Second Base Of Codon Research Articles

TGIF1 is a Potential Candidate Gene for High Myopia in Ethnic Kashmiri Population

Purpose: High myopia is a complex disorder that imposes serious consequences on ocular health. Linkage analysis has identified several genetic loci with a series of potential candidate genes that reveal an ambiguous pattern of association with high myopia due to population heterogeneity. We have accordingly chosen to examine the prospect of association of one such gene [transforming growth β-induced factor 1 (TGIF1)] in population that is purely ethnic (Kashmiri) and represents a homogeneous cohort from Northern India.Methods: Cases with high myopia with a spherical equivalent of ≥−6 diopters (D) and emmetropic controls with spherical equivalent within ±0.5 D in one or both eyes represented by a sample size of 212 ethnic Kashmiri subjects and 239 matched controls. Genomic DNA was genotyped for sequence variations in TGIF1 gene and allele frequencies tested for Hardy–Weinberg disequilibrium. Potential association was evaluated using χ2 or Fisher’s exact test.Results: Two previously reported missense variations C > T, rs4468717 (first base of codon 143) changing proline to serine and rs2229333 (second base of codon 143) changing proline to leucine were identified in exon 10 of TGIF1. Both variations exhibited possibly significant (p < 0.05) association with the disease phenotype. Since the variant allele frequency of both the single-nucleotide polymorphisms in cases is higher than controls with odds ratio greater than 1.Therefore, variant allele of both the single-nucleotide polymorphisms represents the possible risk factor for myopia in the Kashmiri population. In silico predictions show that substitutions are likely to have an impact on the structure and functional properties of the protein, making it imperative to understand their functional consequences in relation to high myopia.Conclusions: TGIF1 is a relevant candidate gene with potential to contribute in the genesis of high myopia.

A novel p16INK4A mutation associated with esophageal squamous cell carcinoma in a high risk population

This study describes identification of p16INK4A sequence variants and their potential association with esophageal squamous cell carcinoma (ESCC) in a high risk population from Kashmir, India. We report a novel 7 base pair exon 2 deletion in 22 out of 106 (~20%) surgically resected tumor samples. The deletion beginning at the second base of codon 103, results in a frame shift causing premature termination of the protein at codon 142, with structural and functional consequences predicted by insilico analysis. The described mutation is a previously unreported variant of p16INK4A, perhaps representing a founder mutation unique to the population.

Rapid Screening Assay for KRAS Mutations by the Modified Smart Amplification Process

Previously, the smart amplification process version 2 (SMAP-2) was developed to detect mutations from tissue and in crude cell lysates and has been used for rapid diagnosis of specific somatic mutations with single-nucleotide precision. The purpose of this study was to develop a rapid and practical method to detect cancer and metastasis in specimens using the SMAP-2 assay. We developed modified SMAP-2 assays that enabled detection of any change in a single codon using a single assay. Rapid SMAP-2 screening assays are suitable for routine clinical identification of critical amino acid substitutions such as codon 12 mutations in KRAS. Primers bracketing the first two nucleotides of KRAS codon 12 were designed so that all possible alleles would be amplified by the SMAP-2 assay. In combination with the peptide nucleic acid (PNA) with exact homology to the wild-type allele, our assay amplified all mutant alleles except for the wild-type sequence. With this new assay design (termed PNA-clamp SMAP-2), we could detect KRAS mutations within 60 minutes, including sample preparation. We compared results from PNA-clamp SMAP-2 assay, polymerase chain reaction-restriction fragment length polymorphism, and direct sequencing of clinical samples from pancreatic cancer patients and demonstrated perfect concordance. The PNA-clamp SMAP-2 method is a rapid, simple, and highly sensitive detection assay for cancer mutations.

