Identification of occult tumor cells in node negative lymph nodes of colorectal cancer patients by cytokeratin 20 gene and protein expression.

BACKGROUND AND AIMS: Evaluation of cytokeratin 20 (CK20) specific quantitative reverse transcriptase polymerase chain reaction (QRT-PCR) and immunohistochemistry (IHC) for detection of occult tumor cells in lymph nodes of 72 patients with colorectal carcinoma (UICC stage I and II).
METHODS: Serial sections of formalin-fixed, paraffin-embedded lymph nodes (mean 14.3/case) were used for microdissection, RNA isolation and QRT-PCR and for CK20 IHC using routine protocols. Results of QRT-PCR and IHC were compared and correlated to the CK20 expression pattern of the primary tumors and clinical follow-up.
RESULTS: IHC revealed CK20-positive tumor cells in lymph nodes of 14.5% (10/69) and 0% (0/3) cases with a CK20-positive and CK20-negative primary tumor, respectively. CK20 mRNA was detected in the lymph nodes of 36.8% (7/19) cases by QRT-PCR with all 7 cases also expressing CK20 mRNA in the primary tumor. CK20 mRNA (QRT-PCR) and protein (IHC) detection in serial sections did not agree in 25% (5/20) of cases. A trend was seen towards a worse disease course for patients with CK20-positive lymph nodes by IHC (incidence of recurrent disease) and QRT-PCR (disease-free survival, incidence of recurrent disease).
CONCLUSION: CK20-specific IHC and QRT-PCR are supportive tools to conventional histology for detection of occult tumor cells in archival tissues, with the restriction that a laborious QRT-PCR procedure is necessary to achieve appropriate specificity. A prognostic value of CK20 IHC or QRT-PCR for stratification of UICC stage I and II patients into those likely to develop recurrent disease was not evident.