SEQUENTIAL P53 MUTATION ANALYSIS OF PREINVASIVE AND INVASIVE HEAD ANDNECK SQUAMOUS CARCINOMA

Single-stranded conformation polymorphism (SSCP) and direct sequencing were performed on uninvolved mucosa, severe dysplasia and invasive ca rcinoma samples from 20 patients with head and neck squamous carcinoma . Seven (35%) of the non-invasive lesions and 15 (75%) of the invasive carcinomas manifested p53 mutations. Although the majority of mutatio ns were mis-sense, resulting in single amino acid substitution, a sile nt mutation encoding for the same amino acid and 2 non-sense mutations encoding a stop codon were also observed. Mutations in invasive carci noma were mostly in exon 8 and involved codons 296, 288 and 298; non-i nvasive lesions showed more mutations at exons 5 to 7. Five lesions sh owed simultaneous mutations in 2 different exons; in 3 both non-invasi ve and invasive carcinomas showed primary mutation at exons 5 to 7, an d invasive carcinoma showed a secondary mutation at exon 8. Different codon mutations in the same exon between dysplastic and the correspond ing carcinoma samples were found in 2 cases. p53 alterations were not observed in any of the normal mucosa samples. No apparent association between p53 mutations and conventional clinicopathologic parameters, i ncluding DNA content, was found in this cohort. Our study indicates th at (i) p53 alteration is an early event in the genesis of a subset of head and neck squamous carcinomas, (ii) normal mucosa within the resec ted specimens lacked p53 mutation, (iii) sequential mutations of diffe rent exons of the p53 gene suggests accumulation of genetic alteration s during the neoplastic transformation of these lesions and (iv) the d ifference in codon mutation of the same exon between dysplastic and co rresponding carcinoma suggests an independent clonal development. (C) 1995 Wiley-Liss, Inc.