The p53 tumor suppressor gene frequently is altered in gynecologic cancers

Quantification of p53 in epithelial ovarian cancer

OBJECTIVE

The perceived function of wild-type p53 is suppression of cell proliferation. An alteration in the p53 tumor suppressor gene is a common defect in human malignancies. The purpose of this study was to prospectively determine whether p53 expression, as quantified by image analysis, was related to traditional prognostic indicators as well as survival in patients epithelial ovarian cancer.

METHODS

Eighty-three consecutive patients with epithelial ovarian cancer had their p53 expression studied by immunohistochemical staining and quantified by image analysis. Unless otherwise noted, p53 expression was reported as the percentage positive nuclear area staining.

RESULTS

The mean follow-up was 37 months (median, 30 months; range 24-55 months). In patients with serous carcinomas of the ovary, the mean p53 expression was 29.4%, whereas in patients with other histologies, the mean was 10.5% (P < 0.001). The tumors of patients with stage III or IV tumors stained significantly higher (mean 28. 7%) than the tumors of patients with stage I or II disease (mean 8. 36%) (P < 0.001). The tumors of patients with disease which could be optimally cytoreduced stained significantly lower (mean 23.0%) than the tumors of patients whose disease was unable to be optimally cytoreduced (mean 28.6%) (P = 0.041). Utilizing survival as the endpoint for multivariate analysis, FIGO stage (P = 0.006), p53 expression (P = 0.046), and the level of cytoreduction (P < 0.001) were independent prognostic indicators.

CONCLUSION

Image analysis allows quantitative measurements of p53 staining. p53 staining is significantly higher in advanced-stage, high-grade tumors which are unable to be cytoreduced than in early-stage, low-grade tumors which can be optimally cytoreduced. p53 expression is an independent prognostic indicator of survival in patients with epithelial ovarian carcinomas.

Establishment and characterization of human ovarian carcinoma cell lines

Five human ovarian carcinoma cell lines cultured from primary and metastatic tumors of Korean patients were characterized. These lines were isolated from two papillary serous cystadenocarcinomas, two endometrioid carcinomas, and one malignant Brenner tumor. It was shown that the growth of these cell lines was stable when cultured after at least 20 passages. Population doubling times varied from 40 to 67 hr. All lines showed high viability and were proven by DNA fingerprinting analysis to be unique. Contamination by mycoplasma or bacteria was excluded. In two lines, SNU-8 and SNU-840, an elevated level of CA125 antigen secretion could be detected, whereas CEA was undetectable in all five lines. Four different mutations in functional and highly conserved regions of the p53 gene were identified in three of our five lines (60%), namely in SNU-119, SNU-251, and SNU-563. Included were two missense mutations, one in-frame 3-base-pair deletion, and one out-of-frame 1-base-pair deletion. It is interesting to note that one of these three lines, SNU-251, presented an additional simultaneous nonsense mutation of the BRCA1 gene and missense mutation of the hMLH1 gene. In its lacking both wild-type alleles of the BRCA1 gene, SNU-251 might serve as an unusual and important in vitro model for studies related to ovarian carcinoma and the BRCA1 gene. It is thus likely that the establishment and characterization of these permanent human ovarian carcinoma cell lines in continuous cultures can provide useful tools for in vitro studies related to human ovarian carcinomas.

Molecular profile of advanced-stage transitional cell carcinoma of the ovary

OBJECTIVES

Our purpose was to determine the molecular profile of advanced-stage transitional cell carcinoma in terms of immunostaining for p53, epidermal growth factor receptor and HER-2/neu, deoxyribonucleic acid index, and S-phase fraction and to analyze the prognostic significance of these markers.

STUDY DESIGN

Archival paraffin-embedded tissue blocks from 29 advanced stage transitional cell carcinomas were obtained. Selected sections of the primary tumors were immunostained for p53, epidermal growth factor receptor, and HER-2/neu; deoxyribonucleic acid ploidy and S-phase fraction were determined with use of flow cytometry. Clinical information was abstracted from the medical records. Survival times were analyzed according to the life-table methods of Kaplan and Meier, and the statistical significance of the various factors was tested with the log-rank test. The proportional hazards model of Cox was used to identify prognostic factors.

RESULTS

Positive immunostaining was observed for p53 in 13 cases (45%), for epidermal growth factor receptor in 14 cases (50%), and for HER-2/neu in 19 cases (65%). Tumors were diploid in 16 cases (55%) and aneuploid in 13 (45%). The S-phase fraction was < or = 15% (mean) in 13 cases (45%) and > 15% in 16 cases (55%). The median survival for the entire group was 52 months. None of the above variables had a significant effect on survival time.

