Population studies of the effectiveness of mammographic screening.

OBJECTIVE: To examine population data to see whether survival from breast cancer has improved differentially in screened and unscreened women and examine published studies on mammographic screening to determine whether there is evidence that screening is no longer effective. METHODS: Data was reviewed on trends in breast cancer specific survival among women participating and not participating in the British Columbia Breast Screening Program. Population studies of mammographic screening published between 2000 and 2010 with breast cancer mortality as the outcome were also reviewed. RESULTS: Breast cancer specific survival in British Columbia improved more in screening participants than non-participants, HR=0.74 (0.58,0.93) between the periods 1990-4 and 2000-4. Among the published studies of mortality between 2000 and 2010 selected from different jurisdictions all had found a reduction in breast cancer mortality although this was not always statistically different from zero. Studies had used a range of designs and evaluative methods which may have contributed to the magnitude of the effect reported. CONCLUSION: No evidence was found in the British Columbia data and the published studies reviewed, that treatment or other changes, had caused mammographic screening to become ineffective.