Colorectal carcinoma nodal staging. Frequency and nature of cytokeratin-positive cells in sentinel and nonsentinel lymph nodes.

CONTEXT: Nodal staging accuracy is important for prognosis and selection of patients for chemotherapy. Sentinel lymph node (SLN) mapping improves staging accuracy in breast cancer and melanoma and is being investigated for colorectal carcinoma.
OBJECTIVE: To assess pathologic aspects of SLN staging for colon cancer.
DESIGN: Sentinel lymph nodes were identified with a dual surgeon-pathologist technique in 51 colorectal carcinomas and 12 adenomas. The frequency of cytokeratin (CK)-positive cells in mesenteric lymph nodes, both SLN and non-SLN, was determined along with their immunohistochemical characteristics.
RESULTS: The median number of SLNs was 3; the median number of total nodes was 14. The CK-positive cell clusters were detected in the SLNs of 10 (29%) of 34 SLN-negative patients. Adjusted per patient, SLNs were significantly more likely to contain CK-positive cells than non-SLNs (P <.001). Cell clusters, cytologic atypia, and/or coexpression of tumor and epithelial markers p53 and E-cadherin were supportive of carcinoma cells. Single CK-positive cells only, however, could not be definitively characterized as isolated tumor cells; these cells generally lacked malignant cytologic features and coexpression of tumor and epithelial markers and in 2 cases represented mesothelial cells with calretinin immunoreactivity. Colorectal adenomas were associated with a rare SLN CK-positive cell in 1 (8%) of 12 cases.
CONCLUSIONS: Sentinel lymph node staging with CK-immunohistochemical analysis for colorectal carcinomas is highly sensitive for detection of nodal tumor cells. Cohesive cell clusters can be reliably reported as isolated tumor cells. Single CK-positive cells should be interpreted with caution, because they may occasionally represent benign epithelial or mesothelial cells.