Detection of occult metastases in sentinel lymph nodes from colon cancer patients by K-ras mutation peptide nucleic acid clamp PCR.

Objective: To identify colon cancer patients with occult lymph node metastases.

Background: The prognostic value of regional lymph node (LN) metastases in colorectal cancer patients is well established. The disease recurrences nevertheless experienced by 20% to 30% of the LN negative patients suggest a potential for improvement in current LN diagnostics. We suspect that a subgroup of the patients that are LN negative by routine examination has occult LN metastases that are prognostically relevant.

Methods: To identify these patients we applied ex vivo sentinel lymph node (SLN) mapping to colon cancer patients and analyzed the SLNs by a sensitive peptide nucleic acid clamp PCR (polymerase chain reaction) assay for K-ras mutations, using these mutations as a surrogate marker for tumor cells.

Results: SLNs were identified in 158 (96%) of 164 prospectively recruited patients with localized colon cancer. Of the 158 patients with successful SLN mapping, 67 (42%) had K-ras mutations detected in their primary tumors. We analyzed the SLNs from these patients by peptide nucleic acid clamp PCR for K-ras mutations and found mutations in SLNs from 35 (52%) patients. At least one SLN from 14 (70%) of 20 patients with histologically proven regional LN metastases was positive for the K-ras mutation test. Interestingly, 21 (45%) of the 47 patients without known LN metastases had K-ras mutations detected in their SLNs.

Conclusions: Sensitive detection of K-ras mutations in SLNs from colon cancer patients indicates the presence of occult metastases with potential prognostic implications.