CONCLUSION

Neither immunostaining for p53, epidermal growth factor receptor, and HER-2/neu nor deoxyribonucleic acid ploidy nor S-phase fraction allowed us to distinguish transitional cell carcinoma from other more common epithelial ovarian cancers. In addition, no prognostic significance was associated with these biomarkers. A study of larger numbers of cases may be more elucidative.

Racial disparity in overexpression of the p53 tumor suppressor gene in stage I endometrial cancer

OBJECTIVE

This study was conducted to determine whether overexpression of the p53 tumor suppressor gene is associated with poor outcome in early-stage endometrial cancers and whether a racial difference in the frequency of p53 overexpression contributes to the observed racial disparity in survival rates.

STUDY DESIGN

Immunostaining for the p53 gene was performed in 164 women with stage I endometrial adenocarcinomas.

RESULTS

Overexpression of mutant p53 protein was seen in 28 out of 164 (17%) cases and was associated with a poor histologic grade (p = 0.003) and a nonendometrioid histologic appearance (p = 0.06). Overexpression also was three times more frequent in blacks (15 out of 44, 34%) than in whites (13 out of 117, 11%) (p = 0.003). Recurrent disease developed in 15 out of 164 (9%) cases and was more than twice as frequent in cases when the p53 gene was overexpressed (5 out of 28, 18%) than in cases with normal expression (10 out of 136, 7%). Recurrent disease was seen in 6 out of 44 (14%) blacks compared to 9 out of 117 (8%) whites.

CONCLUSIONS

These data support the hypothesis that differences in the frequency of alteration of the p53 tumor suppressor gene contribute to the racial disparity in endometrial cancer survival.

TP53 protein accumulation and gene mutation in relation to overexpression of MDM2 protein in ovarian borderline tumours and stage I carcinomas

Three hundred and seventy-four early-stage ovarian tumours, including 27 borderline tumours and 347 stage I carcinomas, were investigated immunohistochemically for overexpression of the TP53 and MDM2 proteins. TP53 (p53) and MDM2 alterations were detected in 15 and 4 per cent of borderline tumours, and in 50 and 13 per cent of stage I carcinomas, respectively. Mutations in the TP53 gene (exons 5-8) were demonstrated in 29 of the 50 stage I carcinomas studied, using denaturing gel electrophoresis followed by direct sequencing. TP53 overexpression was seen less often in tumours of mucinous and endometrioid type than in tumours of other histological types and more often in moderately and poorly differentiated than in well differentiated tumours. MDM2 protein overexpression was seen more often in clear cell carcinoma than in tumours of other histological types. These results indicate that TP53 abnormalities play a crucial role, and MDM2 abnormalities a minor role, in the development of early-stage ovarian carcinoma. There was no significant association between TP53 or MDM2 alterations and survival in multivariate analysis.

Gene therapy for ovarian cancer: development of novel treatment strategies

In the last decade, advances in molecular biology have lead to the development of techniques that permit the manipulation of mammalian cell DNA for diagnostic and therapeutic purposes. Gene therapy has subsequently evolved as a treatment option in patients with malignancies. In this article, we have summarized current strategies in gene therapy for ovarian cancer.

p53 overexpression in advanced-stage endometrial adenocarcinoma

OBJECTIVES

Mutation and overexpression of the p53 tumor suppressor gene in endometrial cancers are associated with advanced stage and poor survival. We sought to determine whether p53 overexpression is an independent variable predictive of poor prognosis in advanced endometrial adenocarcinomas.

STUDY DESIGN

Immunohistochemical evaluation was used to examine p53 expression in paraffin blocks from 179 endometrial adenocarcinomas.

RESULTS

p53 overexpression was seen in 35% of cancers and was associated with higher stage (p = 0.004), black race (p < 0.001), higher grade (p = 0.02), lack of hormone replacement (p = 0.04), and older age (p = 0.05). In addition to a higher frequency of p53 overexpression (57% vs 26%), black women had a lower survival rate than white women (p = 0.001), but overexpression was associated with poor survival in both races. After we corrected for hormone use, multivariate analysis revealed that older age (p < 0.001), higher stage (p < 0.001), higher grade (p = 0.01), and p53 overexpression (p = 0.04) were predictive of poor survival.

CONCLUSIONS

Overexpression of p53 in advanced-stage endometrial cancers is an independent variable that is associated with poor survival, occurs more frequently in black women, and may contribute to the racial disparity in survival.

