Outcome analysis for women undergoing annual versus biennial screening mammography: a review of 24,211 examinations.

OBJECTIVE: Our goal was to determine differences in outcome measures between women undergoing annual versus biennial screening mammography.
MATERIALS AND METHODS: A retrospective review of prospectively collected data on 24,211 consecutive screening mammography examinations was performed in women aged 40-79 years, all of whom had undergone previous normal screening mammography. Annual screening and biennial screening were defined as examinations performed 10-14 months and 22-26 months, respectively, after previous normal screening mammography. The rates of recall, biopsy, cancer detection, and interval cancer for annual and biennial screening cohorts were calculated, as were tumor size, lymph node status, and stage of invasive cancer. Interval cancer cases were identified by linkage with a regional tumor registry.
RESULTS: Of the 4306 biennially screened women, 160 were recalled (3.7%), 45 were biopsied (1.0%), and cancer was detected in 19 (0.44%). Of the 19,905 annually screened women, 518 were recalled (2.6%), 150 were biopsied (0.75%), and cancer was detected in 71 (0.36%). Of the 3278 registry-linked biennially screened women, five had interval cancer (0.15%); of the 15,031 registry-linked annually screened women, 10 had interval cancer (0.07%). For biennial screening-detected cancer and interval invasive cancer combined, the median tumor size was 15 mm, 24% had lymph node metastasis, and 29% were stage 2 or higher. For annual screening-detected cancer, these measures were 11 mm, 14% positive nodes, and 17% stage 2+ cancer, respectively.
CONCLUSION: Annual screening mammography results in lower recall rates than does biennial screening (p < .0001). Moreover, annual screening results in the detection of smaller tumors that have a more favorable prognosis (p = .04).