[Incidence of breast cancer before and after implementation of mammography screening]

A nationwide governmentally founded breast cancer screening program for women aged 50 - 69 years was gradually implemented in all Norwegian counties between November 1995 and February 2004 (the Norwegian Breast Cancer Screening Program, NBCSP). Such an implementation is expected to give an initial increased incidence followed by a decrease. We here present general and stage-specific incidences of breast cancer by age groups, in the first 9 counties that implemented the NBCSP.

The incidence of invasive breast cancer is shown for the counties Akershus, Hordaland, Oslo and Rogaland (AHOR), and Agder (east and west), Telemark, Troms and Finnmark (AgTmTF) for the period 1990-2003. AHOR started the NBCSP in 1995/1996, and AgTmTF started in 1999/2000. The incidence is based on recordings in the main database at the Cancer Registry, and is shown in rates per 100,000 women years.

The incidence of breast cancer in women aged 50-69 years increased from 200 to 350 per 100,000 women years at start-up of the NBCSP and subsequently decreased to approximately 250. Before starting the program, the incidence was higher in women aged 70-74 years than in those aged 50 - 69. This changed in the subsequent period. During 1990-2003, the incidence of breast cancer was stable in women aged 20-49 and in those older than 74 years. At start-up of the NBCSP, a higher proportion of breast cancers in Stadium I were diagnosed as compared to the period before, especially among women aged 50-69 years.

Introduction of the NBCSP has changed the incidence of breast cancer in women aged 50-69 and in those aged 70-74 years.