The association between the pre-diagnosis mammography screening interval and advanced breast cancer.

BACKGROUND

While screening has been demonstrated to reduce breast cancer mortality, the optimal screening interval is unknown. We designed a study to determine the risk of an advanced breast cancer diagnosis by varying the interval between mammograms.

METHODS

We reviewed a single state's mammography records of women diagnosed with breast cancer between 1994 and 2002. The pre-diagnosis screening interval was the number of days between the last two eligible mammograms preceding a cancer diagnosis. The interval was classified as annual (0.75-1.49 years), biennial (1.5-2.49 years) or longer (exceeding 2.49 years). Advanced breast cancer was >or=stage IIB, tumor size >2 cm, or >or=one lymph node with cancer.

RESULTS

The probability of an advanced breast cancer diagnosis did not differ between women with an annual pre-diagnosis screening interval and women with a biennial interval (21.1% vs. 23.7%, P=0.262). A longer pre-diagnosis screening interval was weakly associated with advanced breast cancer (21.8% for intervals 0.75-2.49 years vs. 26.8% for longer intervals, P=0.070). In multivariate analysis, we found an interaction between the pre-diagnosis screening interval and age. Among women 50 years or older, the risk of an advanced breast cancer diagnosis risk was higher for women with a pre-diagnosis screening interval exceeding 2.49 years compared to women with shorter screening intervals (OR 1.99 [1.02-3.90]).

CONCLUSIONS

We found no difference in advanced breast cancer rates between women using mammography annually or biennially. Among women 50 years or older, the advanced breast cancer rate increased when the pre-diagnosis screening interval exceeded 2.49 years.