Advances in Brief Use of Allelic Loss to Predict Malignant Risk for Low-grade Oral Epithelial Dysplasia 1 Miriam P. Rosin, Xing Cheng, Catherine Poh, Wan L. Lam, Yongqian Huang, John Lovas, Ken Berean, Joel B. Epstein, Robert Priddy, Nhu D. Le, and Lewei Zhang 2 British Columbia Cancer Agency/Cancer Research Centre, Vancouver, British Columbia, V5Z 4E6 Canada [M. P. R., W. L. L., J. B. E., N. D. L.]; School of Kinesiology, Simon Fraser University, Burnaby, British Columbia, V5A 1S6 Canada [M. P. R., X. C., Y. H.]; Faculty of Dentistry, University of British Columbia, Vancouver, British Columbia, V6T 1Z3 Canada [X. C., C. P., J. B. E., R. P., L. Z.]; Faculty of Dentistry, Dalhousie University, Halifax, Nova Scotia, B3H 3J5 Canada [J. L.]; Vancouver General Hospital, Vancouver, British Columbia, V5Z 1M9 Canada [K. B., J. B. E.]; and School of Dentistry, University of Washington, Seattle, Washington 98195 [J. B. E.] Abstract One of the best approaches to identifying genetic changes critical to oral cancer progression is to compare progressing and nonprogressing oral premalignant lesions. However, such samples are rare, and they require long-term follow-up. The current study used the large archive network and clinical database in British Columbia to study loss of heterozygosity (LOH) in cases of early oral premalignancies, comparing those with a history of progression to carcinoma in situ or invasive cancer and those without a history of progression (referred to as nonprogressing cases). Each of 116 cases was analyzed for LOH at 19 microsatellite loci on seven chromosome arms (3p, 4q, 8p, 9p, 11q, 13q, and 17p). The progressing and nonprogressing cases showed dramat- ically different LOH patterns of multiple allelic losses. An essential step for progression seems to involve LOH at 3p and/or 9p because virtually all progressing cases showed such loss. However, LOH at 3p and/or 9p also occurred in nonprogressing cases. Individuals with LOH at 3p and/or 9p but at no other arms exhibit only a slight increase of 3.8-fold in relative risk for developing cancer. In contrast, individu- als with additional losses (on 4q, 8p, 11q, or 17p), which appeared uncommon in nonprogressing cases, showed 33- fold increases in relative cancer risk. In conclusion, analysis of LOH at 3p and 9p could serve as an initial screening for cancer risk of early premalignancies. Follow-up investiga- tion for additional losses would be essential for predicting cancer progression. Introduction Oral premalignant lesions most often appear clinically as leukoplakia. The criterion for judging the malignant potential of these lesions is based mainly on the presence and degree of dysplasia. Using this criterion, premalignant lesions are classi- fied histologically into stages with increasing risk of developing into invasive SCC, 3 namely: epithelial hyperplasia; mild, mod- erate, and severe dysplasias; and CIS. High-grade preinvasive lesions (severe dysplasia and CIS) are believed to have a high probability of progression into invasive carcinoma and are therefore treated aggressively (1, 2). However, the majority of the low-grade lesions (mild and moderate dysplasia), as well as hyperplasia without dysplasia, do not progress into cancer (1, 3). Because these early lesions constitute the bulk of oral leukopla- kias, and pathohistological stage assignment alone does not predict their malignant potential, a more reliable predictive test needs to be developed. A central dogma of carcinogenesis is that alteration to critical control genes underlies malignant transformation. There- fore, progressing lesions are likely to be genetically different from their morphologically similar nonprogressing counterparts. The identification of such differences would provide genetic markers useful in predicting the behavior of low-grade lesions. As a result, clinicians would be able to identify which patients with low-grade lesions should be managed more aggressively, either by more frequent screening or by early treatment, using traditional approaches such as surgery or newer techniques such as chemopreventive regimes. One of the more sensitive techniques available for studying clonal changes in tumors and premalignant lesions is the use of polymerase chain-based microsatellite analysis for allelic loss. The advantage of the procedure is that it requires only small quantities of DNA yet yields valuable data on the loss of chromosomal regions that contain putative suppressor genes. Hence, we can obtain information on critical genetic events even before the identification of the actual suppressor gene. This approach has been used frequently in head and neck cancers (4 –10). Studies on premalignant lesions have been limited in number and scope due to the difficulty of obtaining suitable specimens for analysis and due to technical problems associated with working with very small lesions and minute amounts of DNA (11–15). However, frequent occurrence of LOH has been demonstrated in oral premalignant lesions, and several regions of loss common to SCCs have been observed in dysplastic Received 8/30/99; revised 10/4/99; accepted 10/7/99. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 1 Supported by a grant from the National Cancer Institute of Canada with funds from the Canadian Cancer Society. 2 To whom requests for reprints should be addressed, at Faculty of Dentistry, University of British Columbia, 2199 Wesbrook Mall, Van- couver, British Columbia, V6T 1Z3 Canada. Phone: (604) 822-6337; Fax: (604) 822-8279; E-mail: lzhang@unixg.ubc.ca. 3 The abbreviations used are: SCC, squamous cell carcinoma; LOH, loss of heterozygosity; CIS, carcinoma in situ. 357 Vol. 6, 357–362, February 2000 Clinical Cancer Research