Cell‐cycle analysis detecting endogenous nuclear antigens: Comparison with BrdU‐in vivolabeling and an application to lung tumors

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Abstract
The versatility of non‐radioactive cell‐cycle analysis in detecting endogenous nuclear antigens of the proliferating cells was evaluated. Optimal conditions for immunostaining varied in fixation and pretreatment procedures among antigens, bromodeoxyuridine (BrdU), Ki‐67 epitope, DNA polymerase α and PCNA. A significant correlation between BrdU labeling index (LI) was observed in each positive ratio (PR, positive/total neoplastic cells) for nuclear antigens in tumor‐sections which had been labeledin vivowith BrdU. The best correlation was observed in Ki‐67 PR (y = 1.26x+ 2.5;y= Ki‐67 PR;x= BrdU LI;r= 0.97). To determine its prognostic value, Ki‐67 analysis was applied to the surgically resected lung tumors. Ki‐67 PR were different according to the histologic types of the tumors: 47.8 ± 3.4% in small cell carcinoma; 29.5 ± 3.5% in squamous cell carcinoma; 28.3 ± 4.7% in large cell carcinoma; 15.2 ± 1.8% in adenocarcinoma and 0.1 ± 0.1% in mature carcinoid tumor. When the mean value was used to divide each type to a higher or lower proliferative activity (15% Ki‐67 PR for adenocarcinoma and 30% for squamous cell carcinoma), the group with the lower Ki‐67 PR showed a significantly more favorable prognosis than that of a higher ratio. Ki‐67 PR was not correlated with other pathologic factors such as size, lymph node metastasis or pleural involvement. Non‐radioactive cell‐cycle analysis was feasible and useful for detecting endogenous nuclear antigens even in the lung tumors, particularly when the analysis was coupled with histologic typing.