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

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). 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. 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). 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.