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 betwee n woman undergoing annual versus biennial screening mammography. MATERIALS AND METHODS. A retrospective review of prospectively collected da ta on 24,211 consecutive screening mammography examinations was performed i n women aged 40-79 years, all of whom had undergone previous normal screeni ng mammography. Annual screening and biennial screening were defined as exa minations performed 10-14 months and 22-26 months, respectively, after prev ious normal screening mammography. The rates of recall, biopsy, cancer dete ction, and interval cancer for annual and biennial screening cohorts were c alculated, as were tumor size, lymph node status, and stage of invasive can cer. Interval cancer cases were identified by linkage with a regional tumor registry. RESULTS. Of the 4306 biennially screened women, 160 were recalled (3.7%), 4 5 were biopsied (1.0%), and cancer was detected in 19 (0.44%). Of the 19,90 5 annually screened women, 518 were recalled (2.6%), 150 were biopsied (0.7 5%), and cancer was detected in 71 (0.36%). Of the 3278 registry-linked bie nnially screened women, five had interval cancer (0.15%); of the 15,031 reg istry-linked annually screened women, 10 had interval cancer (0.07%). For b iennial screening-detected cancer and interval invasive cancer combined, th e 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 wer e 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 =.0 4).