1. ¹Radiation Therapy Program, BC Cancer Agency, Vancouver Island Centre, 2410 Lee Ave, Victoria, BC, Canada V8R 6V5
2. ²Population and Preventive Oncology Program, BC Cancer Agency, 8th Floor, 686 West Broadway, Vancouver, BC, Canada V5Z 1G1
3. ³Radiation Therapy Program, BC Cancer Agency, Vancouver Centre, 600 West 10th Ave, Vancouver, BC, Canada V5Z 4E6
4. ⁴Screening Mammography Program of BC, 8th Floor, 686 West Broadway, Vancouver, BC, Canada V5Z 1G1

Correspondence: Dr ES Wai, E-mail: ewai@bccancer.bc.ca

Received 16 September 2004; Revised 25 November 2004; Accepted 15 December 2004; Published online 15 February 2005.

Abstract

We compared the long-term impact of 1- and 2-year screening mammography intervals using prognostic, screening, and outcome information for women aged 50–74 years obtained from the Screening Mammography Program of British Columbia in two time periods, prior to 1997 (policy of annual mammography) and after 1997 (biennial mammography). Survival was estimated for both periods using a prognostic model and the expected rate of interval and screen-detected cancers. The likelihood of a screen-detected cancer with annual screening was 2.32 per thousand screens and with biennial screening was 3.32 per thousand screens. The prognostic profile of screen-detected cancers was better than that of interval cancers. Among both screen-detected and interval cancers, the prognostic profiles with annual and biennial screening were similar. The estimated breast cancer-specific survival rates for women undergoing annual and biennial screening mammography were 95.2 and 94.6% at 5 years, and 90.4 and 89.2% at 10 years, respectively. Annual compared to biennial mammography was associated with a 1.2% increase in the estimated 10-year breast cancer-specific survival for women aged 50–74 years, diagnosed with invasive breast cancer after screening programme attendance.