Novel mutation in the ligand-binding domain of the androgen receptor gene (1790p) associated with complete androgen insensitivity syndrome

Mutations in the X-linked androgen receptor (AR) gene cause androgen insensitivity syndrome (AIS), resulting in an impaired embryonic sex differentiation in 46,XY genetic men. Complete androgen insensitivity (CAIS) produces a female external phenotype, whereas cases with partial androgen insensitivity (PAIS) have various ambiguities of the genitalia. Mild androgen insensitivity (MAIS) is characterized by undermasculinization and gynecomastia. Here we describe a 2-month-old 46,XY female patient, with all of the characteristics of CAIS. Defects in testosterone (T) and dihydrotestosterone (DHT) synthesis were excluded. Sequencing of the AR gene showed the presence in exon 6 of a T to C transition in the second base of codon 790, nucleotide position 2369, causing a novel missense Leu790Pro mutation in the ligand-binding domain of the AR protein. The identification of a novel AR mutation in a girl with CAIS provides significant information due to the importance of missense mutations in the ligand-binding domain of the AR, which are able to induce functional abnormalities in the androgen binding capability, stabilization of active conformation, or interaction with coactivators.

Two novel mutations 685del 1 and D129G in the low-density lipoprotein receptor gene in a compound heterozygote Chinese family with familial hypercholesterolemia

DNA sequencing analysis was used to scan the genes in a Chinese family with clinically diagnosed autosomal genetic hypercholesterolemia. Two mutations were identified in exon 4 of the low-density lipoprotein receptor gene, which is the possible molecular mechanism of etiology of the family. The proband's extremely high level of serum cholesterol and the related manifestations suggested that he was a familial hypercholesterolemia homozygote and that his parents were in a relatively milder condition. DNA sequencing revealed that the proband had an abnormal pattern of exon 4 of the low-density lipoprotein receptor gene due to a heterozygosity (A/G) at nucleotide 386 and a heterozygous single-base deletion (A) at 685. Nucleotide 386 is the second base of codon 129, and A→G mutation (D129G) changed this codon from Asp GAC to Gly GGC. The single-base deletion of A at 685 (685del 1) is a frameshift mutation. It changes the phase of triplets, so that all codons are misread after this site of mutation; consequently, the protein expressed by the gene must be abnormal in structure and function. DNA analysis of the other family members showed that the 2 mutations should be respectively located in different alleles of the proband. Both of the 2 mutations have not been reported previously.

Establishment and characterization of a tumorigenic cell line from areca quid and tobacco smoke-associated buccal carcinoma

A cell line, TW2.6, has been established from the surgically resected specimen of an untreated primary squamous cell carcinoma of the buccal mucosa from a 48-year-old man who was an areca quid chewer and tobacco smoker. TW2.6 cells exhibited morphological features of keratinocytes and replicated rapidly in culture with a doubling time of 24h. The karyotype showed human chromosomes with high hyperdiploidy and complex rearrangements. Western blotting showed pronounced expression of p53 and moderate expression of p21(CIP1). The baseline expressions of p27(KIP1) and p16(INK4a) were barely detectable. Low levels of Bax and Fas were found in TW2.6 cells but Bcl-2 expression was more readily observed. Mutational analysis of p53 gene revealed an A-->G transition at the second base of codon 220, resulting in amino acid substitution from tyrosine to cysteine in the protein. Functional analysis showed that TW2.6 was unable to activate the p53-specific PUMA promoter. Lipofectamine 2000 and calcium phosphate precipitation technique offer good transfection efficiencies for TW2.6 cells and may be used in future transfection experiments. A xenograft-SCID mouse tumor model was established for TW2.6. Histological examination demonstrated that the engrafted tumors maintained the morphological features of a squamous cell carcinoma. It is thought that the establishment of tumorigenic TW2.6 cell line provides a valuable model for AQ and tobacco smoke-associated buccal carcinoma.

Translesion Synthesis Past Tamoxifen-Derived DNA Adducts by Human DNA Polymerases η and κ

