Human non-small cell lung cancer: p53 protein accumulation is an early event and persists during metastatic progression

Molecular pathology of non-small-cell lung cancer

The molecular basis of lung carcinogenesis must be understood more fully and exploited to enhance survival rates of patients suffering from lung cancer. In this review we will discuss the major molecular alterations that occur in lung cancer. Emphasis is placed on alterations that occur early during carcinogenesis since they might be relevant for future screening programs. Finally we will shortly review new approaches that are used to study the molecular pathology of lung cancer and how they can be applied in a clinical setting.

Suprabasal p53 immunostaining in premalignant endobronchial lesions in combination with histology is associated with bronchial cancer

Endobronchial carcinoma develops through a continuum of morphologically recognizable pre-neoplastic changes. At present, no marker has been identified that can reliably predict the biological behavior of these lesions. Endobronchial lesions (n=39) sampled from patients (n=20) without clinically overt lung cancer, were analyzed by immunohistochemistry (IHC) for abnormal expression regarding the p53 protein, i.e. suprabasal p53 expression. Clear suprabasal p53 immunostaining was found in two (12%) of the hyperplastic or squamous metaplastic lesions, in one (10%) of the mildly or moderately dysplastic lesions and in nine (75%) of the severely dysplastic or carcinoma in situ (CIS) lesions. Suprabasal p53 immunostaining was found significantly more frequent in severe dysplasia or CIS (P<0.01). Of 17 patients follow-up data were available. After a median follow up of 7 months (range 2-37 months), six patients presented with bronchial carcinoma within the same lobe or bronchial spur where biopsies had been taken. Four of these patients revealed suprabasal p53 immunostaining in the biopsies obtained from the sites of future cancer. In three patients biopsies were obtained from future cancer sites as well as from distant sites in the ipsilateral lung. Suprabasal p53 immunostaining was found exclusively at future cancer sites of these patients (P=0.02). Suprabasal p53 immunostaining in addition to histology improved the specificity and the positive predictive value for bronchial carcinoma development in the same lobe or bronchial spur, compared with histology alone. These results suggest that suprabasal p53 immunostaining is associated with bronchial cancer and might have additive value to predict the biological behavior of pre-neoplastic endobronchial lesions in the population at risk of bronchial cancer.

Widely dispersed p53 mutation in respiratory epithelium. A novel mechanism for field carcinogenesis

Individuals with one aerodigestive tract malignancy have a high incidence of second primary aerodigestive tumors. The mechanism for this field effect has not been determined. We studied an individual with widespread dysplastic changes in the respiratory epithelium but no overt carcinoma. The entire tracheobronchial tree obtained at autopsy was embedded in paraffin, and bronchial epithelial cells were isolated by microdissection. DNA extracted from the microdissected cells was analyzed for point mutations in the p53 tumor suppressor gene. A single, identical point mutation consisting of a G:C to T:A transversion in codon 245 was identified in bronchial epithelium from 7 of 10 sites in both lungs. Epithelium at sites containing the p53 mutation was morphologically abnormal, exhibiting squamous metaplasia and mild to moderate atypia. No invasive tumor was found in the tracheobronchial tree or any other location. Cells from peripheral blood, kidney, liver, and lymph node exhibited no abnormality in the p53 gene. The widespread presence of a single somatic p53 point mutation in the bronchi of a smoker suggests that a single progenitor bronchial epithelial clone may expand to populate broad areas of the bronchial mucosa-a novel mechanism for field carcinogenesis in the respiratory epithelium that may be of importance in assessing individuals for risk of a second primary tumor as well as in devising effective strategies for chemoprevention of lung cancer.