Patients with primary head and neck malignancies have a 3–7% yearly incidence of second primary cancers. It is thought that these second primary cancers arise independently following exposure to a common carcinogen by a process that has been called field cancerization. Since mutations in the p53 tumor suppressor gene represent a genetic alteration occurring during the evolution of premalignant lesions to malignancies of the upper aerodigestive tract, we analyzed mutations in the p53 gene of patients with cancer of the head and neck who developed second primary tumors of the upper aerodigestive tract epithelium to test the field cancerization hypothesis.
DNA was extracted from primary head and neck cancers and second primary cancers of 31 patients. DNA from exons 5–8 of the p53 gene was analyzed by the single strand conformation polymorphism technique to identify the locations of the mutations in different regions of the gene. DNA from 6 patients was also sequenced by the chain termination method to confirm the presence of mutations and determine the base substitutions. Twenty-one of the 31 patients had 1 or more p53 mutations. In all 21 cases the genetic lesions were discordant such that the presence or location of the mutations in the initial primary cancer differed from those of the second and third primary cancers. In each of the five patients with mutations in both primary tumors, the mutations occurred in different regions of the p53 gene. Of the other 16 patients, 8 had a p53 mutation in the first primary but not the subsequent primary cancer and the other 8 had no mutation in the initial primary but did have a mutation in subsequent primary cancers. Sequencing confirmed the single strand conformation polymorphism analysis and showed that 73% of the mutations were transitions.
The discordant p53 mutations in second primary cancers arising in patients with primary epithelial cancer of the upper aerodigestive tracts suggest that these cancers arise as independent events. These observations provide the first demonstration of a molecular basis for field cancerization effects in cancers of the upper aerodigestive tract.
This study was partially supported by grants from the National Cancer Institute and NIH (RO1 CA45187) (J. A. R.), by National Institute of Cancer Training Grant CA09611 (J. A. R.); by gifts to the Division of Surgery from Tenneco and Exxon for the Core Lab Facility; by M. D. Anderson Cancer Center Support Grant NCI CA16672, and by grants from the Rippel Foundation and the Mathers Foundation.