Sentinel lymph node mapping: detection of micrometastases by polymerase chain reaction in non-small cell lung cancer

OBJECTIVE We applied a new protocol, which includes polymerase chain reaction (PCR) for RNA detection of cytokeratin 7 and 19, to all the SLNs, to detect micrometastases and to define an improvement of staging. METHODS Since January 2005, we have applied the SLN technique to 22 patients. The peri-lesional injection of 99mTc-nanocolloid suspension was performed under computed tomographic guidance (seven cases), with fiberoptic broncoscopy (five cases), with thoracoscopy (two cases), and after thoracotomy (eight cases). In three cases, the intraoperative pathological evaluation identified a benign lesion; therefore the RT-PCR molecular staging technique was not applied. In the other cases, resection with mediastinal lymph node dissection was performed. The SLN was divided into two parts: one was frozen for PCR study, the other was fixed and paraffin-embedded for IHC. RESULTS We identified SLNs in 16 patients with NSCLC (85%). In three patients, we were unable to identify the SLN, probably because the 99mTc-nanocolloid suspension had been injected within the tumor and not at the edges, and migration had been impaired by the peritumoral fibrous-inflammatory reaction. Routine pathology evaluation showed stage I disease in 13 patients, T3N0 in one patient, and N2 disease in five patients. In seven patients, IHC identified lymph node metastasis (two cases resulted in N0 according to routine pathology). RT-PCR analysis was performed in 10 patients: in six patients, micrometastases were identified (three resulted in N0 according to routine pathology; one remained N0 even after IHC evaluation). Three micrometastatic NSCLC were therefore identified. The skip-metastasis phenomenon was not observed in this series. Three patients with N2 disease relapsed. One patient with N0 disease per classic pathology and IHC but with RT-PCR identification of micrometastases experienced systemic relapse 3 months after surgery. CONCLUSIONS The SLN technique was able to provide a subgroup of patients for whom the use of expensive molecular procedures, such as RT-PCR, could be applied on a well-focused target (the SLN). This approach could improve the accuracy of pathologic staging in identifying a subset of patients with a higher risk of relapse.