AIMS--To investigate the immunohistochemical expression of p53 protein in small cell lung carcinoma (SCLC), comparing it with that in non-small cell carcinoma (NSCLC); and to evaluate the correlation between p53 and proliferating cell nuclear antigen (PCNA) expression as well as between p53 and PCNA expression and survival. METHODS--Paraffin wax embedded tissues from 61 cases of primary lung carcinoma were stained for p53 protein and PCNA using the monoclonal antibodies 1801 and PC-10, respectively, in a standard avidin-biotin immunoperoxidase method. RESULTS--Of the 61 lung carcinomas 35 (57%) were positive for p53 (range 1% to 90%). Ninety percent of the non-oat SCLC contained positive cells and the labelling index (LI) was significantly higher than that of the oat SCLC (p < 0.001). SLCC also displayed a higher p53 LI than NSCLC (p < 0.01); no difference was found between squamous carcinoma, adenocarcinoma, and oat cell carcinoma. A p53 LI of greater than 1% tended to be associated with nodal metastases (p < 0.05), and p53 expression in node positive tumours as well as in oat cell carcinomas was indicative of poorer survival (p < 0.01 and p < 0.1, respectively). A p53 Li of greater than 60% was a negative prognostic factor in non-oat SCLC (p < 0.05). PCNA LI was highest in non-oat SCLC and lowest in NSCLC; oat cell carcinomas had a mean LI intermediate between NSCLC and non-oat SCLC (NSCLC v oat cell carcinoma p < 0.05 and oat cell v non-oat cell carcinomas p < 0.01). A PCNA LI was not correlated with nodal metastases or survival, but there was a significant positive correlation between PCNA LI and p53 LI (rs = 0.484, p < 0.001). CONCLUSIONS--p53 and PCNA expression differ substantially among the various types of lung carcinomas. Substantial differences were also found between oat and non-oat types of SCLC, indicating that SCLC is heterogeneous as far as proliferation rate and altered p53 expression is concerned. p53 seems to be of some prognostic value. The relation between PCNA and p53 expression indicates that the PCNA gene is slightly upregulated by p53.
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