Etiology of Oral Cancer

Etiology of Oral Cancer Elsy-Britt Schildt, M.D., Department of Oncology, University Hospital, S-901 85 Umeå, Sweden. Oral cancer is a disease with increasing incidence in most West European countries. In Sweden in 1995, intraoral cancer accounted for 1.4% and 0.8% of malignant tumours among men and women respectively. The disease has a bad prognosis and approximately half of the patients will die of their disease. The aim of this investigation was to focus on the relationship between oral cancer and a suite of potential risk factors. The prime focus was to investigate the risk of snuff use but smoking to­ bacco, alcohol consumption, infections, dental factors, dental X-ray, iron deficiency, occupations and occupational exposures were also studied using the case-control design. The study was con­ ducted in Northern Sweden and encompassed 410 cases and as many controls. Furthermore, two molecular epidemiological studies were done regarding the relationship between exposure factors and certain biological parameters of tumours. The use of oral snuff is an increasingly common habit in Sweden. Contrary to previous American studies of cancer risk from oral snuff use, this study showed no elevated risk for oral cancer. Smoking was an important risk factor for oral cancer, but this was restricted to current smokers. Alcohol consumption showed a clear dose-response relationship to oral cancer, and the combina­ tion with smoking increased the risk further. Moreover, the case-control study strongly indicated recurrent HSV-1 infections as an independent causative factor in oral cancer, particularly when the infection was on the lip. Dental factors like different kinds of fillings, fixed prosthesis or removable dentures were not associated with in­ creased risks, nor were dental X-rays. Pulp industry workers and wood or wood product workers were found to have increased risk for oral cancer. Smoking and alcohol in addition increased the risk. Exposure to phenoxyacetic acids indicated an increased risk. Oral infections, and HSV-1 infections in particular, were associated with an increased risk for oral cancer in patients with p53 positive tumours as demonstrated by immunohistochemistry (IHC). However, this relation was not found in patients with p53 mutated tumours confirmed by PCR techniques. This suggests that HSV-1 infection, directly or indirectly, can inactivate p53 function by binding of wild type protein. No association between smoking and p53 positive tu­ mours was found. A new non-random deletion in exon 8 in oral squamous cell carcinoma was found. The cause and clinical significance of this new 14 base pair deletion is unknown. Eighty percent of the patients with the deletion were women. No correlation was found for the deletion group with the known risk factors for oral cancer such as smoking.