Molecular detection of neoplastic cells in lymph nodes of metastatic colorectal cancer patients predicts recurrence

Disseminated disease, especially to the liver, constitutes the major risk o f recurrence for colorectal cancer patients. However, successful resection can still be achieved in 25-35% of colorectal cancer patients with isolated metastases, To evaluate the clinical value of occult micrometastatic disea se detection in lymph nodes, we tested genetic (K-ras and p53 gene mutation s) and epigenetic (p16 promoter hypermethylation) molecular markers in the perihepatic lymph nodes from colorectal cancer patients with isolated liver metastases, DNA was extracted from 21 paraffin-embedded liver metastases a nd 80 lymph nodes from 21 colorectal cancer patients. K-ras and p53 gene mu tations were identified in DNA from liver metastases by PCR amplification f ollowed by cycle sequencing. A sensitive oligonucleotide-mediated mismatch ligation assay was used to search for the presence of K-ras and p53 mutatio ns to detect occult disease in 68 lymph nodes from tumors positive for thes e gene mutations. Promoter hypermethylation at the pld tumor suppressor gen e was examined in both liver lesions and lymph nodes by methylation-specifi c PCR, Sixteen of the 21 (76%) liver metastases harbored either gene point mutations or p16 promoter hypermethylation, Twelve of the 68 lymph nodes we re positive for tumor cells by molecular evaluation and negative for tumor cells by histopathology and cytokeratin immunohistochemistry, whereas none were positive for tumor cells by histopathology or negative for tumor cells by molecular analysis (P = 0.0005, McNemar's test). Moreover, in three pat ients with lymph nodes that were histologically negative at all sites, mole cular screening detected tumor DNA at one or more lymph nodes. Survival ana lysis shelved a median survival of 1056 days for patients without evidence of lymph node involvement by molecular analysis and 165 days for patients w ith positive lymph nodes by this approach (P = 0.0005), These results indic ate that lymph node metastasis screening in colorectal cancer patients by m olecular-based techniques increases the sensitivity of tumor cell detection and can be a good predictor of recurrence in colorectal cancer patients wi th resectable liver metastases.