Background: A trend toward earlier breast carcinoma detection in the United States has been attributed to screening mammography, although direct evidence linking this trend to the increased use of mammography in a general population is lacking. This study examined the effects of mammography on tumor size and axillary lymph node metastasis in Vermont over 25 years.
Methods: Pathology and mammography data from 3499 Vermont women who were diagnosed with invasive breast carcinoma during 1975-1984, 1989-1990, and 1995-1999 were compared. Logistic regression analysis was used to estimate the effects of age, mammography use, and period on the odds of a tumor < or = 2 cm and the odds of negative lymph nodes.
Results: The proportion of breast tumors that were detected by screening mammography increased from 2% during 1974-1984 to 36% during 1995-1999 (P < 0.001), and these tumors were more likely to measure < or = 2 cm than tumors that were detected by other methods. Among women age > 50 years, the odds ratio (OR) was 4.5, with a 95% confidence interval (95% CI) of 3.5-6.4. The effect was smaller in younger women (OR, 1.8; 95% CI, 1.1-3.0). Mammographic detection increased the odds of negative lymph nodes by a similar amount in both age groups, although women age > 50 years were more likely to have negative lymph nodes than younger women (OR, 1.3; 95% CI, 1.1-1.6). Tumor size and lymph node metastasis also were related to the number of mammograms and to the mammographic interval.
Conclusions: Most of the trend toward earlier detection in Vermont was due to mammography. Mammography had a lesser effect on tumor size among younger women, which may be related to less frequent screening, although its effect on lymph node metastasis was not age dependent. Women age < 50 years were more likely to have positive lymph nodes, independent of the method of detection or the frequency of mammography.
Copyright 2002 American Cancer Society.