In
head and neck squamous cell carcinomas (
HNSCC),
metastasis to cervical lymph nodes is a major determinant of patient outcome. To detect
metastases, we used the MET oncogene as marker, which encodes the receptor for
hepatocyte growth factor/
scatter factor, mediating epithelial cell motility and invasiveness. The MET gene is expressed in epithelia and over-expressed in
carcinomas of specific histotypes, but not in lymphatic tissue. A total of 151 lymph nodes from 20
squamous cell carcinomas were studied with both in-depth histology and end-point and real-time quantitative RT-PCR. MET-encoded sequences were found in 61 of 151 nodes (40%), of which 24 (16%) were found metastatic by in-depth histopathology. Parallel routine histopathologic analysis of 654 lymph nodes from the same cases identified 36
metastases (5%). Real-time quantitative RT-PCR was used to measure MET gene-specific
mRNA in normal tissues, primary
tumors and
lymphatic metastases and showed a 2-8-fold increased expression in
tumor cells which metastasize. RT-PCR for 3 cytokeratins expressed in
HNSCC (K4, K10 and K13) proved to be less sensitive in detecting occult
lymphatic metastases. Western blot analysis demonstrated the presence of the full-size MET receptor in primary
tumors and
lymph node metastases; immunohistochemistry showed receptor localization in
tumor cells. Altogether, these data demonstrate that the MET gene product is a valuable marker with which to detect occult
tumor cells in lymph nodes, thanks to its high expression in metastatic cells. After RT-PCR analysis we were able to attribute a more advanced stage to 10 out of 20
HNSCC cases, including 5 cases classified as
tumor-free after routine histopathology.