Previous studies have revealed that patients with oral or esophageal cancer are at higher risk for subsequently developing a second primary malignancy. However, it remains to be determined what association exists between oral cancer and esophageal cancer particularly in Asian countries where squamous cell carcinoma is the predominant type of esophageal cancer. A population-based study was carried out in Taiwan, where the incidence rates of both oral and esophageal squamous cell carcinomas are high, to test the hypothesis that oral cancer or esophageal cancer predisposes an individual to developing the other form of cancer. Our results showed that patients with primary oral cancer (n=45,859) had ten times the risk of second esophageal cancer compared to the general population. Within the same cohort, the reciprocal risk of oral cancer as a second primary in primary esophageal cancer patients (n=16,658) was also increased seven-fold. The bidirectional relationship suggests common risk factors between these two cancers. The present study is not only the first population-based study in Asia to validate the reciprocal relationship between oral and esophageal squamous cell carcinomas, but also will aid in the appropriate selection of high-risk patients for a future follow-up surveillance program.
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