The long-term treatment of tamoxifen (TAM), widely used for adjuvant chemotherapy and chemoprevention for breast cancer, increases a risk of developing endometrial cancer. A high frequency of K-ras mutations has been observed in the endometrium of women treated with TAM. Human DNA polymerase (pol) eta and pol kappa are highly expressed in the reproductive organs and are associated with translesion synthesis past bulky DNA adducts. To explore the miscoding properties of alpha-(N2-deoxyguanosinyl)tamoxifen (dG-N2-TAM), a major TAM-DNA adduct, site-specifically modified oligodeoxynucleotides containing a single diastereoisomer of trans or cis forms of dG-N2-TAM were prepared by phosphoramidite chemical procedure and used as templates. The primer extension reaction catalyzed by pol kappa deltaC, a truncated form of pol kappa, extended more efficiently past the adduct than that of pol eta by incorporating dCMP, a correct base, opposite the adduct. With pol eta, all diastereoisomers of dG-N2-TAM promoted small amounts of direct incorporation of dAMP and deletions. With pol kappa deltaC, dG-N2-TAM promoted small amounts of dTMP and/or dAMP incorporations and deletions. The miscoding properties varied depending on the diastereoisomer of dG-N2-TAM adducts and the DNA pol used. Steady-state kinetic studies were also performed using either the nonspecific sequence or the K-ras gene sequence containing a single dG-N2-TAM at the second base of codon 12. With pol eta, the bypass frequency past the dA x dG-N2-TAM pair positioned in the K-ras sequence was only 2.3 times lower than that for the dC x dG-N2-TAM pair, indicating that dG-N2-TAM in the K-ras sequence has higher miscoding potential than that in the nonspecific sequence. However, with pol kappa deltaC, the bypass frequency past the dC x dG-N2-TAM pair was higher than that of the dT x dG-N2-TAM pair in both sequences. The properties of pol eta and pol kappa are consistent with the mutagenic events attributed to TAM-DNA adducts.

The N131S Mutation in the von Hippel-Lindau Gene in a Japanese Family with Pheochromocytoma and Hemangioblastomas

von Hippel-Lindau (VHL) disease (VHLD) is a hereditary autosomal dominant syndrome that causes various benign and malignant tumors. VHLD is caused by mutations in the VHL tumor suppressor gene. Here, we report a mutation in the VHL gene in a Japanese family with VHLD type 2A, characterized by pheochromocytoma (PHE), and hemangioblastomas (HAB) in both the retina and thoracic spinal cord but without renal cell carcinoma (RCC). We identified a heterozygous A to G point mutation at the second base of codon 131 of the VHL protein (pVHL). This mutation was predicted to convert codon 131 from asparagine to serine (N131S). Although most mutations in VHLD type 2A have been detected in the alpha domain of pVHL, the present mutated amino acid was located at the region encoding the beta domain of pVHL. Previous patients with the N131K or N131T mutation in pVHL developed VHLD type 2B with RCC or VHLD type 1 without PHE, respectively. We also identified somatic loss of heterozygosity (LOH) at chromosome 3p25-26 in the adrenal tumor of the patient. The results of our study suggest that not only the location of mutation but also the altered amino acid may be critical for determining the clinical phenotype of VHLD. LOH was associated with the development of PHE in a patient with the N131S mutation in pVHL.

Renal apolipoprotein A-I amyloidosis associated with a novel mutant Leu64Pro

Apolipoprotein A-I amyloidosis (Apo A-I) is an inherited systemic disease that results from the pathologic deposition in tissues throughout the body of fibrils composed of Apo A-I-related molecules. This disorder has been linked to mutations occurring within the coding region of the Apo A-I gene and, to date, 11 such substitutions have been documented. In 4 of these cases, the kidney was the target organ of the disease process. The authors report their studies on a patient with renal amyloidosis and a heretofore undescribed alteration in the amyloidogenic precursor protein. Analyses of genomic DNA evidenced a transition in the second base of codon 64 (T-->C) in one Apo A-I allele that resulted in the replacement of leucine by proline at position 64 (Leu64Pro). Additionally, fibrils extracted from the kidney and characterized chemically were found to be composed almost exclusively of an approximately 96-residue N-terminal Apo A-I fragment that contained the Leu64Pro substitution. These studies have provided further evidence for Apo A-I amyloidogenicity and the propensity of certain mutants to deposit in renal parenchyma.

Detection of K-ras gene mutation in fecal samples from elderly large intestinal cancer patients and its diagnostic significance

To study the diagnostic significance of K-ras gene mutations in fecal samples from elderly patients with large intestinal cancer. DNA was extracted in the fecal and tissue samples from 23 large intestinal cancer patients, 20 colonic adenomatoid polypus patients and 20 healthy subjects. The K-ras gene mutations at the first and second bases of codon 12 were detected by the allele specific mismatch method. The K-ras gene mutation was 56.52%(13/23) in the large intestinal cancer patients, which was notably higher than that in the normal subjects whose K-ras gene mutation was 5%(1/20) (chi (2)=12.93, P<0.001). There was no significant difference in comparison with that of colonic adenomatoid polypus patients whose K-ras gene mutation was 30%(6/12) (chi (2)=3.05, P>0.05). The K-ras gene mutation at the second base of codon 12 was 92.13%(12/13) in the large intestinal cancer patients. There was no significant difference between the detection rate of K-ras gene mutation in the fecal and tissue samples (chi (2)=9.35, P<0.01). Our results indicate that detection of the K-ras gene mutations in fecal samples provides a non-invasive diagnostic method for the elderly large intestinal cancer patients. Its significance in the early diagnosis of large intestinal cancer awaits further studies.

