The p53 gene is a tumor suppressor gene which is located on band 13p of chromosome 17. It encodes a 53-kd nuclear phosphoprotein, and has been found in all mammalian cells. It is thought to play a role in the control of the cell cycle. The wild type p53 protein inhibits cell proliferation by arresting cells in the G1 phase of the cell cycle, and loss of this activity can lead to neoplastic transformation.1-3 Mutations in p53 gene are the most common genetic alterations in several human malignancies, including lung, breast, colorectal, ovarian and cutaneous neoplasms, although the prognostic value of altered p53 expression is still debated. [4][5][6] Under physiological conditions, the wild type protein has a short half-life to allow immunohistochemical detection.7 However, the mutant type is more stable than the wild type, and is detectable in cell nuclei by standard immunohistochemical staining procedures. 1,7 To investigate the role of p53 in cell proliferation, we focused on markers of the cell cycle whose expression could be correlated with p53 immunohistochemical detection. One such marker is the proliferating cell nuclear antigen (PCNA). PCNA is a 36-kd nuclear polypeptide that is related to cell proliferation. PCNA, an auxilliary protein for DNA polymerase, is identical to cyclin, synthesized during the late G1 to S phase. The synthesis of PCNA is reported to be directly correlated with DNA replication and cell proliferation. 8,9 Our hypothesis was that p53 overexpression may be associated with increased cell proliferation, which might affect the clinical outcome of non-small cell lung carcinomas (NSCLC) and small cell lung carcinomas (SCLC). We examined the expression of p53 and PCNA immunohistochemically. The aim of this study was to evaluate the relationship of p53 and age, sex, nodal involvement, tumor stage, tumor size and proliferative activity in NSCLC and SCLC. Materials and MethodsThis study was based on 60 cases of primary lung carcinoma taken from the files of the Pathology Department, School of Medicine, Akdeniz University. Tumor tissue was obtained by biopsy (n=22, SCLC) or surgical resection (n=30, NSCLC and n=8, SCLC). The pathologic features of the surgical specimens were classified and staged according to the World Health Organization criteria and TNM staging system. Cases of NSCLS consisting of 24 squamous, 1 adenosquamous and 5 adenocarcinomas were examined. In the resection specimens, the size of the tumor and the tumor stage, vessel and nerve invasion, lymph node and pleura involvement were evaluated.All specimens were fixed in 10% formalin and routinely processed for paraffin wax embedding. Sections were cut into 5 μ pieces, mounted on glass and dried overnight at 37°C. All sections were then deparaffinized in xylene, rehydrated through alcohol and washed in phosphate-buffered saline. This buffer was used for all subsequent washes and for dilution of the antibodies. Sections for p53 detection were heated in a microwave oven twice for 5 minutes at 700 W in citrate buffer (pH: 6). Mono...