TP53 abnormalities are frequent and early events in the sequential pathogenesis of gallbladder carcinoma.

BACKGROUND: Gallbladder carcinoma (GBC) is a frequent neoplasm in Hispanic and native American populations. GBC is preceded by gallstones, chronic cholecystitis and dysplastic changes of the gallbladder epithelium. The knowledge of the molecular events involved in its pathogenesis is scarce. AIMS: We investigated the role of TP53 inactivation in the sequential pathogenesis of GBC. METHODS: Invasive tumor-, dysplastic- and histologically normal GB epithelial-cells were obtained from archival formalin-fixed tissues from GBC and GB from gallstone patients without GBC. Normal GB epithelia from 5 non-gallstone specimens were also studied. DNA extracted was examined for loss of heterozygosity (LOH) using 2 microsatellite markers and for TP53 mutations at exons 5 to 8. RESULTS: GBCs demonstrated a high frequency of LOH (81%) and mutation (67%), and both abnormalities indicating gene inactivation were detected in 52%. Similar frequency of TP53 abnormalities and gene inactivation (38%) were detected in their accompanying normal and dysplastic epithelia. Noteworthy, one third of normal and dysplastic epithelia obtained from GBs of gallstone patients without GBC demonstrated either TP53 allele loss or mutation, but gene inactivation was less frequent (11%). Most mutations affected exons 5 and 7, and they were more frequently missense point mutations. The same TP53 mutation was detected in only a subset (27%) of comparisons between non-malignant epithelia adjacent to GBCs, indicating that TP53 mutation occurs independently at several epithelial foci. CONCLUSIONS: These findings indicate that TP53 abnormalities are early and frequent events in the pathogenesis of GBC, starting from chronic cholecystitis.

Distinct K-ras mutation pattern characterizes signet ring cell colorectal carcinoma.

PURPOSE: Signet ring cell colorectal carcinoma (SRCCC) represents a unique, infrequent, and highly malignant variant of colorectal cancer. To understand the pathogenesis of SRCCC, we investigated its molecular abnormalities and compared them with those of the usual type of colorectal adenocarcinoma. EXPERIMENTAL DESIGN: Microdissected archival paraffin-embedded tissue from 16 SRCCCs and 27 non-SRCCCs was used to determine the frequency and pattern of mutation at codons 12, 13, and 61 of K-ras. A subset of tumors was examined for TP53 mutations at exons 5-8 and allele loss and genetic instability using seven microsatellite and two mononucleotide markers. RESULTS: Comparable data on TP53 mutation, allele loss, and microsatellite instability were found between SRCCC and non-SRCCC. However, SRCCCs demonstrated a distinct pattern of K-ras mutation with a significantly lower frequency of mutations at codons 12 and 13 (13% versus 48%, P = 0.02) as compared with the non-SRCCCs. Four cases (25%) of SRCCC demonstrated the same A:T transversion at the third base position of K-ras codon 61 (CAA to CAT; Gln to His). No such point mutation was detected in non-SRCCCs or in the 30 gastric and 4 urinary bladder signet ring cell carcinomas examined. CONCLUSIONS: Our findings suggest that a distinct pattern of K-ras mutation is present in SRCCC, including a specific codon 61 mutation that has rarely been reported in human neoplasms.

Characteristic genetic alterations in lung cancer.

Our understanding of the molecular pathology of lung cancer is advancing rapidly with several specific genes and chromosomal regions being identified. Lung cancer appears to require many mutations in both dominant and recessive oncogenes before they become invasive. Several genetic and epigenetic changes are common to all lung cancer histologic types, while others appear to be tumor-type specific. The identification of those specific genes undergoing such mutations and the sequence of cumulative changes that lead the neoplastic changes for each lung tumor histologic type remain to be fully elucidated. Recent findings in normal and preneoplastic bronchial epithelium from lung cancer patients and smoker subjects suggest that genetic changes may provide in this neoplasm new methods for early diagnosis, risk assessment, and for monitoring response to chemoprevention.

Smoking molecular damage in bronchial epithelium.

Our understanding of the molecular pathology of lung cancer is advancing rapidly with several specific genes and chromosomal regions being identified. Lung cancer appears to require many mutations in both dominant and recessive oncogenes to possess malignant phenotypes. Several genetic and epigenetic changes are common to all lung cancer histologic types, while others appear to be cell type specific. However, specific roles of the genes undergoing mutations and the order of cumulative molecular changes that lead to the development of each lung tumor histologic type remain to be fully elucidated. Recent findings of molecular abnormalities in normal appearing and preneoplastic bronchial epithelium from patients with lung cancer and chronic smokers suggest that genetic changes may serve as biomarkers for early diagnosis, risk assessment and monitoring response to chemoprevention.

Fragile histidine triad gene abnormalities in the pathogenesis of gallbladder carcinoma.

There is limited information about the molecular changes involved in the pathogenesis of gallbladder carcinoma (GBC). Our recent allelotyping analyses have indicated that chromosome 3p loss of heterozygosity (LOH), including the fragile histidine triad (FHIT) candidate tumor-suppressor gene locus at 3p14.2, is frequently detected in this neoplasm. To investigate the role of the FHIT abnormalities in the multistage sequential development of GBC, 33 formalin-fixed paraffin-embedded invasive GBC specimens and 76 accompanying histologically normal (n = 43) and dysplastic (n = 33) epithelia were examined by immunostaining for expression of Fhit protein. Allele loss at the FHIT gene locus (3p14.2) was studied in all GBCs and in a subset of accompanying gallbladder epithelia by polymerase chain reaction-based LOH analysis, using three 3p14.2 microsatellite markers. In addition, histologically normal epithelium from chronic cholecystitis (n = 19) and dysplasia (n = 13) from gallbladder specimens without cancer were examined for immunostaining and LOH. There was a progressive increase in both the frequency of loss of Fhit expression and LOH at FHIT with increasing severity of histopathological changes. FHIT abnormalities were occasionally demonstrated in histologically normal gallbladder epithelium. Dysplastic foci demonstrated frequent reduction or absence of Fhit immunostaining (38 to 55%) and FHIT allelic loss (33 to 46%). In invasive tumors, these abnormalities were even higher, with 79% reduction or absence of Fhit immunostaining and 76% FHIT allele loss. A high correlation (70%) was observed between Fhit immunostaining abnormalities and allele loss in GBC specimens (P < 0.05). Although a high frequency of FHIT locus breakpoints were detected in both invasive and dysplastic gallbladder specimens, no intronic homozygous deletions on FHIT were detected in GBCs. FHIT gene abnormalities are nearly universal in GBC and these changes are detected early in the sequential development of this neoplasm. Our findings indicate that the FHIT gene is one of the chromosome 3p putative tumor suppressor genes involved in the pathogenesis of this highly malignant neoplasm.