US follow-up protocol in concordant benign result after US-guided 14-gauge core needle breast biopsy.

To determine the time when follow-up ultrasound (US) should begin for concordant benign lesions after US-guided 14-gauge core needle breast biopsy (CNB). This was an IRB-approved retrospective study, with a waiver of informed consent. Among 3,888 consecutive US-guided CNBs performed between August 2005 and March 2008, 1,492 breast masses in 1,309 women with concordant benign results and follow-up US after CNB were included. Their medical records were reviewed. Statistical comparisons for the result of first follow-up US and malignant rates among 6-month, 12-month, and long-term intervals were performed by using Fisher exact test. Results dichotomized for symptom, lesion size (10 mm), and CNB result (specific or not), were also analyzed. In 1,492 masses, seven malignancies (0.5%) were diagnosed by interval growth at first follow-up US performed at 6-month (n = 3), 12-month (n = 1), and long-term interval (n = 3). No significant difference in results of follow-up US and malignant rates was found among follow-up intervals. At 6-month interval, malignant rate in symptomatic group (1.9%, 3/162) was significantly higher than in asymptomatic group (0%, 0/819) (P = 0.004). The size of malignancy at long-term interval tended to be larger than at shorter interval, and metastasis was developed in one patient with malignancy at long-term interval. Concordant benign lesions after US-guided 14-gauge CNB should be recommended to begin US follow-up at least at 12 months to detect early-stage cancers. However, for concordant benign lesion associated with any clinical symptoms, follow-up US should begin earlier, at 6 months after CNB.