Factors influencing accuracy of axillary sentinel lymph node frozen section for breast cancer

Background: Intraoperative sentinel lymph node (SLN) frozen section (FS) guides immediate axillary lymph node dissection in breast cancer patients. Methods: The Oregon Health & Science University pathology database was searched for SLN FS From October 1999 to January 1, 2009. Slides of positive cases were reviewed and metastasis sizes measured. Results: Of 416 cases, 129 were positive (31%) on permanent sections and immunohistochemistry, with 79 concordant and 50 false-negative FS. Accuracy was 88%, sensitivity 61%, and specificity 100%. FS accuracy for lobular carcinoma (76%) was lower than for invasive ductal carcinoma (88%) (P = .048). FS accuracy significantly differed by size of nodal tumor. For 49 cases of tumor ≤ 2 mm (isolated tumor cells plus micrometastases), the accuracy of FS was 18%; for 77 cases of >2-mm metastases, accuracy was 90% (P < .0001). Conclusions: False-negative FS were predominantly small nodal tumor deposits not sampled at FS. Although accuracy was lower, SLN FS is still beneficial in lobular carcinoma, but not ductal carcinoma in situ.