Objective: Detection of disseminated tumor cells in mediastinoscopic biopsies could improve staging and might be helpful concerning indications for neoadjuvant therapy regimens. This prospective study was performed to evaluate a simple and observer-independent polymerase chain reaction (PCR)-based method for the detection of disseminated tumor cells in regional lymph nodes.
Methods: Lymph nodes of 32 consecutive patients without neoadjuvant therapy were removed by systematic lymphadenectomy during resection of primary NSCLC. One hundred of these lymph nodes were cut into two equal halves which were examined using either routine histopathology or quantitative reverse transcriptase PCR (qRT-PCR). qRT-PCR amplification of cytokeratin 19 (CK19) transcripts was applied for the detection of tumor cell-specific RNA. We differentiated between illegitimate marker gene transcription and cancer-specific expression by using a cut-off value that was obtained from the analysis of 18 lymph nodes of patients with benign lung diseases. Subsequent to the evaluation of qRT-PCR, a pilot project with five additional patients was conducted to examine 19 mediastinoscopic biopsies, which were cut into two equal halves and proceeded as described above.
Results: Ninety-four (94%) lymph nodes were tumor-free by histopathology. qRT-PCR detected disseminated tumor cells in 26 (28%) of these lymph nodes. All of the remaining six lymph nodes that were judged by the pathologist to contain tumor cells exhibited CK19 transcripts. Twenty-three patients had a pN0 status. qRT-PCR detected disseminated tumor cells in 13 (56%) of these pN0 patients. The mediastinoscopic biopsies showed disseminated tumor cells in four (21%) out of 19 histopathologically tumor-free samples.
Conclusions: CK19 qRT-PCR is a sensitive and specific tools for the detection of disseminated tumor cells in regional lymph nodes of patients with operable NSCLC. Further studies are required to asses if this molecular method might improve mediastinoscopic staging.