Poly(ADP-ribose) polymerase and aging

The activation of oncogenes and the inactivation of tumour suppressor genes play a critical role in laryngeal tumorigenesis. Recent investigations revealed that 8p, 9p and 17q arms of human chromosomes harbour tumour suppressor genes (TSGs) such as p16 and BRCA1 with an important role in the multistage carcinogenesis of the larynx. In order to investigate the implication of these novel TSGs in the development of laryngeal neoplasia we performed a loss of heterozygosity (LOH) analysis using a bank of 15 polymorphic microsatellite markers (4 at 8p21, 7 at 9p21 arm and 4 at 17q arm surrounding the BRCA1 region) in a series of 32 cytological specimens (19 squamous cell carcinoma, 13 benign lesions of the larynx). Both benign and malignant specimens exhibited genetic alterations with at least one microsatellite marker. Fifteen (47%) out of the 32 specimens exhibited LOH at 8p21, 25/32 (78%) showed LOH at 9p21 and 18/32 (56%) displayed LOH at 17q21. Genetic alterations were detected in both benign and malignant lesions for all the loci tested suggesting an important role of these regions in the development of laryngeal neoplasia. This is the first report of detection of microsatellite alterations not only in solid tumours of the larynx but in laryngeal cytological specimens, suggesting that microsatellite analysis may be a useful tool in the primary diagnosis of the disease.     

Comment: ''devining'' the role of the consultant psychiatrist in a public mental health service

Radiographically occult bronchogenic squamous cell carcinomas are early lung cancers that localize mainly in the bronchial wall, and are thought to be a good model for investigating genetic alterations through lung cancer progression. In order to elucidate sequential genetic changes in lung cancers, we analysed the incidence of allelic losses on chromosome regions 2q33, 3p21, 5q21, 7q31, 9p21 and 17p13 for 40 cases of radiographically occult bronchogenic squamous-cell carcinomas and 40 cases of advanced lung cancers microdissected. In this study we used eight microsatellite dinucleotide polymorphic markers. Frequent loss of heterozygosity (LOH) was observed on 3p21 (53%), 5q21 (44%) and 17p13 (61%) in roentgenographically occult bronchogenic squamous cell carcinomas. 2q, 7q and 9p were lost less frequently in both roentgenographically occult bronchogenic squamous cell carcinomas and advanced lung cancers. These results suggest that several tumour-suppressor genes are associated with lung cancer progression and that genetic changes on 3p21, 5q21 and 17p13 are early events.     

Loss of heterozygosity in neuroblastomas--an overview

Although previous studies have demonstrated a relatively high incidence of loss of heterozygosity (LOH) on chromosomes 1p, 11q and 14q in neuroblastoma, it is unclear whether LOH occurs specifically on these chromosomes or not. It might be due to the lack of allelotyping of neuroblastoma. When we assessed all 22 autosomes and chromosome X for LOH in 81 cases of neuroblastoma using 43 polymorphic DNA markers, a high incidence of LOH (> 30%) was observed on three chromosomal arms, 2q (30%), 9p (36%) and 18q (31%). Moreover, 9p LOH in the tumours showed statistically significant association with advanced stage of the disease and poor prognosis. Therefore, tumour suppressor genes on chromosomes 2q, 9p and 18q could be involved in the genesis and/or progression of neuroblastoma. Particularly, the gene on chromosome 9p may be associated with progression of neuroblastoma.     

Carbohydrate-deficient glycoprotein syndrome type I: determination of the oligosaccharide structure of newly synthesized glycoproteins by analysis of calnexin binding

Familial predisposition to basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) of the skin are apparent in the autosomal dominant syndromes naevoid basal cell carcinoma syndrome (NBCCS) and multiple self-healing squamous epitheliomata (MSSE) respectively. The gene responsible for NBCCS has been proposed to be a tumour-suppressor gene and is mapped to the same 2 Mb interval on 9q22.3 as the MSSE gene ESS1. In an attempt to further map the NBCCS gene, we have examined loss of heterozygosity (LOH) in 16 sporadic BCCs and two familial BCCs using microsatellite markers located within the candidate gene region. The overall frequency of LOH observed was 67% in the BCCs and partial or interstitial deletions were found in eight tumours, with the highest LOH frequency at markers D9S280, D9S287 and D9S180. To determine if the same genomic region also shows frequent LOH in tumours with a squamous phenotype, we have examined 11 SCCs, four actinic keratoses and 13 cases of Bowen's disease for LOH at 9q22.3. An overall LOH frequency of 50% was observed at D9S180, and occurred in all types of squamous tumours. In contrast, a much lower LOH frequency of only 6% was found at the D9S287 locus. Our observation of different patterns of LOH at 9q22.3 in sporadic BCCs and SCCs implies that more than one tumour-suppressor gene might be located in this genomic region.     

