p53 protein expression in central nervous system neoplasms

Regulation of Chemosensitivity in Human Medulloblastoma Cells by p53 and the PI3 Kinase Signaling Pathway

In medulloblastoma, p53 expression has been associated with chemoresistance and radiation resistance and with poor long-term outcomes in the p53-mutated sonic hedgehog, MYC-p53, and p53-positive medulloblastoma subgroups. We previously established a direct role for p53 in supporting drug resistance in medulloblastoma cells with high basal protein expression levels (D556 and DAOY). We now show that p53 genetic suppression in medulloblastoma cells with low basal p53 protein expression levels (D283 and UW228) significantly reduced drug responsiveness, suggesting opposing roles for low p53 protein expression levels. Mechanistically, the enhanced cell death by p53 knockdown in high-p53 cells was associated with an induction of mTOR/PI3K signaling. Both mTOR inhibition and p110α/PIK3CA induction confirmed these findings, which abrogated or accentuated the enhanced chemosensitivity response in D556 cells respectively while converse was seen in D283 cells. Co-treatment with G-actin-sequestering peptide, thymosin β4 (Tβ4), induced p-AKT^S473 in both p53-high and p53-low cells, enhancing chemosensitivity in D556 cells while enhancing chemoresistance in D283 and UW228 cells. IMPLICATIONS: Collectively, we identified an unexpected role for the PI3K signaling in enhancing cell death in medulloblastoma cells with high basal p53 expression. These studies indicate that levels of p53 immunopositivity may serve as a diagnostic marker of chemotherapy resistance and for defining therapeutic targeting.

p53 in Low-grade Gliomas

Although the p53 tumor suppressor gene is well known to be involved in the pathogen esis of malignant astrocytomas, its significance in the development of low-grade glio mas, including the nonastrocytic tumors, remains underexplored. In an attempt to further understanding the molecular genetics of glial tumorigenesis, 37 low-grade gliomas of different histologic subtypes were screened for p53 mutations with the polymerase chain reaction, single-strand conformation polymorphism analysis and direct DNA sequencing. Forty-eight tumors, including the previously mentioned 37 cases, were examined immunohistochemically with paraffin-embedded tissues for p53 protein labeling. Only two diffuse astrocytomas exhibited p53 genetic abnormalities, and both tumors behaved aggressively. Two tumors exhibited p53 protein immuno labeling, including one of the cases with genetic changes. p53 genetic alterations are only rarely involved in the pathogenesis of low-grade gliomas. The authors speculate that they occur late in the transition from low-grade to high-grade tumors. Int J Surg Pathol 1 (3):163-170, 1994

A knowledge-based approach for predicting gene-disease associations

MOTIVATION

Recent advances of next-generation sequence technologies have made it possible to rapidly and inexpensively identify gene variations. Knowing the disease association of these gene variations is important for early intervention to treat deadly diseases and provide possible targets to cure these diseases. Genome-wide association studies (GWAS) have identified many individual genes associated with common diseases. To exploit the large amount of data obtained from GWAS studies and leverage our understanding of common as well as rare diseases, we have developed a knowledge-based approach to predict gene-disease associations. We first derive gene-gene mutual information by utilizing the cooccurrence of genes in known gene-disease association data. Subsequently, the mutual information is combined with known protein-protein interaction networks by a boosted tree regression method.

RESULTS

The method called Know-GENE is compared with the method of random walking on the heterogeneous network using the same input data. For a set of 960 diseases, using the same training data in testing in 3-fold cross-validation, the average recall rate within the top ranked 100 genes by Know-GENE is 65.0% compared with 37.9% by the state of the art random walking on heterogeneous network. This significant improvement is mostly due to the inclusion of knowledge-based mutual information.

AVAILABILITY AND IMPLEMENTATION

Predictions for genes associated with the 960 diseases are available at http://cssb2.biology.gatech.edu/knowgene

CONTACT

: skolnick@gatech.edu.

[Astrocytic neoplasms and correlation with mutate p53 and Ki-67 proteins]

The astrocytic neoplasms respond by 60% of the central nervous system tumors, being the study of the molecular biology an important step for the understanding of the genesis and biological behavior of these diseases. The Ki-67 proteins, which are markers of the cellular proliferation, and p53, which is the product of the tumor suppressor gene TP53, are both important tumoral markers. This study intends to identify and quantify the Ki-67 and p53 proteins in astrocytic tumors of different grades of malignancy, as well as to analyze their relations with age and gender. Ki-67 and p53 proteins in 47 patients with surgically resected astrocytic neoplasms were studied through immunohistochemistry. They have been previously classified and reviewed concerning their histological grade, as suggested by the World Health Organization. The immunomarked cellular nuclei were quantified by the program Imagelab-softium for the absolute parametric reason between the nuclei of the positive cells and the total amount of tumoral cells, being counted 1000 cells. The lineation used has been transversal not controlled. For the statistical analysis the variables were divided into groups. For the Ki-67 they were absent, <5% and >5% and for p53 they were absent (0), <25% (1+), between 25 and 50% (2+), between 50 and 75% (3+), and higher than 75% (4+). Ki-67 was present in 37 cases (78.72%) evidencing a correlation with a higher malignancy degree (p<0,001). p53 was present in 14 cases (35.13%) with a higher correlation with astrocytoma grade IV (p=0.59). There has not been a statistically significant correlation between p53 and Ki-67, as well as among these variables, age and gender. The hypotheses of a greater presence of Ki-67 and p53 in astrocytic neoplasms with a higher degree of malignancy, except for the correlation between grade III and p53, is corroborated by the results of this study.

