OBJECTIVE: To determine the frequency of p53 protein accumulation in biopsies of lung cancer patients and to find a correlation between p53 accumulation and patients' age and gender and the differentiation of the tumor. MATERIAL AND METHOD: 201 formalin fixed, paraffin embedded lung tissue sections corresponding to 87 adenocarcinomas, 88 squamous cell carcinomas, 15 large-cell carcinomas, and 11 small-cell carcinomas were retrospectively studied. We have used the labeled streptavidin biotin immunohistochemical method with antibody DO-7, and a microwave pretreatment to recover the antigens. RESULTS: The global frequency of p53 accumulation was 59,7% and the frequency regarding to tumor type was 63,2%, 55,7%, 73,3%, and 45,4%, respectively. CONCLUSION: The protein p53 inversely correlated with the degree of tumor differentiation, but there is no correlation between p53 and patients’ gend...