Research article
Improved breast cancer survival following introduction of an organized mammography screening program among both screened and unscreened women: a population-based cohort study
-
* Corresponding author: Mette Kalager mette.kalager@kreftregisteret.no
1 The Cancer Registry of Norway, P.O.B 5313 Majorstuen, N-0304 Oslo, Norway
2 Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, P.O.B 281, SE-17 177 Stockholm, Sweden
3 Department of Epidemiology, Harvard School of Public Health, 677 Huntington Avenue, Boston, MA 02115, USA
Breast Cancer Research 2009, 11:R44 doi:10.1186/bcr2331
Published: 6 July 2009Abstract
Introduction
Mammography screening reduces breast cancer mortality through earlier diagnosis but may convey further benefit if screening is associated with optimized treatment through multidisciplinary medical care. In Norway, a national mammography screening program was introduced among women aged 50 to 69 years during 1995/6 to 2004. Also during this time, multidisciplinary breast cancer care units were implemented.
Methods
We constructed three cohorts of breast cancer patients: 1) the pre-program group comprising women diagnosed and treated before mammography screening began in their county of residence, 2) the post-program group comprising women diagnosed and treated through multidisciplinary breast cancer care units in their county but before they had been invited to mammography screening; and 3) the screening group comprising women diagnosed and treated after invitation to screening. We calculated Kaplan-Meier plots and multivariable Cox proportional hazard models.
Results
We studied 41,833 women with breast cancer. The nine-year breast cancer-specific survival rate was 0.66 (95%CI: 0.65 to 0.67) in the pre-program group; 0.72 (95%CI: 0.70 to 0.74) in the post-program group; and 0.84 (95%CI: 0.80 to 0.88) in the screening group. In multivariable analyses, the risk of death from breast cancer was 14% lower in the post-program group than in the pre-program group (hazard ratio 0.86; (95%CI: 0.78 to 0.95, P = 0.003)).
Conclusions
After nine years follow-up, at least 33% of the improved survival is attributable to improved breast cancer management through multidisciplinary medical care.