histopathology reports.

A higher percentage of breast cancers were under 1 cm in size in 1992 (10%) than in 1986 and 1989 (7%). The increase in the percentage of small breast cancers was statistically significant in women aged 50-69 (chi 2 for linear trend, 7.9; P = 0.005) but not in those aged 40-49 (chi 2 for linear trend, 2.5; P = 0.12). Slightly more than half the breast cancers (53%) in 1992 were localised to the breast, representing an increase from 49% in both 1986 and 1989. This increase was also statistically significant in women aged 50-69 (chi 2 for linear trend, 3.9; P = 0.05) but not in those aged 40-49 (chi 2 for linear trend, 1.4; P = 0.24).

Breast cancers in 1986, 1989 and 1992 showed a moderately strong shift to smaller tumours and localised disease in women aged 50-69. As women of this age group were targeted by mammographic screening, the widespread availability of mammography may explain this shift.