Immunostaining of p53 protein in ovarian carcinoma: correlation with histopathological data and clinical outcome

OBJECTIVE

The objective of this study was to analyze the incidence of immunohistochemically detectable p53 protein accumulation in epithelial ovarian carcinomas and to correlate these data with the clinical outcome so as to clarify further the role of p53 mutations in prognosis with these patients.

METHODS

Tumor tissues from 179 patients with epithelial ovarian carcinoma were used for immuno-histochemical analysis with monoclonal antibody DO1 and BP 53-12-1 on formalin-fixed, paraffin-embedded tissue.

RESULTS

A total of 78 cases (44%) showed positive nuclear p53 staining. The p53-positive cases were found in all histological types of epithelial ovarian tumors. p53 staining was found in tumors of all stages with a higher percentage of positive cases in stage IV ovarian carcinomas (not significant). Poorly differentiated carcinomas showed a significantly higher percentage of p53 protein expression than did highly differentiated tumors (P = 0.0002). Clinical follow-up of up to 14 years (median 25 months) showed a slightly but not significantly shortened disease-free and overall survival time for patients with p53-positive epithelial ovarian carcinomas.

CONCLUSIONS

We conclude from our data that p53 expression in ovarian carcinoma is associated with poor differentiation but not with the disease being in an advanced stage. There was a tendency for shortened disease-free and overall survival for patients with p53-positive tumors.

Expression of cell regulatory proteins in ovarian borderline tumors

BACKGROUND

Tumors of borderline malignancy are still a controversial subgroup of ovarian neoplasms. The expression of several cell regulatory proteins was studied to characterize the molecular phenotype of these tumors, and to compare them with their benign and malignant counterparts.

METHODS

Specimens from 22 patients with tumors of borderline malignancy (11 serous and 11 mucinous tumors), 12 patients with benign tumors, and 16 patients with invasive ovarian carcinomas were evaluated for expression of epidermal growth factor receptor (EGFR), HER-2/neu, PTP1B, and p53 by immunohistochemical techniques.

RESULTS

One or both of the tyrosine kinase growth factor receptors EGFR and HER-2/neu was expressed by 42% of benign, 59% of borderline, and 81% of malignant ovarian tumors. EGFR was expressed in a significantly greater fraction of malignant lesions (69%) than borderline lesions (18%) (P< 0.004). EGFR expression was not observed among the 11 mucinous borderline tumors. HER-2/neu was expressed by 50% of borderline tumors and was not a marker for malignancy. The tyrosine phosphatase PTP1B was expressed by a similar fraction of benign (17%), borderline (27%), and malignant (19%) tumors. The number of cases studied precluded correlation of kinase and phosphatase activity. However, among 12 tumors with PTP1B expression, 9 also expressed EGFR or HER-2/neu. Overexpression of p53 was observed only in malignant serous tumors and was not found in malignant mucinous, borderline, or benign lesions.

CONCLUSIONS

Either EGFR or HER-2/neu was detected in a majority of borderline cancers. PTP1B was present only in a minority of these cancers. Frankly malignant serous lesions differed from borderline and benign tumors with regard to expression of EGFR and overexpression of p53.

Lack of mutation in tumour-suppressor gene p53 in gestational trophoblastic tumours

The objectives of this study were to better our understanding of the carcinogenesis of gestational trophoblastic tumours and to investigate the possible presence of mutational alteration of the p53 tumour-suppressor gene in these tumours. Amplification-based direct DNA sequencing was performed on 14 hydatidiform moles, six invasive moles, eight choriocarcinomas and ten normal early placental tissues. No mutation in exons 5-8 was detected in any of these 38 tissue specimens. These results suggest that a mutation in p53 tumour suppressor either does not exist or is a very rare event in gestational trophoblastic tumours. The gestational trophoblastic tumours probably involve a tumour-suppressor gene other than p53 gene or may follow a completely different pathway to their malignant phenotype.

