The effect of mammographic screening on invasive breast cancer in Western Australia

Objective: To determine whether mammographic screening has affected the pre sentation of invasive breast cancer in Western Australia. Design: Population-based reviews of the presentation of all invasive breast cancers diagnosed in Western Australia in 1989 and 1994. Setting: Western Australia (population 1.8 million), Active recruitment of women aged 50-69 years for mammographic screening began in 1989. Main outcome measures: Size and stage of invasive breast cancers at diagnos is. Results: From 1989 to 1994, the age-standardised incidence rose from 109 to 123 per 100 000 woman-years, based on 584 and 750 cases, respectively. The proportion of all invasive breast cancers detected as a result of a mammog ram increased from 9.2% in 1989 to 34.5% in 1994. Among the cases where rel evant information was recorded, the proportion of "impalpable" tumours incr eased from 7.7% in 1989 to 27.6% in 1994, and the average size of palpable tumours fell. There was an unexpected increase in the proportion of tumours that were negative on assays for oestrogen and progesterone receptors. Conclusions: A relatively simple and inexpensive clinical review has booste d confidence that the outlay of public monies required to establish and con duct screening in Australia appears likely to yield the reductions in morta lity from breast cancer that would be predicted on the basis of the earlier controlled trials of mammography.