Genetics of familial amyloidotic polyneuropathy in a Hong Kong Chinese kindred.

Familial amyloidotic polyneuropathy type 1 (FAP1, MIM176300) is an autosomal dominant disease caused by mutations in the transthyretin (TTR) gene. An extended Chinese kindred of FAP1 was first reported in Hong Kong in 1989, three of the four histologically proven subjects have deceased. TTR gene mutations were not studied then. A DNA-based diagnosis was performed on FAP1 by restriction analysis and direct DNA sequencing was carried out on a symptomatic member of this family who had undergone a liver transplantation. It showed a substitution of thymine by cytosine in the second base of codon 30 in exon 2 of the TTR gene, with the creation of a novel HhaI restriction endonuclease site. Valine is substituted by alanine (V30A) in the mutant TTR. Both restriction analysis and direct sequencing revealed the same mutation in one of the two asymptomatic siblings. This mutation was first reported in a FAP1 family of German descent.

Novel mutations of neurofibromatosis type 1 gene in small cell lung cancers.

Mutations in the GTPase-activating protein-related domain (GRD) of the von Recklinghausen neurofibromatosis type 1 (NF1) gene have been reported in several tumors that were not previously associated with NF1. We analyzed 37 cases of lung cancer, including 9 cases of small cell carcinoma, to detect mutations in this domain. DNA was extracted from the tumors, and single-strand conformation polymorphism and direct sequencing were used to detect mutations. Three cases of small cell carcinoma had mutations in NF1-GRD. There were two incidences of an A --> G transition at the second base of codon 1415 resulting in Glu --> Gly substitution, and one incidence of an A --> G transition at the third base of codon 1411 (Pro) without amino acid substitution. All three patients had both hilar and mediastinal lymphatic metastasis. A mutation in this region could imply a poor prognosis.

Transitions and Transversions in Ki-Ras Gene in Colorectal Cancers in Mexican Patients

An important increase in the incidence of colorectal cancers has been detected in the last 15 years in Mexico. This fact has been attributed to several causes, including the change in diet acquired from industrialized countries. Various groups have studied the mutational pattern of oncogenes, including Ki-ras gene, in colorectal cancers from different human populations. The aim of this work was to study the prevalence of mutations at codons 12, 13 and 61 of the Ki-ras gene in 37 colorectal tumors from Mexican patients and to correlate them with clinical data. Point mutations were studied in 37 colorectal cancers at codons 12 and 13 of the Ki-ras gene, using PCR followed by RFLP. We also performed PCR-SSCP to identify mutations at codon 61. We confirmed mutations by sequence analysis in all the altered codons. Our results indicated that 24.3% of the tumors presented mutations at codon 12, 5.4% at codon 13, and 2.7% at codon 61 of the Ki-ras gene. We found that 75% of these mutations were transitions and 25% transversions. The overall results indicated that the frequency of Ki-ras mutations in colorectal cancers in a sample of a Mexican population (Mexico City) was 32.4%, which is similar to that reported in other populations. We did not find a correlation between the Ki-ras mutations and gender, location of the tumor, or Dukes' stage, but survival of the patient without recurrence was statistically significant. The study of colorectal cancer indicated that in a Mexican population Ki-ras mutations were present in tumors of patients who survived without tumor recurrence. Most of them were transitions in the first and second base of codon 12.

Associations between family history of colorectal cancer and genetic alterations in tumors.