Diethylstilbestrol-induced immortalization of human endometrial cells: alterations in p53 and estrogen receptor

Carcinogenesis is a process requiring multiple steps. Immortalization is one step in this process and may be rate limiting. To further our understanding of estrogen-induced carcinogenesis, we evaluated diethylstilbestrol (DES)-induced immortalization of human endometrial stromal cells. This was achieved by assessing at the restrictive temperature the colony-forming efficiency of cells that were conditionally immortalized with a temperature-sensitive simian virus 40 large T antigen. Treatment with DES for 1 wk did not increase the immortalization frequency; however, cultures that were treated for 20 wk had a twofold increase in immortalization frequency, and continued treatment for a total of 44 wk produced a threefold increase in immortalization frequency that was dose dependent. DES-treated restrictive temperature variants (RTVs) but not spontaneous RTVs lost the temperature-sensitive phenotype. DES-RTVs also had a shorter doubling time than spontaneous RTVs did. p53 expression was increased in DES-RTVs, and its localization within the cell was altered. Conversely, expression of the estrogen receptor was decreased in DES-immortalized cells. These changes in gene expression often occur in estrogen-related malignancies, and our results are consistent with a causal role for estrogens in these p53 and the estrogen receptor alterations. Immortalization of human cells may be analogous to initiation of rodent cells, and our results suggest that estrogen-induced alterations in p53 or other genes that regulate life span could contribute to estrogen-induced initiation.

Molecular basis of endometrial cancer

BACKGROUND

Most human cancers are thought to arise from alterations in oncogenes and tumor suppressor genes.

METHODS

Molecular techniques have been used to identify specific genetic alterations in endometrial cancers.

RESULTS

Overexpression of the HER-2/neu oncogene occurs in 10% of endometrial cancers and correlates with poor survival. Alterations in other receptor tyrosine kinases (c-fms and epidermal growth factor receptor) also occur in some cases. The c-myc oncogene, which encodes a nuclear transcription factor, also may be overexpressed in some invasive cancers. Mutations in the K-ras oncogene occur in 10% and in 20-30% of American and Japanese endometrial cancers, respectively. K-ras mutations also have been observed in endometrial hyperplasias, and this may represent an early event in the development of some cancers. Mutation of the p53 tumor suppressor gene, with resultant overexpression of mutant p53 protein, occurs in 20% of endometrial adenocarcinomas. Overexpression of p53 is associated with advanced stage and poor survival. Because p53 mutations do not occur frequently in endometrial hyperplasias, this may be a relatively late event in endometrial carcinogenesis. Recent studies have shown that mutations occur in microsatellite sequences in some endometrial cancers. Because microsatellite instability in hereditary nonpolyposis colon cancer has been found to be caused by mutations in DNA repair genes, similar mutations are being sought in endometrial cancers.

CONCLUSIONS

Although several molecular alterations have been identified, the molecular pathogenesis of endometrial cancer remains poorly understood.

Mutation of tumor suppressor gene p53 is frequently found in vulvar carcinoma cells

OBJECTIVE

The purpose of this study was to evaluate the presence and type of mutations of the tumor suppressor gene p53 in squamous carcinoma cell lines of the vulva.

STUDY DESIGN

Eight low-passage cell lines established from vulvar carcinoma were included in the analysis. Mutational analysis was restricted to exons 5 through 9 of the p53 gene, previously shown to have a high incidence of mutations. The sequences containing exons 5/6,7, and 8/9 were amplified by polymerase chain reaction and screened with a single-strand conformation polymorphism technique on PhastSystem (Pharmacia Biotech, Uppsala, Sweden). Exons from samples showing mobility shifts in single-strand conformation polymorphism were sequenced by polymerase chain reaction direct sequencing.

RESULTS

Five vulvar carcinoma cell lines showed abnormal electrophoretic mobility of exons 5/6, one of exons 8/9, and one of exon 7. Reduction to homozygosity was detected in four vulvar carcinoma cell lines. Missense mutations were detected by sequence analysis in UM-SCV-2 (codon 171: GAG[Glu]-->TAG[STOP]), UM-SCV-3 (hot spot codon 273: CGT[Arg]-->TGT[Cys]), UM-SCV-4 (codon 151: CCC[Pro]-->CAC[His]), UM-SCV-5 (codon 155: ACC[Thr]-->ATC[lle]), and UM-SCV-7 (codon 245: GGC[Gly]-->AGC[Ser]). UM-SCV-3 also carried a missense mutation with no amino acid change (codon 314: TCC[Ser]-->TCT[Ser]). UM-SCV-7 carried an additional base deletion at codon 249 (AGG-->AG-), likely resulting in a frameshift in transcription and a truncated protein product. Four of the seven mutations were transitions, two were transversions, and one was a deletion. The presence of transitions suggests that at least a proportion of p53 mutations of these cancers may arise spontaneously without exogenous carcinogen exposure. UM-SCV-1A and UM-SCV-1B were derived from the primary tumor and pleural effusion of the same patient. UM-SCV-6 is a cell line that contains human papillomavirus 16. No mutations in these three cell lines were found by single-strand conformation polymorphism.

