The epidemiology of oral premalignant lesions, oral cancer and second primary cancers

Oral carcinogenesis is a complex pathway that involves various factors such as tobacco, alcohol, nutrition and genetic components. It is of importance to study oral premalignant lesions and second primary oral cancers in addition to oral cancer in order to understand the full spectrum of oral carcinogenesis. A case-control study was conducted in Kerala, India to examine potential risk and protective factors for oral premalignant lesions, including oral leukoplakia (n = 927), oral submucous fibrosis (n = 170), erythroplakia (n = 100), multiple premalignant lesions (n = 108) and controls (n = 47,773). Data from a hospital-based case-control study was analyzed to evaluate marijuana smoking, passive smoking, mutagen sensitivity and oral cancer risk including 93 oral cancer cases and 176 controls at the Memorial Sloan-Kettering Cancer Center (MSKCC). The Surveillance, Epidemiology and End Results (SEER) data from 1973 to 1998 was used to estimate standardized incidence ratios for second primary cancers following first primary oral cancer, to assess the effect of radiotherapy on the risk of second primary cancers and to examine survival patterns of second primary oral cancer. Tobacco chewing was found to be a major risk factor for oral premalignant lesions. Tobacco smoking and alcohol drinking elevated the risk of several oral premalignant lesions. Higher body mass index and socioeconomic status were associated with a decreased risk of several oral premalignant lesions. Marijuana smoking and passive smoking were not strongly associated with oral cancer, but our sample size may have limited power to detect moderate associations. An excess of second primary cancers following first primary oral cancers was observed. Radiation therapy was identified as a risk factor for second primary cancers that follow an oral cancer. Second primary oral cancer cases had lower survival rates than did first primary oral cancer cases. Our results on the risk and protective factors for oral premalignant lesions, oral cancer and second primary cancers may contribute to the understanding of the natural history and etiology of the diseases. Such an understanding is critical in setting up preventive strategies to reduce the incidence of oral cancer and second cancers, to slow down the progression of cancer and to improve survival of the disease.