Molecular and immunohistochemical analysis of p53 mutations in scrapings and tissue from preinvasive and invasive breast cancer

 Mutations of the p53 gene appear to be one of the most common abnormalities in human cancer. Although many studies have been published about p53 alterations in breast cancer, data on molecular biological detection of p53 mutations in in situ lesions are still rare, and the implications for breast cancerogenesis are unclear. Tissue samples from 83 patients with different stages of breast cancer and from 13 patients with benign breast lesions were screened for p53 gene mutations by polymerase chain reaction (PCR) followed by temperature-gradient gel electrophoresis (TGGE). p53 protein accumulation was analysed by immunohistochemistry (IHC). Samples were gained from fresh-frozen tissue, scrapings, or paraffin embedded tissue. Additionally, 23 pairs of primary tumours and corresponding lymph nodes were examined. p53 gene aberrations were found in 55.7% of the infiltrating carcinomas, in 31.5% of the ductal carcinomas in situ (DCIS) and in one atypical ductal hyperplasia. A positive correlation was seen with high-grade tumours and with comedo. There was no statistically significant relationship with respect to age, menopausal status, tumour size, hormone receptor status or lymphatic invasion. Concordance between TGGE and IHC was seen in only 63% of the cases analysed. However, with regard to p53 mutation screening by TGGE, a high significance (P = 0.0008) was seen between standard tissue extraction and our scrape preparation technique. Among 8 pairs of primary tumours and their corresponding lymph node metastases, only 3 harbored identical p53 mutations in the same exon, while in 5 cases with mutant p53 in the primaries, no mutation was seen in the lymph node. Our data indicate that p53 mutations are frequent in breast tumours associated with unfavorable prognosis, including high-grade or the comedo histotype. There is evidence that p53 gene alterations occur early in breast cancerogenesis, as mutations were detected not only in in situ carcinomas but also in atypical ductal hyperplasia. Received: 14 April 1997 / Accepted 20 May 1997     

Expression of E-cadherin and its relation to the p53 protein status in human breast carcinomas

 In breast carcinomas the TP53 gene is altered in 10–30% of cases. Alteration of the gene may lead to a general genomic instability, detected as deletions and/or amplifications at the gene level, and as altered expression at the mRNA and protein level. We have demonstrated a strong association between down-regulation of E-cadherin protein expression and alterations of the p53 protein, detected as TP53 gene mutation and/or protein accumulation in tumour samples from 210 patients with breast carcinomas (P <0.001). Investigation of allelic imbalance using microsatellite markers located near the E-cadherin locus was also performed. A higher frequency of loss of heterozygosity in the microsatellite marker closest to the E-cadherin locus was observed in samples with down-regulation of E-cadherin protein expression. A higher frequency of down-regulation of the E-cadherin protein expression was found in invasive lobular carcinomas than in invasive ductal carcinomas, although this difference was of borderline significant (P=0.084). Cases in the present series were also immunostained for c-erbB-2 protein overexpression. A significant association between p53 protein accumulation and cerbB-2 protein overexpression was seen (P=0.036). The results of the present study indicate that p53 protein may play a role in regulation of E-cadherin protein expression. Received: 29 May 1997)Accepted: 10 June 1997     

p21WAF1/CIP1 expression in colorectal carcinoma correlates with advanced disease stage and p53 mutations

