Yosuke Kishimoto

Mutations associated with carcinomas arising from pleomorphic adenomas of the salivary glands

Pleomorphic adenoma (PA) is the most common benign tumor of salivary glands. Carcinomas in pleomorphic adenomas (CPAs) may arise by malignant transformation of the epithelial components of PAs. Occasionally, transitional zones containing cells with histological features intermediate between those of the benign PA and carcinomatous components of CPA are identified. After careful microdissection of archival microslides, the authors studied 12 cases of CPAs and their attendant adenomatous and transitional areas for mutations in the p53, RB, and K-ras genes, and at chromosomal loci 5q and 9p. The authors failed to find mutations in the K-ras gene or 9p locus. A relatively high rate of mutations (loss of heterozygosity [LOH] and microsatellite alterations) at the p53 gene were detected in CPAs (58%), and at somewhat lower frequencies at the RB gene (33%) and chromosomal location 5q (17%). Mutational frequency in the associated transitional and adenomatous areas were slightly lower than in the corresponding CPAs. No mutations were detected in adenomatous or transitional areas unless they also were present in the corresponding CPAs. Mutations of these three genes were absent in four cases of CPA, and in seven PAs without malignant change. These findings indicate that most CPAs arise from adenomas as the result of mutations in the three genes, especially p53. In addition, other, as yet unidentified genes may also be involved both in the development of PA and in its malignant progression to CPA. Mutational analysis of PAs may provide information of prognostic importance.

K-ras mutations and allelic loss at 5q and 18q in the development of human pancreatic cancers

SummaryConclusionOur findings have implications for early diagnosis and for the identification of patients at increased risk.BackgroundInvasive cancers of the pancreas frequently are preceded by and associated with a spectrum of preneoplastic changes. We investigated the presence of K-ras mutations and allelic loss at 5q and 18q loci in preneoplastic lesions associated with nine cases of invasive pancreatic ductal carcinomas.MethodsWe precisely microdissected 115 foci of normal, preinvasive, and invasive foci from paraffinembedded sections.Results1.K-ras mutations occur early in the pathogenesis of pancreatic adenocarcinoma. Mutations were identified in multiple preneoplastic foci associated with all six cases in whichras mutations were present in the corresponding invasive cancers, including nearly all foci of mucous cell and atypical hyperplasia, in some cases of papillary hyperplasia (40%), and in one example of morphologically normal epithelium.2.Ras mutations in preneoplastic foci are widespread, occur distant from the invasive tumor, and may present multiple mutations. Two, and in one case three, different types of K-ras mutations were found in separate preneoplastic foci from three individual cases.3.Evidence for a “second hit” in theras gene (i.e., loss of wild-type allele or amplification of the mutant allele) was present in some tumors and may be associated with the invasive process.4.In contrast toras mutations, limited data suggest that loss of heterozygosity (LOH) at 5q and 18q are relatively late events.

DNA analysis at p53 locus in carcinomas arising from pleomorphic adenomas of salivary glands: Comparison of molecular study and p53 immunostaining

Where and how frequently p53 abnormalities are involved in the development of pleomorphic adenoma (PA) and its malignant progression to carcinoma was investigated. The presence of p53 gene abnormalities was analyzed in eight patients with carcinoma in pleomorphic adenoma (CPA) by polymerase chain reaction (PCR)‐based assays and immunohistochemistry. Normal salivary gland tissue, adenomatous, transitional and carcinomatous areas were microdissected from archival microslides and analyzed for allelic deletions of the p53 gene using two microsatellite markers at the p53 locus; dinucleotide (CA)n repeat and pentanucleotide (AAAAT)n repeat. Loss of heterozygosity (LOH) of the p53 gene was detected in 5796 of adenomas, 86% of transitional lesions and 86% of carcinomas. In contrast, overexpression of p53 oncoprotein was noted immunohistochemically in 13% of adenomas, 50% of transitional areas and 75% of carcinomas. All of the tumors with immunoreactivity for p53 oncoprotein demonstrated LOH. Moreover, when LOH was present in adenomatous or transitional areas, the identical LOH was always detected in the corresponding carcinomatous areas in the same CPA tumors. These findings indicate that p53 gene mutation is an early event and occurs frequently at an early stage of precancerous lesions and may be responsible for most cases of malignant transformation of PA.

Frequent loss of the short arm of chromosome 9 in resected non-small-cell lung cancers from Japanese patients and its association with squamous cell carcinoma

We analyzed 87 Japanese non-small-cell lung carcinomas (NSCLC), including 30 squamous cell, 51 adenocarcinomas and 6 large-cell carcinomas for loss of heterozygosity (LOH) on the short arm of chromosome 9, and we correlated our findings with clinicopathological features. We used four polymorphic microsatellite markers on 9p (interferon A gene, D9S171, D9S126, and D9S169), which flank the critical region (9p21-22) involved in lung cancer. We observed alterations of DNA sequences at 9p in NSCLC (27 of 82 informative cases or 33%). Concordance among the four markers was high (87%), indicating that the deletions often were relatively large. The 27 genetic alterations observed on 9p include 26 examples of LOH, 1 homozygous deletion, and 1 case with LOH and evidence of microsatellite alteration characterized by shift in band mobility. We noted a high frequency of LOH at 9p especially in, squamous cell carcinoma (17 of 29 informative cases or 59%) and in poorly differentiated NSCLC (12 of 23 informative cases or 52%). There was no correlation between LOH at 9p and the other clinical parameters, including survival, gender, tumor size and the presence of regional or distant metastases. In contrast to other reports we found only rare instances of homozygous deletions (1%) and microsatellite alteration showed as a mobility shift (1%). Our findings demonstrate that LOH at the short arm of chromosome 9 is correlated with squamous cell and poorly differentiated carcinomas in Japanese patients with NSCLC.

Molecular genetic changes in the pathogenesis of lung cancer

Human lung cancer is a complex genetic disease resulting from a series of inherited and somatically occurring defects in a number of critical genes. These genetic events, produced in part by carcinogen exposure, include chromosomal deletion, rearrangement, and mutation, and lead to inactivation or activation of certain target genes. Recent data showed these genes to include both recessive oncogenes such as the retinoblastoma gene and dominantly acting oncogenes such as the myc and ras family members.