Objective: The purpose of our study was to determine if annual mammographic screening was superior to biennial screening in women more than 64 years old by examining differences in various prognostic indicators.
Materials and methods: We reviewed the records of 119 consecutive women 65 years old and older with 120 cases of breast cancer who had a previous normal screening evaluation for breast cancer that included mammography and physical examination 8-30 months before diagnosis. A search of the computerized tumor registry, clinical records, and breast imaging records from November 1988 to April 1995 provided our cases. Screening intervals were defined as 6-18 months (annual) and 19-30 months (biennial). Mammographic, histologic, and clinical features were reviewed. Disease severity (DS) levels were assigned to each tumor as follows: DS-1 included minimal disease (ductal carcinoma in situ [TisNO], T1aN0, and T1bN0 tumors), DS-2 included all T1cN0 tumors, DS-3 included tumors larger than 2 cm in diameter with lymph nodes that were negative for cancer, and DS-4 included all metastatic disease. Statistically significant differences were calculated using the Wilcoxon rank sum test, Fisher's exact test, and the chi-square test.
Results: Ninety-three tumors were found in the group of patients who were annually screened, and 27 were found in the group of patients who were screened biennially. The women who underwent yearly screening mammography had significantly smaller invasive tumors (average, 10.7 mm; median, 9.5 mm versus 16.5 mm and 15.0 mm, respectively; p = .0086). The women who were screened annually also had significantly less advanced disease than women screened biennially (annually screened patients versus biennially screened patients: DS-1, 72% versus 44%; DS-2, 23% versus 37%; DS-3, 2% versus 11%; DS-4, 3% versus 7%; p = .0071). The group of patients screened annually had fewer cases of lymph node metastases (3% versus 8%; p = .12) and three times as many cases of ductal carcinoma in situ (22% versus 7%, p = .10).
Conclusion: Annual screening mammography revealed significantly smaller tumors and less advanced cases of cancer than biennial screening, providing inferential support for annual mammographic screening of women more than 64 years old.