Defects in the mechanisms controlling the cell cycle are crucial in cell transformation and/or tumour progression. p21^WAF1/CIP1 is an inhibitor of cyclin-dependent kinases, induced by p53-dependent and p53-independent pathways, which can block progression through the cell cycle. p21^WAF1/CIP1 expression has been investigated immunohistochemically in a series of 191 patients with colorectal cancer of known p53 status. The purpose of the study was two-fold: to assess the relationship between p21^WAF1/CIP1 immunoreactivity and p53 alterations, and to evaluate the prognostic significance of p21^WAF1/CIP1 expression. In 96 carcinomas (51 per cent), p21^WAF1/CIP1 was expressed in over 10 per cent of tumour cells, whereas in 26, p21^WAF1/CIP1 was detected in under 10 per cent of neoplastic cells; 69 tumours lacked p21^WAF1/CIP1 expression. Immunoreactivity was more frequent in tumours of the right colon (p < 0·003) and was inversely correlated with tumour stage (p < 0·03), p53 gene mutations (p < 0·0007), p53 protein accumulation (p < 0·019), and Bcl-2 expression (p < 0·0005). In univariate analysis, down-regulation of p21^WAF1/CIP1 expression was associated with poor overall (p = 0·0022) and disease-free survival (p = 0·0009). Multivariate analysis, however, did not confirm any independent prognostic significance of p21^WAF1/CIP1 expression. The results indicate that p21^WAF1/CIP1 is associated with abnormal accumulation of p53 protein and the occurrence of p53 gene mutations in colorectal cancer and that lack of p21^WAF1/CIP1 expression is correlated with reduced patient survival in univariate analysis. These data underline the crucial pathogenetic role of the p53–p21^WAF1/CIP1 pathway in carcinomas of the large bowel. Copyright © 1999 John Wiley & Sons, Ltd.     

Expression of p53 protein in infiltrating and in-situ breast carcinomas.

Five antibodies directed against the whole or part of p53 protein have been used to detect the protein immunohistochemically in 70 infiltrating breast carcinomas and 10 ductal carcinomas in situ. Mutations are known to occur in different conserved domains, and the antibodies employed spanned the expected sites. p53 protein was identified in 53 per cent of infiltrating carcinomas using the antibodies PAb 240, PAb 1801, C19, and JG8. The antibody PAb 421 detected the protein in 31.5 per cent; all positive with the other antibodies. Well-differentiated oestrogen receptor-positive tumours had a low incidence of p53 detection. Variation in the percentage of reactivity was seen between carcinomas and in some cases between different antibodies in the same cancer. Those carcinomas with a high percentage of positive cells with all antibodies were more likely to have metastasized to nodes, be at an advanced stage, and be oestrogen receptor-negative/epidermal growth factor receptor-positive. There was no significant correlation with c-erbB-2 protein expression or retinoblastoma protein loss. p53 protein was detected in a high proportion of cells in three of the six comedo ductal carcinomas in situ studied but either not at all or at a lower level in tumours of the cribriform type. p53 mutations are common in breast carcinomas, but heterogeneity within individual tumours is frequent. Marked expression of p53 appears to relate to tumour progression.     

p53 expression in CMV-infected cells: association with the alternative expression of the p53 transactivated genes p21/WAF1 and MDM2

The p53 tumour suppressor gene is a cell cycle regulator, able to induce cell cycle arrest to allow DNA repair or apoptosis. The molecular mechanisms underlying p53 action imply transactivation of p53 dependent genes such as WAF1 (for wild type p53 associated fragment 1) and the murine double minute (MDM2) gene. In some cases, inactivation of the p53 gene results from p53 gene mutations leading to p53 protein accumulation, but in others it may results from mechanisms other than mutation, such as interaction with viral or cellular proteins. The expression of p53 protein and p53 transactivated gene proteins p21/WAF1 and MDM2, combined with in situ detection of apoptosis, was studied in specimens of CMV-infected patients as an in vivo model of p53 alteration not due to point mutation. p53 positivity was found in CMV + cells in different tissues, in cells with typical inclusion bodies, and in in situ hybridization and immunohistochemistry CMV + cells without inclusions (hidden infection). Although this p53 reactivity was accompanied by the expression of MDM2 and p21/WAF1 proteins, the patterns of MDM2 and p21/WAF1 protein expression were mutually exclusive, and were associated with the presence or absence of inclusion bodies. Nuclei bearing inclusion bodies were usually MDM2 +, p21/WAF1?, while hidden infected cells were usually MDM2?, p21/WAF1 +. Apoptosis was not detected in any tissue section from CMV-infected patients. Two alternative patterns were found in CMV-infected tissues: p53 +, p21/WAF1 +, MDM2?, or p53 +, p21/WAF1?, MDM2 + protein expression. These may represent examples of p53 dependent alternative effects in the course of CMV infection. Early stages are represented by CMV + cells without inclusion bodies, which display p53 and p21/WAF1 expression, suggesting that p53 could be acting as a growth suppressor protein. Late CMV infection is represented by cells harbouring inclusion bodies. These cells showed a p53 +, p21/WAF1?, MDM2 + profile, consistent with MDM2 mediated p53 inactivation. The absence of p21/WAF1 expression and lack of apoptosis suggest that the p53 protein expressed by MDM2 + cells could be functionally inactivated in CMV-infected cells with inclusion bodies. Previous studies have suggested that p53 inactivation by MDM2 over-expression occurs in sarcomas and lymphomas. Our observations seem to indicate that this mechanism of MDM2 mediated p53 inactivation may play a role in the late phase of CMV infection.     