CONCLUSIONS

On the basis of previous observations, loss of tumor suppressor p53 function either by mutation or human papillomavirus involvement is a frequent phenomenon in cervical carcinoma cells. It appears now that functional inactivation of p53 is associated also with vulvar carcinoma cell lines, but mutations of the p53 gene are much more common in vulvar than in cervical carcinoma cell lines.

Expression of cell cycle regulatory proteins (p53, pRb) in the human female genital tract

PURPOSE

Recent studies have shown that proliferation and differentiation of various cell types is regulated by cell-cycle-related proteins, such as protein p53 and retinoblastoma protein pRb.

METHODS

Three monoclonal antibodies to p53 (PAb240, PAb421, and PAb1801) and 3H9 monoclonal antibody to pRb were utilized for localization of proteins by peroxidase immunohistochemistry in frozen tissue sections.

RESULTS

Nuclear and nucleolar p53 expression was detected in nondividing and relatively stable cells, e.g., oocytes in primordial follicles and granulosa lutein cells. On the other hand, strong cytoplasmic p53 expression was detected in proliferating and low differentiated epithelial cells of the ovarian surface epithelium, amnion, endocervix and ectocervix, indicating enhanced p53 synthesis. Not all three p53 antibodies reacted with each tissue, perhaps due to structural and conformational changes in the p53 molecule, accompanying p53 association with other proteins, e.g., tissue specific transcription factor interactions. pRb expression was usually restricted to the cell nuclei and nucleoli. However, glandular cells of the female reproductive tract showed cytoplasmic pRb expression in juxtaluminal (secretory) segments of cells, a feature not previously described in any cell type. p53 and pRb immunoreactivities declined with advanced differentiation of cells. No p53 or pRb was detected in placental syncytiotrophoblast or terminally differentiated squamous epithelial cells.

CONCLUSION

Our data indicate that large quantities of p53 are synthesized in cells leaving the cell cycle and entering differentiation. Except in glandular cells, the pRb expression is confined to the cell nuclei and nucleoli. A unique cytoplasmic expression of pRb in juxtaluminal segments of glandular cells suggests a role for pRb in human female fertility and conception.

Biomarkers in the endometrium

A number of oncogenes and tumor suppressor genes that may serves as surrogate biomarkers of transformation are altered during the process of endometrial carcinogenesis. Overexpression of HER-2/neu occurs in 10% of endometrial adenocarcinomas and correlates with intraperitoneal spread of disease and poor survival. The c-myc oncogene is amplified in 10% of cases. Point mutations in codon 12 of the K-ras oncogene have been reported to occur in 10-20% of endometrial cancers. K-ras mutations also have been noted in some endometrial hyperplasias, which may represent an early event in the development of some endometrial cancers. Mutation of the p53 tumor suppressor gene, with resultant overexpression of mutant p53 protein, occurs in 20% of endometrial adenocarcinomas. Overexpression of p53 is associated with advanced stage and poor survival. Because p53 mutations have not been observed in endometrial hyperplasias, this is thought to be a relatively late event in endometrial carcinogenesis. Microsatellite instability has also been noted in approximately 15% of sporadic endometrial cancers, but mutations in DNA repair genes have not yet been reported. Chemoprevention trials in endometrial cancer may be feasible due to the existence of a premalignant lesion and surrogate biomarkers.

Identification of p53 mutations in endometrial adenocarcinoma by polymerase chain reaction-single-strand conformation polymorphism

OBJECTIVE

We determined whether mutations in p53 exons 5-6-7-8, as detected in the polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) test, might be correlated with stage or grade in endometrial adenocarcinoma.

METHODS

We amplified sequences containing exons 5, 6, 7, or 8 in DNA from tumors and controls. Mutation within the amplified sequences was indicated by changes in electrophoretic mobility (band shifts) in the SSCP test. The results were analyzed statistically and compared with the results of other, similar studies.

RESULTS

We identified 15 band shifts among 47 endometrial tumors studied (band shifts in two different exons in two cases) and none among 42 controls. Band shifts in exons 5 and 8 were associated uniformly with grade 2 or grade 3 histology. In other studies p53 mutations were correlated with advanced-stage malignancy.

CONCLUSION

Further evaluation of particular p53 mutations and their relation to disease course in endometrial adenocarcinoma seems warranted. The PCR-SSCP test seems well-suited to this purpose.