Immunoperoxidase staining for cytokeratins 8 and 18 is very sensitive for detection of occult node metastasis of colorectal cancer: a comparison with genetic analysis of K-ras.

Recent reports suggest that genetic examination of K-ras or p53 mutation is more sensitive for the detection of occult lymph node metastasis in colorectal carcinomas than conventional examination by haematoxylin and eosin (H & E) staining or immunohistochemistry for gene products. The aim of this study was, first, to define the microscopic characteristics of metastatic cancer cells in lymph nodes stained by the anti-cytokeratin antibody CAM5.2 for cytokeratins 8 and 18, and, second, to compare the detection rate of occult lymph node metastasis for immunohistochemical vs genetic methods. K-ras mutations were first examined in primary tumours of seven cases which showed distant metastasis or local recurrence within 5 years of the initial surgery in spite of the original reporting of no lymph node metastasis by routine H & E staining. K-ras mutations were positive in three cases in primary tumours and lymph nodes, and the remaining four primary tumours were negative for p53 mutation as well as K-ras mutation. Therefore, genetic analysis of occult lymph node metastasis was uninformative, but occult metastasis was detected by cytokeratin staining in two of these four cases. Comparative study of cytokeratin-positive cells was performed on each of the 43 lymph nodes from three cases with K-ras mutations. Cancer cells were detected in 28 of the 43 lymph nodes (65.1%) by cytokeratin staining and in 10 of the 43 corresponding lymph nodes (23.3%) by genetic analysis. Artefactual contamination by cancer cells was present in eight of the 28 cytokeratin positive lymph nodes, and three of the eight nodes were genetically positive. This study suggests that cytokeratin immunohistochemistry is more sensitive and specific for the detection of occult lymph node metastasis than genetic diagnosis by K-ras mutation in cases with genetic alterations as well as in cases without them.