p21 Expression in colorectal carcinomas: a study on 103 cases with analysis of p53 gene mutation/expression and clinic-pathological correlations

The WAF1/CIP1 gene product, p21, an inhibitor of cyclin-dependent kinases, is a critical downstream effector in the p53 pathway. The expression of p21 in human neoplasms is heterogeneous, and may be related to p53 functional status. We evaluated p21 immunoreactivity in 103 colorectal carcinomas (CC) in relation to the p53 gene and protein alterations and clinico-pathologic parameters. High p21 expression (more than 10% reactive cells) was seen in 39% of cases. p21 staining was heterogeneous and often detected in clusters of tumour cells; in some tumours p21 staining was more pronounced in superficial areas. No relation was seen between p21 immunoreactivity and site of the tumours (right vs left), TNM stage and grade. p21 expression was related to p53 status as evaluated with IHC or with SSCP analyses, low p21 expression usually being associated with p53 protein overexpression (P=0.048) and p53 gene alteration (P=0.005). The strongest associations were seen when the combined p53/p21 immunophenotype was compared with p53 gene alterations (P=0.0002). These data support the hypothesis that p21 expression in CC is mainly related to p53 functional status, suggesting that p21 expression could be an interesting adjunct in the evaluation of the functional status of the p53 pathway in CC. Received: 22 February 1999 / Accepted: 21 June 1999     

p21WAF1/Cip1 expression is associated with cell differentiation but not with p53 mutations in squamous cell carcinomas of the larynx

p21^WAF1/Cip1 is a recently identified gene involved in cell cycle regulation through cyclin-CDK-complex inhibition. The expression of this gene in several cell lines seems to be induced by wild-type, but not mutant, p53. p21^WAF1/Cip1 expression has been studied at both mRNA and protein levels in a series of 49 normal mucosae and squamous cell carcinomas of the larynx. A significant association was found between mRNA and protein expression in tumours (P<0·0001). p21^WAF1/Cip1 expression was strongly associated with squamous cell differentiation of carcinomas, because six of seven (86 per cent) undifferentiated carcinomas (grade 4) showed very low levels of p21^WAF1/Cip1 expression, whereas 41 out of 42 (98 per cent) carcinomas with squamous cell differentiation (grades 1–3) had normal or high levels of p21^WAF1/Cip1 expression (P<0·0001). In addition, p21^WAF1/Cip1 expression was topologically related to the squamous differentiation of tumour cells with a distribution similar to that seen in normal squamous epithelium. No correlation was found between p21^WAF1/Cip1 expression and the global S-phase of the carcinomas. p53 mutations (exons 5–9) were found in ten carcinomas with p21^WAF1/Cip1 expression, but no p53 mutations were detected in three p21^WAF1/Cip1-negative tumours. In conclusion, p21^WAF1/Cip1 expression is frequently upregulated in squamous cell carcinomas of the larynx and is associated with tumour cell differentiation. p21^WAF1/Cip1 expression in these tumours is independent of p53 gene mutations. © 1997 John Wiley & Sons, Ltd.     