Expression of two angiogenic factors, vascular endothelial growth factor and platelet-derived endothelial cell growth factor in human pancreatic cancer, and its relationship to angiogenesis

Twenty-three cases of ductal carcinoma in situ (DCIS), ten of which had an associated invasive component, were studied for loss of heterozygosity (LOH) of microsatellite markers on chromosome 9p and the results compared with a panel of 20 invasive breast carcinomas. In addition to the gene encoding p16, chromosome 9p is also thought to contain other putative tumour-suppressor genes. If the three panels of breast tumours showed LOH of markers in this region this would suggest that such putative genes were important in breast carcinogenesis. By studying both preinvasive and invasive breast tumours, it should also be possible to gain further information about the relationship between lesions of a different stage and to determine whether DCIS is indeed a precursor of invasive ductal carcinoma. Levels of LOH were low in the invasive-only set of tumours. Surprisingly, considerably higher levels of loss were observed in the tumours with an in situ component. Also, much heterogeneity was observed between different DCIS ducts or invasive tumour and DCIS from the same case.     

Comprehensive allelotyping of human hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common cancers in many parts of the world, however the molecular mechanisms underlying liver cell transformation remain obscure. A genome-wide scan of loss of heterozygosity (LOH) in tumors provides a powerful tool to search for genes involved in neoplastic processes. To identify recurrent genetic alterations in liver tumors, we examined DNAs isolated from 120 HCCs and their adjacent non tumorous parts for LOH using a collection of 195 microsatellite markers located roughly every 20 cM throughout 39 autosomal arms. The mean heterozygosity was 73%. Our findings provide additional support that LOH for loci on chromosomal arms 1p, 4q, 6q, 8p, 13q and 16p is significantly elevated in HCC. The highest percentage of LOH is found for a locus in 8p23 (42% of informative csaes). This corresponds to one of the most common genetic abnormalities reported to date in these tumors. In addition, high ratio of LOH (> or = 35%) is observed on chromosome arms which had not been implicated in previous studies, notably on 1q, 2q and 9q. No correlation was found between LOH of specific chromosomal regions and etiologic factors such as chronic infections with hepatitis B or C viruses. This first report of an extensive allelotypic analysis of HCC should help in identifying new genes whose loss of function contributes to the development of liver cancer.     

Allelotype and replication error phenotype of small cell lung carcinoma

Allelotype and replication error (RER) phenotype analyses were performed to clarify the pathogenetic significance of inactivation of tumor suppressor genes and genomic instability in the genesis and progression of small cell lung carcinoma (SCLC). We examined 37 cases of SCLC for loss of heterozygosity (LOH) and microsatellite instability at 49 loci on all 39 nonacrocentric chromosomal arms. LOH was frequently (>70%) detected on chromosomes 3p (29/32, 90.6%), 5q (15/21, 71.4%), 13q (25/26, 96.2%), 17p (22/25, 88.0%), and 22q (24/33, 72.7%). Frequent LOH (>70%) on these loci was observed even among seven cases of stage I tumors. The incidence of LOH on all 39 nonacrocentric chromosomal arms was not significantly different between primary tumors and metastases. These results suggest that inactivation of multiple tumor suppressor genes accumulates relatively early during progression of SCLC and it may be responsible for clinically and biologically aggressive phenotype of SCLC. RER was observed in 6/37 (16.2%) of SCLC, however, RER at multiple loci was observed only in two cases. Therefore, it was indicated that genomic instability is uncommon, but might play a role in the genesis of a small subset of SCLC.     

Evidence for loss of heterozygosity in human psoriatic lesions

Psoriasis, a disease of human skin, is characterized by abnormal differentiation and hyperproliferation of keratinocytes; it has a genetic background. Using 11 highly polymorphic microsatellite markers on eight chromosome arms, we performed an allelotype analysis in 14 psoriatic plaques, in order to reveal any chromosome deletions involved in the development of the disease. We detected loss of heterozygosity (LOH) on at least one microsatellite marker in nine of 14 (64%) cases. We also observed particular genetic loci altered with LOH, on chromosomes 3p, 7p/q and 8p. Our results suggest that LOH is an important phenomenon in the development of psoriatic plaques, providing evidence for deletion of regulatory genes.     

