Stereotactic 9-gauge vacuum-assisted breast biopsy, how many specimens are needed?

To determine the minimum number of stereotactic 9-gauge vacuum-assisted biopsy specimens required to establish a final histopathological biopsy diagnosis of mammographically suspicious breast lesions.

This prospective single-center observational cohort study included 120 women referred for stereotactic vacuum-assisted biopsy of 129 mammographically suspicious lesions between December 2017 and October 2018. Stereotactic 9-gauge vacuum-assisted biopsy was performed, acquiring twelve specimens per lesion. Calcification retrieval was assessed with individual specimen radiography. Each specimen was histologically analyzed in chronological order and findings were compared with the final histopathological result after assessment of all twelve specimens and with results of surgical excision. Cumulative diagnostic yield per specimen was calculated.

In total, 131 biopsy procedures were performed in 120 women (mean age 59 years). In 95% (95%CI 90%-98%) of the procedures a final histopathological diagnosis was reached after six specimens. After nine specimens the final biopsy diagnosis was established in all 131 cases. In the subgroup of 41 patients with a DCIS or invasive diagnosis at biopsy there were eight procedures (20%) where calcifications were retrieved before the diagnostic specimen was obtained. Underestimation of subsequent resection diagnosis occurred in six out of 30 excised lesions classified as DCIS (20%) and in one out of four excised high-risk lesions.

With six stereotactic 9-gauge vacuum-assisted biopsy specimens a final histopathological biopsy diagnosis could be established in 95% (95%CI 90%-98%) of the biopsy procedures. Taking nine 9-gauge specimens seems to be optimal. Ending the stereotactic vacuum-assisted breast biopsy procedure as soon as calcifications are retrieved may cause false negative results.