大肠癌组织p14ARF与p53基因变异研究

目的：观察大肠癌组织p14ARF基因遗 传和表观遗传变化及p53基因突变状况，探讨两者改变的关系及p14ARF-p53通路功能 破坏在大肠癌发生中的作用。方法：应用PCR、直接测序、甲基化特异PC R和RT-PCR分别检测56例原发性大肠癌及相应癌旁正常组织p14ARF基因纯合性缺失、 突变、5′CpG岛甲基化、mRNA表达及p53基因突变状况。结果：①大肠 癌组织p14ARF总变异率为27% (15/56)，其中1例纯合性缺失，14例5′CpG岛甲基化,未见突变发生。②15例p14ARF基因变异的大肠癌组织其相应mRNA表达阴性（13例）或 低水平表达（2例），41例未发生基因变异的大肠癌组织和所有癌旁正常组织p14ARF mRNA均显示明显表达。③大肠癌组织p53突变率为48% (27/56)。④56例大肠癌组织中，12例 仅发生p14ARF变异，24例仅显示p53突变，3例同时有p14ARF 5′CpG岛甲基化 和p53突变，17例p14ARF和p53均无变异，p14ARF-p53通路总变异率为70%（39/ 56），p14ARF 5′CpG岛高甲基化与野生型p53状态有关（P＜0.05）。⑤低分化 腺癌组p14ARF变异率（44%，7/16）明显高于高中分化腺癌组（20%，8/40）（P＜ 0.05），但两组间p53突变率无显著差异（P＞0.05）。结论:①大肠癌p14ARF基因5′ CpG岛高甲基化是其表达失活的主要机制；②大肠癌p14 ARF基因高甲基化与p53基因突变可能是相互独立的事件，两者的失活可能各自出现于不同 的大肠癌亚组中；③p14ARF高甲基化或p53突变引起的p14ARF-p53通路功能 破坏在大肠癌的发生中具有重要作用。     

Prognostic significance of p53 gene mutations and p53 protein expression in synovial sarcomas

Alterations to p53 seem to be of prognostic significance in soft tissue sarcomas, but their significance for synovial sarcomas has not been studied. We analysed 34 synovial sarcomas in 19 patients for p53 alterations (p53 gene mutations + p53 immunopositivity) and examined this factor for its prognostic value in a group of 15 primary tumours. DNA was prepared from paraffin-embedded tumour material by a modified proteinase K/phenol/chloroform extraction. p53 gene mutations of exons 5–8 were analysed by the PCR-SSCP-sequencing method. p53 protein expression was evaluated by immunohistochemistry using the murine monoclonal antibody DO1. We found two missense mutations (5.9%) and ten p53 immunopositive cases (29.4%). Both tumours with p53 mutations showed p53 protein expression. There was no significant correlation between p53 alteration and histological subtype, age, sex, or tumour size. The 5-year survival rate was 24.1%. Overall survival was significantly reduced in patients having synovial sarcomas with p53 alterations (P<0.001). In the multivariate Cox’s analysis, only p53 alterations (P=0.032) and tumour size (P=0.023) emerged as independent prognostic factors. We suggest that p53 alterations may be a useful prognostic indicator in synovial sarcomas, allowing rational clinical treatment and follow-up. Received: 13 April 1999 / Accepted:18 May 1999     

Comparison of benign and malignant endometrial lesions for their p53 state, using immunohistochemistry and temperature-gradient gel electrophoresis