Ethnic differences in interferon-alpha allele frequencies

We analyzed microsatellite instability (MSI) and loss of heterozygosity (LOH) at 17 microsatellite markers located on chromosomes 2p, 3p, 5q, 6q, 9p, 9q, 17p and 18q in 19 randomly selected keratoacantomas (KAS), in one cutaneous lesion that histologically could not unequivocally be differentiated from squamous cell carcinoma, and in one patient with multiple KAs of longstanding duration. The goals of our study were to determine whether, in a similar manner to some visceral carcinomas, genomic instability could be detected in KAs and to clarify whether molecular analysis might be useful to further characterize KA. MSI was observed in 2 of 21 cases (9.5%) at 5 of 17 loci examined. In one patient with a solitary KA, the presence of MSI and a family history of visceral malignant tumours suggested that the patient might have belonged to a family with Muir-Torre syndrome. In one other MSI+ KA, a definite differential diagnosis in relation to squamous cell carcinoma could not be established. In addition, one sample displayed LOH at 2 of 17 loci analysed whereas in the patient with multiple KAs, LOH at one locus was the only alteration found. In conclusion, the low frequency of MSI and LOH detected in our study suggests that these genetic events are uncommon in KA unless it is associated with a familial disease (e.g. Muir-Torre syndrome) or it has more aggressive histological features.     

A case of double primary adenocarcinoma of the lung with multiple atypical adenomatous hyperplasia

A case of double primary adenocarcinoma of the lung with multiple atypical adenomatous hyperplasia (AAH) in a 77-year-old woman is reported. Histopathologically, in the resected left upper lobe of the lung, both cancers were diagnosed as well-differentiated papillary adenocarcinoma, and 161 lesions of AAH were also found. Both the cancer lesions and six AAH (greater than 3 mm in diameter) were examined with regard to immunoreactivity of carcinoembryonic antigen (CEA) and p53 gene product, microsatellite instability (MI) and loss of heterozygosity (LOH) on chromosome 9q and 17q by polymerase chain reaction (PCR). Although both cancers expressed CEA, they did not show clonal immunoreactivity for the p53 gene product. Atypical adenomatous hyperplasia expressed CEA weakly and showed no immunoreactivity for p53 gene protein. Both carcinomas showed LOH on chromosome 17q, and one of them showed LOH on chromosome 9q. In six AAH, LOH on chromosome 17q was detected in two tumors, and one of them also showed LOH on chromosome 9q. One AAH, which was negative for LOH on chromosome 17q and 9q, showed MI at D17S791. These results indicated that AAH is a clonal neoplastic lesion with genetic abnormalities and should be called intraepithelial pneumocyte neoplasia, and that each of the numerous papillary lesions in this case was considered to be an independent lesion.     

Reduced exploratory activity of audiogenic seizures susceptible Wistar rats

To search for the existence of a tumour-suppressor gene (TSG) associated with oral squamous cell carcinoma (SCC), PCR analysis of microsatellite polymorphisms corresponding to 14 loci which map to chromosome 7q21.3-qter was performed to screen 35 patients with oral SCC for loss of heterozygosity (LOH). LOH was observed in at least one of the loci in 19 of 34 (55.9%) informative cases. Among the loci tested, frequent LOH was restricted at D7S522 on chromosome 7q31.1, which was measured within 1 cM. Furthermore, we detected microsatellite instability (MI) in 11 of 35 (31.4%) cases tested. Our observations indicate that alterations of chromosome 7q are associated with oral SCC tumorigenesis and that 7q31.1 might harbour at least one putative TSG.     