A family history of colorectal cancer has been consistently associated with an increased risk of developing colon cancer. However, there is limited information on the association between family history of colorectal cancer and genetic alterations that occur in colon tumors. In this study, we evaluate the association among genetic alterations of Ki-ras and p53, microsatellite instability and having a family history of colorectal cancer in a study of incident colon cancer cases (n = 1993) and population-based controls (n = 2,410). Although there was a slight nonsignificant increase in risk of having an unstable tumor among those with a family history of colorectal cancer, this increase in risk disappeared after excluding those people with a known mutation in either of the mismatch repair genes hMLH1 or hMSH2. A family history of colorectal cancer was not associated with Ki-ras mutations overall, although those with a G to T mutation of the second base of codon 12 were more likely to have a family history of colorectal cancer than were those without this specific type of Ki-ras mutation. Cases with p53 mutations were less likely to have a family history of colorectal cancer than were cases without a p53 mutation. We believe that, given the general lack of association between having a family history of colorectal cancer and genetic alterations in tumors, these alterations are acquired through disease pathways that involve exposure from diet, lifestyle or other environmental factors.

Detection of somatic mutations of the PIG-A gene in Brazilian patients with paroxysmal nocturnal hemoglobinuria.

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired clonal syndrome characterized by intravascular hemolysis mediated by complement, thrombotic events and alterations in hematopoiesis. Basically, the molecular events which underlie the complexity of the syndrome consist of the absence of the glycosylphosphatidylinositol (GPI) anchor as a consequence of somatic mutations in the PIG-A gene, located on the X chromosome. The GPI group is responsible for the attachment of many proteins to the cytoplasmic membrane. Two of them, CD55 and CD59, have a major role in the inhibition of the action of complement on the cellular membrane of blood cells. The absence of GPI biosynthesis can lead to PNH. Since mutations in the PIG-A gene are always present in patients with PNH, the aim of this study was to characterize the mutations in the PIG-A gene in Brazilian patients. The analysis of the PIG-A gene was performed using DNA samples derived from bone marrow and peripheral blood. Conformation-sensitive gel electrophoresis was used for screening the mutation and sequencing methods were used to identify the mutations. Molecular analysis permitted the identification of three point mutations in three patients: one G-->A transition in the 5' portion of the second intron, one T-->A substitution in the second base of codon 430 (Leu430-->stop), and one deletion DeltaA in the third base of codon 63. This study represents the first description of mutations in the PIG-A gene in a Brazilian population.

A novel missense mutation C127R (FH Zagreb) in the LDL-receptor gene.

We employed the analysis of single-strand conformation polymorphisms to identify mutations in exon 4 of the low density lipoprotein receptor gene causing familial hypercholesterolemia. Three familial hypercholesterolemia heterozygotes had abnormal single-strand conformation polymorphism patterns. DNA sequencing revealed that the abnormal pattern of exon 4A was due to heterozygosity (T/C) at nucleotide 442. Nucleotide 442 is the first base of codon 127, and the T-->C mutation (C127R) changes this codon from CysTGT to ArgCGT. Abnormal patterns of exon 4B were due to heterozygosity (A/G) at nucleotide 662: nucleotide 662 is the second base of codon 200, and the A-->G mutation (D200G) changes this codon from AspGAC to GlyGGC. Mutation D200G was previously described as FH Padova, but mutation C127R (FH Zagreb) has not been reported previously. This novel mutation was confirmed by restriction endonuclease analysis with Dsa I. The screening of 420 familial hypercholesterolemia heterozygotes suggests that C127R and D200G account for about 0.7% of mutations causing familial hypercholesterolemia in Croatia.

Reassessment of K-ras mutations at codon 12 by direct PCR and sequencing from tissue microdissection in human pancreatic adenocarcinomas.

K-ras mutations at codon 12 have been detected in almost all pancreatic adenocarcinomas by highly sensitive assays. We reassessed the K-ras mutation status by direct polymerase chain reaction (PCR) and sequencing from tissue microdissection without DNA extraction in 10 pancreatic adenocarcinomas, and also assessed the K-ras and DPC4 genes in nine pancreatic cancer cell lines. Eight pancreatic adenocarcinomas were found to harbor K-ras mutations at codon 12 of either GTT or GAT, five of which were inferred to harbor amplified mutant alleles. Mutations at the sites other than codon 12 were found in seven of 70 clones (seven of 9,380 bases) by the TA cloning analysis, suggesting that artifactual mutations at the first or second base of codon 12 before and during PCR could occur at a frequency of approximately 10(-3), enough for highly sensitive assays to detect. Two cell lines without K-ras mutations at codon 12 were found to have homozygous deletions at the DPC4 gene. Thus the K-ras mutation status was demonstrated to be correctly determined by just direct sequencing from tissue microdissection. All possible mutations or multiple mutations at K-ras codon 12 that have been reported in pancreatic adenocarcinomas might include artifacts or mutations without a selective advantage. In addition, we must be very cautious about contamination.