The aim of this study was to evaluate the presence and distribution of p53 alterations in pure endometrioid adenocarcinomas (n=120) of different grades and stages, as opposed to normal endometrium (n=13) and various risk groups of hyperplasia (n=39). All samples were initially analysed by immunohistochemistry with the monoclonal antibody Ab-6. Normal endometria were negative. With increasing degrees of malignancy, the number of cases with p53 accumulation rose and ranged from 9% to 18% in hyperplasia, through 25% in lowgrade carcinomas (G1), to 69% in high-grade carcinomas (G3). This increase was also seen when comparing tumours by stage. Of carcinomas in stage IA, only 17% showed p53 immunostaining, in contrast with 72% in stage IC. Of this material, 34 carcinomas and 8 hyperplasias were analysed for p53 mutations in exons 5–8 by means of polymerase chain reaction and temperature-gradient gel electrophoresis (TGGE). In none of 5 hyperplasia and 6 of 12 carcinomas showing p53 accumulation by immunohistochemistry, p53 mutations were detected by TGGE. In contrast, 4 of 22 carcinomas harboured mutant p53 but were negative by immunohistochemistry. Immunohistochemical and molecular investigations revealed that p53 alterations are related to the standard prognostic markers of endometrial cancer, i.e. grading and staging. TGGE, an indirect screening procedure for p53 mutations, is used to detect the type of p53 alteration and may provide additional insight into the complex figure of p53 abnormalities in the development and progression of malignant endometrial lesions.     

p53 Alterations in thymic epithelial tumours

 The prognosis of thymic epithelial tumours depends on malignant behaviour that cannot always be predicted on histological grounds. This study aimed at identifying a molecular marker that would be useful in overcoming the drawbacks of histopathology. Forty-four thymic epithelial tumours were analysed for alterations of the tumour suppressor gene p53 using immunohistochemistry (antibodies D0-1 and CM-1) and PCR-based single-strand conformation polymorphism and DNA sequencing. Histological and clinical evaluation and also p53 analysis revealed three major tumour groups: non-organotypic thymic carcinomas with frequent p53 alterations (7/9) and occurrence of p53 gene mutations (2/9); malignant thymomas with frequent p53 alterations but without p53 gene mutations (11/18); and benign thymomas with rare p53 alterations and without p53 gene mutations (2/17). In non-organotypic thymic carcinomas p53 was detected with both antibodies. In contrast, thymomas lacked immunoreaction with D0-1 suggesting alteration of the antibody-binding site. Overall immunohistochemical results correlated with clinical stages (P < 0.01), pathohistology (P < 0.01), and survival times (P < 0.05). We consider immunohistochemical p53 detection to be a useful new prognostic factor for the evaluation of thymic epithelial tumours. Received: 5 September 1996 / Accepted: 17 February 1997     

Molecular analysis of p53 gene in laryngeal premalignant and malignant lesions. p53 protein immunohistochemical expression is positively related to proliferating cell nuclear antigen labelling index

This study was undertaken in order to investigate the molecular nature of the p53 gene in 19 laryngeal squamous cell carcinomas and dysplasias. Moreover, we have examined the possible relationship between proliferating cell nuclear antigen (PCNA) expression and p53 protein detection status in 42 laryngeal premalignant and malignant lesions in which 14 of the 19 samples used in the molecular study were included. p53 gene analysis was performed with the single-strand conformation polymorphism technique. PCNA was stained with the peroxidase/antiperoxidase immunohistochemical method using the monoclonal antibody PC-10. Data from previous work concerning p53 expression was used. We found that 9 of 12 of the immunohistochemically p53 positive (+) cases had mutations in exons 5 or 6. In the remaining immunohistochemically p53(+) and p53 negative (–) specimens there was no indication of sequence alterations. Furthermore, we did not observe any deletions in the chromosomal region 17p31.1 which encodes exons 4–8 of the p53 gene. The PCNA labelling index (LI) increased progressively with p53 protein detection status (percentage of cells immunohistochemically positive for p53). The difference between the group with the higher percentage of p53(+) cells and the others was statistically significant. These data show that although there is a discrepancy between immunohistochemical demonstration of p53 and molecular analysis, a large proportion of the former harbours the mutant form of the protein. In addition, p53 overexpression is positively correlated with PCNA LI, a finding which accompanies tumour progression.     

