OBJECTIVETo investigate micro-metastasis in mediastinal lymph nodes (mLN) of patients with clinical stage I approximately II lung cancer and its clinical significance.

METHODSA total of 181 mLN from 32 lung cancer patients in clinical stage I approximately II were collected during operation and their frozen sections at two different levels were examined immunohistochemically (IHC) with an anti-epithelial cell monoclonal antibody Ber-Ep4. Routine HE staining was done for comparison. The results were processed by Chi-square tests in SPSS 10.0 soft ware.

RESULTSFifteen of the 32 patients (46.9%) were found to have micro-metastasis in 21 of 181 mLN (11.6%) examined by immunohistochemical staining though routine histopathological examinations were negative. Of those 15 cases, micro-metastasis was detected in 9 only by IHC and in 6 both by IHC and HE stainings. The positive rate of micro-metastasis in N0, N1, and N2 stratified by routine pathology was 36.8% (7/19), 33.3% (2/6) and 85.7% (6/7), respectively (N0 vs N2, P < 0.05). When stratified according to clinical staging (cTNM), pathological staging (pTNM) and pathological staging on the basis of IHC (iTNM), the frequencies of N2 cases were 0, 18.8% and 46.9%, respectively (differences among the three groups: P < 0.01). Nine cases reported as N0(7) and N1(2) by routine histopathological examination were found to have micro-metastasis in mLN by IHC staining, therefore they were actually N2 cases.

CONCLUSIONIHC staining with a monoclonal antibody specific for epithelial cells (Ber-Ep4) is more sensitive in the detection of mediastinal micro-metastais than routine HE staining. Underestimation of the extent of mLN metastasis by cTNM and/or pTNM stagings frequently exists in patients with clinically early lung cancer.