Oculoleptomeningeal amyloidosis associated with a new transthyretin variant Ser64.

A Canadian family with oculoleptomeningeal amyloidosis with both central and peripheral nervous system disorders was described in 1988. Death of affected family members resulted from recurrent cerebral hemorrhage. To determine if oculoleptomeningeal amyloidosis is caused by a mutation in transthyretin (prealbumin). DNA isolated from peripheral blood and archival tissues of affected members of the kindred was studied by direct DNA sequencing and restriction fragment length polymorphism analysis. Direct DNA sequencing identified a thymine-to-cytosine transition at the second base of codon 64, which resulted in a replacement of serine for phenylalanine. This mutation, which creates an additional HinfI site was detected by restriction fragment length polymorphism analysis in each affected individual. In this kindred, oculoleptomeningeal amyloidosis is related to a mutation in transthyretin (Phe64Ser).

Ras gene mutations in ethmoid sinus adenocarcinoma: prognostic implications.

The presence of mutations of the 3 ras proto-oncogenes in 31 cases of ethmoid sinus adenocarcinoma, an uncommon tumor type epidemiologically related to professional exposure to wood dust, was studied. The authors studied 31 patients with ethmoid sinus adenocarcinoma. The polymerase chain reaction was used to amplify ras specific sequences of DNA isolated from paraffin embedded tumor samples. ras point mutations were subsequently detected with mutation specific oligonucleotide probes. H-ras was found to be mutated in 5 cases (16%). It is noteworthy that all of these mutations were identical and consisted of a G-for-T transversion at the second base of codon 12. H-ras mutations were related to a worse prognosis, with shorter tumor free survival (P = 0.04) and overall survival (P = 0.008). T classification was a significant clinical factor related to survival (P = 0.01 for disease free survival and P = 0.006 for overall survival). The prognostic value of H-ras mutation was consistent after adjustment for T classification. H-ras mutations showed no association with patients' previous exposure to wood dust. K-ras was found to be transformed in a single case; this was the only patient in the series to develop lymph node metastases. In this case, both the nasal tumor and the lymph nodes showed the GAT-for-GGT mutation at codon 12 of K-ras. No activation of the N-ras gene was detected. The presence of H-ras point mutations defines a subgroup of patients with ethmoid sinus adenocarcinomas for whom the prognosis is very poor. The finding that all of these mutations are identical emphasizes the peculiarity of this type of tumor.

Ras Gene mutations in ethmoid sinus adenocarcinoma

BACKGROUND The presence of mutations of the 3 ras proto-oncogenes in 31 cases of ethmoid sinus adenocarcinoma, an uncommon tumor type epidemiologically related to professional exposure to wood dust, was studied. METHODS The authors studied 31 patients with ethmoid sinus adenocarcinoma. The polymerase chain reaction was used to amplify ras specific sequences of DNA isolated from paraffin embedded tumor samples. ras point mutations were subsequently detected with mutation specific oligonucleotide probes. RESULTS H-ras was found to be mutated in 5 cases (16%). It is noteworthy that all of these mutations were identical and consisted of a G-for-T transversion at the second base of codon 12. H-ras mutations were related to a worse prognosis, with shorter tumor free survival (P = 0.04) and overall survival (P = 0.008). T classification was a significant clinical factor related to survival (P = 0.01 for disease free survival and P = 0.006 for overall survival). The prognostic value of H-ras mutation was consistent after adjustment for T classification. H-ras mutations showed no association with patients' previous exposure to wood dust. K-ras was found to be transformed in a single case; this was the only patient in the series to develop lymph node metastases. In this case, both the nasal tumor and the lymph nodes showed the GAT-for-GGT mutation at codon 12 of K-ras. No activation of the N-ras gene was detected. CONCLUSIONS The presence of H-ras point mutations defines a subgroup of patients with ethmoid sinus adenocarcinomas for whom the prognosis is very poor. The finding that all of these mutations are identical emphasizes the peculiarity of this type of tumor. Cancer 1999;86:255–64. © 1999 American Cancer Society.