p53、p21~(WAF1)蛋白在非小细胞肺癌中的表达及其临床意义

目的　探讨原发性非小细胞肺癌中p5 3、p2 1WAF1蛋白表达与临床病理及预后的关系。方法　应用免疫组织化学 (SP法 )方法。共检测非小细胞肺癌 147例 ,其中腺癌 6 6例 ,鳞癌 6 3例 ,腺鳞癌 14例 ,大细胞癌 4例。结果　p5 3蛋白总阳性率为 6 1.2 % (90 / 147) ,腺癌为 5 7.6 % (38/ 6 6 ) ,鳞癌阳性率为 6 3.5 % (4 0 / 6 3) ,腺鳞癌为 71.4% (10 / 14) ,大细胞癌 2例阳性。p2 1WAF1蛋白总阳性率为40 1% (5 9/ 147) ,腺癌为 42 .4% (2 8/ 6 6 ) ,鳞癌为 41.3% (2 6 / 6 3) ,腺鳞癌 2 8.6 % (4 / 14) ,大细胞癌 1例阳性。肺腺癌p5 3蛋白阳性表达与其预后相关 ,6 6例腺癌中 ,生存率低于 3年组和高于 3年组的p5 3蛋白阳性率分别为 75 % (2 1/ 2 8)和 44 .7% (17/ 38) ,差异有显著性意义 (P <0 .0 2 5 )。p2 1WAF1阳性表达与肺癌预后有关 ,p2 1WAF1阳性表达者 3年生存率 (6 4.4% )高于阴性表达者 (4 6 .6 % ) (P <0 .0 5 )。p5 3阳性而p2 1WAF1阴性的非小细胞肺癌患者的预后比p5 3阴性而p2 1WAF1阳性者差 (P <0 .0 1)。结论　检测p5 3蛋白表达可作为判断肺腺癌预后的指标之一 ;检测p2 1WAF1蛋白表达有利于对非小细胞肺癌预后的判断 ;联合检测p5 3、p2 1WAF1蛋白对判断非小细胞肺癌的预后有重要的意义 ,似可作     

乳腺增生病p53基因第5外显子突变及其蛋白表达

目的：探讨p53基因在乳腺癌发生早期的作用。方法：用免疫组化方法检测36例乳腺单纯性增生、31例不典型增生、14例原位癌和16例浸润癌中p53蛋白的表达，用PCR－SSCP检测了上述组织中p53基因第5外显子突变。结果：p53蛋白在单纯性增生、不典型增生、导管内癌、浸润癌中的表达率分别为0、22.6%(7/31)、42.8%(6/14)、50％（8／16），PCR－SSCP在各组中均未检测到该基因第5外显子突变。结论：乳腺癌发生早期阶段有p53基因的参与，但与第5外显子突变无明显关系。     

Absence of p53 gene mutations in hepatocarcinomas from a Mediterranean area of Spain

 The incidence of p53 gene abnormalities in human hepatocellular carcinoma (HCC) varies in different geographical areas, being higher in regions where hepatitis virus infection and dietary exposure to aflatoxin B1 are the most common aetiological agents. These mutations are less frequently encountered in Europe, although some studies have reported p53 protein overexpression in up to 45% of cases analysed. We have analysed 129 tumour samples of primary malignant hepatic neoplasms recovered from paraffin blocks processed in two pathology laboratories in a Mediterranean area of Spain (Valencia and Gerona). Among 14 cases in which p53 immunohistochemistry expression proved positive, 5 stained in more than 50% of the cell nuclei. By PCR-SSCP analysis we could detect the complete sequence from exon 5 through 8 in 70 cases and part of this region in the remaining cases, but no mutations were found. We found no relationship with the clinical stage, tumour stage or clinical outcome. We conclude that p53 gene alterations are not a major event in the malignant transformation of hepatic cells in this region of the Mediterranean. The variable incidence of p53 gene alterations in other geographical areas may reflect a different genetic background for the aetiology of HCC. Received: 14 September 1998 / Accepted: 28 January 1999     

Malignant transformation of mature cystic teratoma to squamous cell carcinoma involves altered expression of p53‐ and p16/Rb‐dependent cell cycle regulator proteins

