False-positive and false-negative sentinel node findings in 473 breast cancers.

We reviewed lymph node samples from 473 consecutive breast cancer cases with either negative sentinel nodes or isolated tumor cells to evaluate the rate of false-positive sentinel node findings. Nuclear morphometry was applied to compare nuclear atypia between the primary tumor and metastases classified as isolated tumor cells by size. In addition, the role of the diagnostic preoperative biopsy method, either core needle biopsy or fine needle aspiration cytology, on the prevalence of isolated tumor cells was investigated. In addition, we studied the expression of metastasis-associated protein 1 in the primary tumor and corresponding metastases in 95 cases, including 52 isolated tumor cell cases, to distinguish a true metastasis from a benign epithelial displacement. Our review revealed 4 false positives and 7 false negatives from 473 sentinel node cases. In addition, 5 true-positive cases were upstaged from isolated tumor cells to micrometastases. No association was found between the preoperative biopsy method and the sentinel node status (P=.859). There was no difference in nuclear atypia, when the cells in isolated tumor cells and primary tumor were compared. Therefore, small metastases do not represent benign epithelial displacement. Isolated tumor cell findings did not correlate with preoperative biopsy methods. The metastasis-associated protein 1 staining score sum was lower in the metastases than in the primary tumor in 72% of cases, including all sizes of metastases. These data suggest that metastasis-associated protein 1 staining is not ideal for investigating the possible malignant nature of smaller metastases because of the relatively low concordance between the primary tumor and metastases, even macrometastases.