ABSTRACT
PURPOSE: To determine the frequency of BI-RADS category 3 nonpalpable masses detected using only sonography (US) and the malignancy rate among these lesions. Second, to validate a proposed short-term follow-up regimen based on long-term observational results. METHODS: This prospective cohort study was conducted between September 2003 and April 2010. We conducted a 2-year short-term follow-up protocol composed of five US examinations at 3-month intervals for the first 6 months, and at 6-month intervals for the next 18 months, followed with age-appropriate screenings. Biopsy was recommended for the masses increasing in size and with changing imaging features. RESULTS: The frequency of category 3 nonpalpable masses detected only on US in 11,373 consecutive women was 5.3%. Of 562 lesions found in 451 women, 394 (70.1%) remained stable during the short-term and subsequent follow-up. Seventy-four (13.1%) masses showed interval regression and 79 (14.0%) showed interval progression. The malignancy rate was 0.3% (2 of 562), with about 85% of interval changes occurring within the first 2 years. The negative predictive value of US in the detection of cancer was 99.6% (95% CI, 98.7-99.9). The mean follow-up time was 65.5 ± 8.7 months. CONCLUSIONS: The frequency of BI-RADS 3 nonpalpable masses detected using sonography alone was 5.3%. During follow-up, the majority of interval changes occurred within the first 2 years. Because these masses have a very low malignancy rate, a 2-year follow-up instead of immediate biopsy is an appropriate option.