Loss of heterozygosity at chromosome 6q in preinvasive and early invasive breast carcinomas

We have used polymerase chain reaction (PCR) analysis to study the incidence of allelic imbalance at four polymorphic microsatellite markers on chromosome 6q25.1-27, three dinucleotide repeats and one trinucleotide repeat, for microdissected tumour foci from a group of 75 'early' breast carcinomas. The tumours comprised 16 preinvasive cases of ductal carcinoma in situ (DCIS) and 59 mammographically detected early invasive carcinomas. Loss of heterozygosity (LOH) was detected at all four loci and in all types and grade of disease. The frequency of LOH ranged from 23% to 50% depending on the marker studied. The highest frequency of LOH was observed at the D6S186 locus for the cases of DCIS and at the oestrogen receptor locus for the invasive carcinomas. These data suggest that the inactivation of tumour-suppressor genes within this region on chromosome 6q is important for the development of these early lesions.     

Monitoring of proteinuria in phase I studies in healthy male subjects

An extended analysis for loss of heterozygosity (LOH) on eight chromosomes was conducted in a series of 82 Wilms tumors. Observed rates of allele loss were: 9.5% (1p), 5% (4q), 6% (6p), 3% (7p), 9.8% (11q), 28% (11p15), 13.4% (16q), 8.8% (18p), and 13.8% (22q). Known regions of frequent allele loss on chromosome arms 1p, 11p15, and 16q were analyzed with a series of markers, but their size could not be narrowed down to smaller intervals, making any positional cloning effort difficult. In contrast to most previous studies, several tumors exhibited allele loss for multiple chromosomes, suggesting an important role for genome instability in a subset of tumors. Comparison with clinical data revealed a possible prognostic significance, especially for LOH on chromosome arms 11q and 22q with high frequencies of anaplastic tumors, tumor recurrence, and fatal outcome. Similarly, LOH 16q was associated with anaplastic and recurrent tumors. These markers may be helpful in the future for selecting high-risk tumors for modified therapeutic regimens.     

Molecular analysis of childhood primitive neuroectodermal tumors defines markers associated with poor outcome

PURPOSE: The diagnostic and prognostic significance of well-defined molecular markers was investigated in childhood primitive neuroectodermal tumors (PNET). MATERIALS AND METHODS: Using microsatellite analysis, Southern blot analysis, and fluorescence in situ hybridization (FISH), 30 primary tumors and six CSF metastasis specimens were analyzed for loss of heterozygosity (LOH) of chromosomes 1q31, 6q, 9q22, 10q, 11, 16q22, and 17p13.1 and/or high-level amplification of the c-myc gene. Experimental data were compared with clinical stage and outcome. RESULTS: LOH of chromosome 17p13.1 was found most frequently (14 of 30 tumors, six of six CSF metastasis specimens); LOH of chromosomes 10q, 16q22, 11, 6, 9q22, and 1q31 was observed in 20.6%, 20%, 14.3%, 12%, 10%, and 0%, respectively. Eight of 32 tumors and CSF specimens showed amplification of c-myc. All tumors with amplification of c-myc were resistant to therapy and had a fatal outcome (mean survival time, 9.3 months). Tumors that displayed LOH of chromosome 17p were associated with metastatic disease. The prognosis of these tumors was worse only when associated with amplification of c-myc. Three of three patients with LOH of 9q22 relapsed. CONCLUSION: In our study, amplification of c-myc was a poor-prognosis marker in PNET. LOH of chromosome 17p was associated with metastatic disease. Molecular analysis of primary tumors using these markers may be useful for stratification of children with PNET in future prospective studies. The other aberrations investigated were not of significant prognostic value, but may provide an entry point for future large-scale molecular studies.     

Molecular damage in the bronchial epithelium of current and former smokers

BACKGROUND: Most lung cancers are attributed to smoking. These cancers have been associated with multiple genetic alterations and with the presence of preneoplastic bronchial lesions. In view of such associations, we evaluated the status of specific chromosomal loci in histologically normal and abnormal bronchial biopsy specimens from current and former smokers and specimens from nonsmokers. METHODS: Multiple biopsy specimens were obtained from 18 current smokers, 24 former smokers, and 21 nonsmokers. Polymerase chain reaction-based assays involving 15 polymorphic microsatellite DNA markers were used to examine eight chromosomal regions for genetic changes (loss of heterozygosity [LOH] and microsatellite alterations). RESULTS: LOH and microsatellite alterations were observed in biopsy specimens from both current and former smokers, but no statistically significant differences were observed between the two groups. Among individuals with a history of smoking, 86% demonstrated LOH in one or more biopsy specimens, and 24% showed LOH in all biopsy specimens. About half of the histologically normal specimens from smokers showed LOH, but the frequency of LOH and the severity of histologic change did not correspond until the carcinoma in situ stage. A subset of biopsy specimens from smokers that exhibited either normal or preneoplastic histology showed LOH at multiple chromosomal sites, a phenomenon frequently observed in carcinoma in situ and invasive cancer. LOH on chromosomes 3p and 9p was more frequent than LOH on chromosomes 5q, 17p (17p13; TP53 gene), and 13q (13q14; retinoblastoma gene). Microsatellite alterations were detected in 64% of the smokers. No genetic alterations were detected in nonsmokers. CONCLUSIONS: Genetic changes similar to those found in lung cancers can be detected in the nonmalignant bronchial epithelium of current and former smokers and may persist for many years after smoking cessation.     

