Multiple clonal abnormalities in the bronchial epithelium of patients withlung cancer

Background: Several molecular changes, including loss of heterozygosity (i. e., deletion of one copy of allelic DNA sequences) and alterations in micro satellite DNA, have been detected early in the pathogenesis of lung cancer, even in histologically normal epithelium. In the bronchial epithelium of p atients with lung cancer, we have determined the frequency, size, and patte rns of molecularly abnormal clonal patches. Methods: We studied formalin-fi xed, paraffin-embedded samples from 16 surgically resected lung carcinomas (five squamous cell carcinomas, four small-cell carcinomas, six adenocarcin omas, and one large-cell carcinoma). From each carcinoma, we microdissected foci (each containing about 200 cells) of tumor tissue and equivalent samp les of histologically normal and abnormal epithelium. Furthermore, multiple discontinuous foci of bronchial epithelium were analyzed from methanol-fix ed samples from three additional patients with lung cancer (two with squamo us cell carcinoma and one with adenocarcinoma). We used two-step polymerase chain reaction-based assays involving 12 microsatellite markers at seven c hromosomal regions frequently deleted in lung cancer. Results: Two hundred eighteen foci of nonmalignant bronchial epithelium (195 of histologically n ormal or slightly abnormal epithelium and 23 of dysplastic epithelium) were studied from the 19 surgically resected lobectomy specimens, Thirteen (68% ) of the 19 specimens had at least one focus of bronchial epithelium with m olecular changes. At least one molecular abnormality was detected in 32% of the 195 histologically normal or slightly abnormal foci and in 52% of the 23 dysplastic foci, Extrapolating from our two-dimensional analyses, we est imate that most clonal patches contain approximately 90000 cells. Although, in a given individual, tumors appeared homogeneous with respect to molecul ar changes, the clonally altered patches of mildly abnormal epithelium were heterogeneous, Conclusions: Our findings indicate that multiple small clon al or subclonal patches containing molecular abnormalities are present in n ormal or slightly abnormal bronchial epithelium of patients with lung cance r.