Ovarian mature cystic teratomas (MCT) uncommonly undergo malignant transformation to squamous cell carcinoma (SCC). While alterations in the p53 tumor suppressor gene and protein have been shown, few studies have analyzed other molecular changes leading to this malignant conversion. The purpose of the present study was to investigate 21 samples of SCC arising in MCT for altered expression in known p53‐ and p16/Rb‐dependent cell cycle regulatory proteins, and the association between their expression and cellular proliferation and histological features. Overexpression of the p53 protein was observed in 14 SCC (67%), while four (19%) had point mutations in the p53 gene. Reduced expression of the p16 protein was observed in 18 SCC (86%), while p16 gene alterations (hypermethylation (29%) and point mutation (33%)) were found in 11 (52%). Furthermore, a statistically significant correlation was observed between p53 and Rb overexpression (P = 0.0010), and the overexpression of both p53 and Rb was respectively significantly correlated with increased cellular proliferation. The results indicate that alterations in both the p53 and p16‐Rb pathways are associated with SCC arising in MCT.     

Frequency and spectrum of p53 mutations in gastric cancer — a molecular genetic and immunohistochemical study

The p53 tumour-suppressor gene plays an important role in gastric carcinogenesis. In an analysis of the spectrum of mutations of the p53 gene seen in 56 primary gastric carcinomas of various types and grades of differentiation, the entire coding sequence (exons 2–11) of the p53 gene was screened by single-strand conformation polymorphism analysis and direct genomic sequencing of polymerase chain reaction products. Intragenic restriction site polymorphisms and the probe YNZ22 were used for the detection of loss of heterozygosity (LOH) of the p53 gene locus on chromosome 17p. p53 overexpression was studied with the anti-p53 antibody CM-1. A total of 21 somatic alterations of the p53 gene were found. Twenty were base-pair substitutions, and one was an eight base-pair deletion. Six tumours with p53 mutations revealed LOH. Abnormalities in p53 expression were found in 17 tumour samples, of which 16 had gene mutations. The spectrum of mutations observed was consistent with the predicted spectrum for dietary mutagens associated with the metabolism of nitrogenous compounds, resulting in deamination of nucleic acids. Our findings suggest that p53 could be a primary target for mutations associated with dietary carcinogens in gastric carcinogenesis.     

Lowp53 protein expression in salivary gland tumours compared with lung carcinomas

Summary Fifty-one salivary gland tumours (23 pleomorphic adenomas, 5 Warthin's tumours, 12 mucoepidermoid carcinomas, 7 adenoid cystic carcinomas, 3 undifferentiated carcinomas and 1 acinic cell tumour) and 27 lung carcinomas (18 squamous cell carcinomas, 6 adenocarcinomas and 3 small cell carcinomas) were analysed immunohistochemically for the expression ofp53 nuclear phosphoprotein. Eight out of 51 (16%) salivary gland tumours werep53 positive. Three of these were benign and 5 malignant. All 3 benign salivary gland tumours were pleomorphic adenomas and expressed only occasional nuclear positivity with less than 1% of tumour cells positive. Of the 5p53-positive malignant tumours, 3 were mucoepidermoid carcinomas and 2 undifferentiated carcinomas. The malignant salivary gland tumours expressed more than 1% of positive nuclei in every case. Seventeen lung carcinomas werep53 positive (63%). Thirteen of these were squamous cell carcinomas, 3 were adenocarcinomas and 1 small cell lung carcinoma. The results show that mutations of thep53 gene may be infrequent in salivary gland tumours when compared with lung carcinomas. The relatively indolent course of some histological types of malignant salivary gland tumours could be associated with the preservation of the non-mutatedp53 gene in most of these tumours. The presence ofp53 positivity in some pleomorphic adenomas might, on one hand, suggest thatp53 gene alterations are also present in these tumours; on the other hand, the accumulation of thep53 protein in these tumours might also be due to some unknown mechanism, not necessarily related top53 gene mutation.