Multifocal renal cell carcinoma: evidence for a common clonal origin

The reported incidence of satellite tumor lesions in kidneys resected by radical nephrectomy for renal cell carcinoma (RCC) is 7-25%; however, genetic analyses of satellite tumors in comparison with those of main tumor lesions have not been performed well. In the present study, we investigated the incidence of loss of heterozygosity (LOH) at chromosome arms 3p, 6q, 8p, 9p, 9q, and 14q using 18 microsatellite markers in 10 nonpapillary RCCs of 50 mm or less in diameter and the accompanying satellite tumor lesions to evaluate the genetic alterations in main and satellite tumors. LOH was detected in 10, 3, 5, 3, 2, and 3 cases at chromosome arms 3p, 6q, 8p, 9p, 9q, and 14q, respectively. In addition, primary and satellite tumor lesions in 8 of 10 cases exhibited identical patterns of LOH on the 18 loci examined. In the remaining two cases, both main and satellite tumors demonstrated LOH on the common seven and three loci, respectively, whereas for another locus, LOH was observed only in the satellite tumor lesions. The similarity of LOH patterns detected in main and satellite tumor lesions indicates that the presence of satellite tumors might be the result of intrarenal metastasis from the main tumor lesion. These findings strongly suggest that even in case of small nonpapillary RCC, nephron-sparing surgery might carry the risk of failing to prevent postoperative local recurrence due to the incomplete resection of unrecognized satellite tumors with genetic alterations similar to those of the main tumor.     

Loss of heterozygosity of BRCA1, TP53 and TCRD markers analysed in sporadic endometrial cancer

Genetic alterations of tumour suppressor genes, for which loss of heterozygosity (LOH) is one mechanism of gene inactivation, are important steps in the development of endometrial cancer. To investigate the clinical relevance of LOH of BRCA1 (17q21), TP53 (17p13) and TCRD (14q11) in endometrial cancer, polymerase chain reaction (PCR)-based fluorescent DNA technology for the detection of microsatellite polymorphisms was applied. One hundred and thirteen archival endometrial cancer samples with matched normal tissues were examined. Allele loss at three loci were correlated with age, tumour size, lymph node status, metastases, stage, histological types, grade, expression of oestrogen receptor (ER) and progesterone receptor (PgR), family history of cancer, previous history of cancer or precursor lesions, and previous history of hormone replacement therapy (HRT). LOH for BRCA1 was detected in 18.1%, of TP53 in 26.9%, and of TCRD in 26.3% of informative cases. LOH of BRCA1 correlated with medium grade, positive ER status, and family history of cancer; LOH of TP53 correlated with younger age, high grade, positive PgR status, and with tumours from patients without HRT; LOH of TCRD correlated only with family history of cancer. LOH at all three loci correlated only with grade and positive family history. Allele loss of one of the three tumour suppressor loci did not correlate with disease-free survival (DFS), but LOH of BRCA1 correlated significantly with decreased overall survival (OS). The latter, together with the correlation of LOH of BRCA1 locus with steroid hormone receptor expression, might give a hint to the potential involvement of the co-localised 17 beta-hydroxysteroid dehydrogenase (HSD) gene in the development of endometrial cancer.     

