Mutations of the p53 gene in oral squamous‐cell carcinomas from sudanese dippers of nitrosamine‐rich toombak and non‐snuff‐dippers from the Sudan and Scandinavia

Using PCR‐SSCP/DNA sequencing methods, we analyzed 14 oral squamous‐cell carcinomas (OSCCs) and 8 pre‐malignant oral lesions from different Sudanese patients for prevalence of mutations in exons 5 to 9 of the p53 gene in relation to toombak‐dipping status. OSCCs (14 from Sudan, 28 from Scandinavia), and 3 pre‐malignant oral lesions from Sudanese non‐dippers were used as controls. A statistically significant increased incidence in mutations of the p53 gene was found in OSCCs from toombak dippers (93%; 13/14), as compared with those from non‐dippers in Sudan (57%; 8/14) and in Scandinavia (61%; 17/28) respectively. In OSCCs from dippers, mutations were found in exons 5 to 9, while in those from non‐dippers they were found in exons 5, 7, 8, 9, and no mutations were found in exon 8 in any of the OSCCs from Sudan. Certain types of mutations, however, were similar with respect to exposure to toombak. OSCCs from dippers showed 15 transversions, 9 transitions, 3 insertions and one deletion, compared with 7 transversions, 2 transitions and one deletion found in OSCCs from Sudanese non‐dippers, and 9 transversions, 17 transitions and 2 insertions found in those from non‐dippers in Scandinavia. No mutations were found in any of the non‐malignant oral lesions in relation to dipping or non‐dipping status. These findings suggest that (i) the use of toombak plays a significant role in induction of increased p53 gene mutations, (ii) mutations observed were similar to those induced by tobacco‐specific N‐nitrosamines (TSNAs) in experimental animal models and those already reported in toombak dippers, (iii) types of mutations associated with TSNAs were similar in the exposed and the control groups, (iv) a novel mutation in exon 6 was found in the OSCCs from toombak dippers, (v) the p53 exons 5 (codon 130), 6 (codons 190, 216) and 7 (codons 229, 249, 252) mutations are probable hot spots for toombak‐related OSCCs. Further studies are necessary to validate the increased incidence and exon locations of the p53‐gene mutations as a biomarker of malignant transformation in populations in which the oral use of tobacco is habitual. Int. J. Cancer 81:527–534, 1999. © 1999 Wiley‐Liss, Inc.