It has been suggested that a combined analysis of DNA ploidy of the primary tumor and of mediastinal lymph node metastases (LNM) in non-small cell lung cancer (NSCLC) is of prognostic significance in patients with N2-disease, implying that DNA ploidy can contribute towards the selection of patients for operation after a positive mediastinoscopy. To re-evaluate this, DNA flow cytometry was performed in paraffin-embedded material from 117 patients who underwent a complete resection with thorough mediastinal exploration. Flow cytometry was also performed in 54 LNM from 26 patients with N2 disease. The results of flow cytometry were correlated with clinicopathological characteristics and outcome and the data were analysed with the Cox regression model. No correlation was found between DNA ploidy and the survival of 117 patients. The outcome of 10 patients with N2 disease but only diploid LNM was not significantly different compared to that of the 16 patients with N2 disease and aneuploid LNM. When 3 or more LNM were analysed ploidy status was concordant with the ploidy of the primary tumor in 80% of the patients. A pneumonectomy, non-squamous cell carcinoma and N1 and N2 descriptors appeared to be unfavorable prognostic factors in the Cox regression model. It is concluded that combining the results of DNA ploidy in paraffin-embedded tissue from the primary tumor and from the LNM does not discriminate between patients of different prognostic subgroups and therefore most likely will not contribute towards the selection of patients for thoracotomy after a positive mediastinoscopy.

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