Pathogenesis of adenocarcinoma in Peutz-Jeghers syndrome

Peutz-Jeghers syndrome (PJS) is an autosomal dominant condition characterized by intestinal hamartomatous polyps, mucocutaneous melanin deposition, and increased risk of cancer. Families with PJS from the Johns Hopkins Polyposis Registry were studied to identify the molecular basis of this syndrome and to characterize the pathogenesis of gastrointestinal hamartomas and adenocarcinomas in PJS patients. Linkage analysis in the family originally described by Jeghers in 1949 and five other families confirmed linkage to 19p13.3 near a recently identified gene responsible for PJS. Germ-line mutations in this gene, STK11, were identified in all six families by sequencing genomic DNA. Analysis of hamartomas and adenocarcinomas from patients with PJS identified loss of heterozygosity (LOH) of 19p markers near STK11 in 70% of tumors. Haplotype analysis indicated that the retained allele carried a germ-line mutation, confirming that STK11 is a tumor suppressor gene. LOH of 17p and 18q was identified in an adenocarcinoma but not in hamartomas, implying that allelic loss of these two regions corresponds to late molecular events in the pathogenesis of cancer in PJS. The adenocarcinomas showing 17p LOH also demonstrated altered p53 by immunohistochemistry. None of the 18 PJS tumors showed microsatellite instability, LOH on 5q near APC, or mutations in codons 12 or 13 of the K-ras proto-oncogene. These data provide evidence that STK11 is a tumor suppressor gene that acts as an early gatekeeper regulating the development of hamartomas in PJS and suggest that hamartomas may be pathogenetic precursors of adenocarcinoma. Additional somatic mutational events underlie the progression of hamartomas to adenocarcinomas, and some of these somatic mutations are common to the later stages of tumor progression seen in the majority of colorectal carcinomas.     

Human bladder cancers and normal bladder mucosa present the same hot spot of heterozygous chromosome-9 deletion

Loss of heterozygosity (LOH) on chromosome 9 is the most frequent genetic alteration in bladder cancer identified to date, suggesting the presence of key gene(s) for this pathology. In this study, we examined 44 bladder tumors and 21 normal bladder samples for LOH on both arms of chromosome 9. Sixteen microsatellite markers, 12 on the short arm (encompassing 9p21-22) and 4 on the long arm (encompassing 9q33-34), were chosen for their highly frequent alterations in bladder cancer. LOH for at least one marker was identified in 42 tumor samples (95.5%), and 14 tumors (32%) displayed LOH for all informative tested markers. Detailed analysis showed that 2 markers on chromosome 9p (D9S157 and D9S156) had the highest frequencies of allelic loss (about 70%), independent of tumor grade and stage. The same study was performed on the 21 normal bladder mucosa samples: 50% of informative cases presented a single specific LOH at the D9S156 locus. Normal samples showing LOH at this locus were therefore screened with 3 novel microsatellite markers in the 810-kb region incorporating D9S156. Using this marker, we found no further heterozygous loss in this region. This result allows different interpretations of the D9S156 loss in normal bladder mucosa, and suggests that D9S156 may be more an indicator of bladder epithelium impairment than a tumor-initiation marker. Similarly, this unexpected result calls in question the interpretation of LOH studies.     

Molecular genetic evidence for the conversion hypothesis of the origin of malignant mixed müllerian tumours

The origin of malignant mixed Müllerian tumours (MMMTs) has long been debated, due to the indefinite relationship between epithelial and mesenchymal malignant cells. In order to obtain insight into the clonal relationship between the two components of these tumours, molecular genetic changes were investigated at the level of loss of heterozygosity (LOH) in both cells types. LOH was studied in a series of six cases with 74 polymorphic microsatellite markers mapping to 19 different chromosomes. The epithelial and the mesenchymal neoplastic cells were separately microdissected from formalin-fixed, paraffin-embedded tissue, prior to DNA isolation. LOH was observed for 35 different markers mapping to chromosomes 3, 6, 8, 11, 15, 16, 17, 18, 21, and X. The most frequently involved chromosomes were 17p, 17q, 11q, 15q, and 21q. LOH was observed in five out of six cases and identical alleles were lost in the epithelial and in the mesenchymal cells. No genetic differences were observed between the two cell types for any of the informative markers. Immunohistochemistry (IHC) and TP53 mutation analysis revealed involvement of TP53 in all cases. Mutations were identified in five MMMTs. In four tumours, of which three had a missense mutation, strong nuclear staining for p53 was observed. In the remaining two cases, the mutation resulted in a stop codon, with no nuclear staining for p53 by IHC. The results support a monoclonal origin of MMMTs, with the absence of genetic changes uniquely associated with either of the phenotypes. The latter finding is compatible with current opinion that these neoplasms should be considered as metaplastic carcinomas and supports the conversion hypothesis.