In Gujarat, India, 6718 industrial workers, over 35 years of age, with oral leukoplakia (confirmed clinically and microscopically), were studied. After 2 years, 4762 (71%) of the individuals were re-examined. The buccal mucosa was the most common site of occurrence; 98.3% of these individuals had oral habits, with smoking alone or smoking in combination with "pan" or "supari" chewing accounting for 74.9% of the habit forms. Six individuals (0.13%) with oral leukoplakia developed oral carcinomas within 2 years. This incidence of malignant transformation was equivalent to 63/100,000 per year, which far exceeds that of new oral cancers expected even in high-risk populations. While 57.3% the leukoplakic lesions remained unchanged during a 2-year interval, 31.6% disappeared and 11% had an altered appearance. This study confirmed the precancerous nature of oral leukoplakia.

In Gujarat, India, 57,518 industrial workers over 35 years old were examined for oral lesions. At a two-year interval, 43,654 workers were re-examined. Biopsies were taken from 13,223 lesions. In the initial examination, 29 oral cancers were diagnosed, representing a prevalence rate of 50/100,000. After two years, 22 new oral cancers were diagnosed, representing an incidence rate of 25/100,000 per year. Over 90% were squamous carcinomas, with the majority of lesions occurring in the oropharynx and tongue. All patients who developed squamous carcinomas had tobacco habits, while 85% of the entire study population had oral habits in some form. Their most common habits were smoking tobacco alone or in combination with chewing "pan"/"supari." Of the carcinomas that developed during a two-year interval, 62% appeared in previously normal appearing mucosa. Leukoplakia was the only oral lesion that proved to be precancerous, with a transformation rate of 0.13% in a two-year interval.

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