Path. Res. Pract. 189,1169-1180 (1993) Ultrastructural Variations and Assessment of Malignant Transformation Risk in Oral Leukoplakia Introduction S. Kannan, P. Balaram, M. Radhakrishna Pillai, G. Jagadeesh Chandran and M. Krishnan Nair Regional Cancer Centre, Thiruvananthapuram, India C.C. Kartha Sree Chitra Thirunal Institute for Medical Sciences and Technology, Thiruvananthapuram, India J. Augustine Department of Pathology, Medical College, Thiruvananthapuram, India L. Sudha and M. K. Mangalam Dental College, Thiruvananthapuram, India SUMMARY Oral cancer is the most common malignancy in India, having a well defined precancerous state, leukoplakia. Various follow-up studies have shown that only 4 to 18% of oral leukoplakia lesions subsequently progress into invasive malignancy over a period of time. This study evaluates the potential of electron microscopy in the early detection of malignant changes in leukoplakia. The study revealed that of the 25 leukoplakia lesions examined, 7 showed changes akin to malignancy. Predominant ultrastructural alterations observed were reduplication and discontinuity of the basal lamina, basal cells with pleomorphic and bizarre nuclei containing perichromatin and interchromatin granules, prominent intercellular spaces and poorly formed desmosomes. Since none of these changes were evident under light microscopy the study demonstrates the value of electron microscopy in evaluating oral carcinogenesis. A long term follow-up of such patients is needed to understand the prognostic implications of these ultrastructural variation and how they can be used as a base line for better light microscopic evaluation. Oral cancer regrettably still has a high mortality rate. 4% in females are due to oral cancer10. Of particular concern to us is the fact that Thiruvananthapuram District in South India has one of the highest incidence rates of oral cancer in the world making this a key problem for health professionals 16 . Almost half the patients who have oral cancer die of the disease. It is also the most common neoplasm in India, with almost 30% of all cancers being in the oro-pharyngeal region and at least 56,000 new cases occurring each year10. Furthermore almost 7% of all cancer deaths in males and © 1993 by Gustav Fischer Verlag, Stuttgart The major reason for this high mortality rate of oral cancer is late diagnosis with lesions that are large, deeply invasive and often metastatic to regional lymph nodes 24 • In 0344-0338/93/0189-1169$3.50/0