Prognostic value of Mdm2, p53 and p16 in patients with astrocytomas

Surgical cure of gliomas infiltrating into the brain is practically impossible and their clinical course is primarily determined by the biological behavior of the tumor cell. The purpose of this study was to analyze retrospectively prognostic input of p53, Mouse double minute-2 (Mdm2) and p16 in 103 uniformly treated patients with astrocytic tumors. The expression of these molecules was measured by immunohistochemical procedure. Prognostic evaluation was performed with the multivariate proportional hazards model. The follow-up period lasted 19 (5-122) months for the survivors. We observed that 66% of gliomas showed mutated p53, while only 17% overexpressed Mdm2, the p53-regulatory molecule. Besides, almost 50% of gliomas lost p16 immunopositivity. Only p53 labeling showed a positive correlation with the grade of malignancy, according with the WHO classification. The association between mutated p53 and histological grade remained when prognostic variables were considered in a multivariate analysis. No association between p53 status and overall survival was found. On the other hand, Mdm2 overexpression and, unexpectedly, p16 immunopositivity were associated with a shorter survival in an univariate analysis. However, Cox-regression analysis showed that only Mdm2 in female patients was an independent prognostic factor, associated with shorter survival. In conclusion, our results suggest that Mdm2 could be a relevant marker in determining the evolution of glioma patients and could provide a more objective way to classify astrocytomas.

The impact of p53 tumor suppressor gene on glioma biology

The tumor suppressor gene, p53, is important in glioma biology. The authors of this paper review its role in cell physiology, epidemiology, glioma progression, prognosis, and therapeutic advances.

Cerebral metastases as first symptom of cancer: a clinico-pathologic study

Symptomatic brain metastases of carcinomas in patients without a previously diagnosed malignancy are frequent in neurosurgical series. Such tumors often lack distinctive morphological characteristics so that the routine histological examination can be unsuccessful in identifying the site of origin. Objectives of the present study were to evaluate the frequency of brain metastases as the only manifestation of an unknown primary cancer by the retrospective analysis of a series of consecutively operated single cerebral metastases; to verify the efficacy of clinical investigations in detecting the site of origin; to investigate whether the primary site can be identified by the immunohistochemical study of the neurosurgical specimens. Antibodies to the following antigens were used: carcinoembryonic antigen (CEA), carbohydrate antigen (CA) 19.9, CA 125, BCA-225, cytokeratin 20, PSA, HMB-45. Out of 181 patients operated for single cerebral metastasis of carcinoma, 99 (54.7%) were in patients without any previously diagnosed systemic neoplasm. In 26.7% the primary remained undiagnosed after clinical investigations, in 9 cases even at autopsy. PSA and HMB45 antibodies specifically identified metastases from prostate carcinomas and skin melanomas, respectively. No other specific immunophenotype was identified; the immunoreactivity of the single cases was more or less suggestive for a primary site. Precocious metastases of lung carcinomas expressed CEA more frequently than late metastases. It has been hypothesized that CEA plays some role as a contact mediating device. CEA expression can have some link with the tendency to metastasize precociously to the brain. No major difference of p53 and k-ras expression has been found in precocious versus late brain metastases.

Proliferation markers in different types of clinically non-secreting pituitary adenomas

160 clinically non-secreting pituitary adenomas were examined in regard to their expression of the markers PCNA, bcl2, Ki 67 in the mib-1 modification and p53 which are still under investigation for their relevance to cell proliferation. The series contained 60 null cell adenomas, 60 oncocytomas and 40 gonadotroph adenomas. The groups that showed a definitely negative and definitely positive staining were evaluated in regard to their further characteristics such as size, invasiveness and recurrence. PCNA showed a highly represented immunostaining index throughout the groups, but not correlation between the PCNA index and an increased recurrence rate could be found. The staining for bcl2 was only rarely positive and only in a small number of cells. No correlation with the clinical data could be seen. We found a significant higher rate of staining in the invasive adenomas in the group of null cell adenomas and oncocytomas for Ki 67, especially in those adenomas expressing p53. p53 positivity was restricted to the invasive adenomas but was found only in 20% of all invasive adenomas. These data confirm in a sufficiently large series of clinically endocrine inactive pituitary adenomas, that p53 and Ki67 immunohistology is useful in evaluating the aggressive behavior of clinically silent pituitary adenomas. Nevertheless, negative results do not exclude clinically relevant invasive behavior.

p53 protein expression in grade II astrocytomas: immunohistochemical study of 100 cases with long-term follow-up

p53 protein expression was evaluated by immunohistochemistry in a homogeneous series of 100 supratentorial grade II astrocytomas with long-term follow-up. The staining was positive in 72 cases. The proportion of p53 positive tumors was slightly higher in younger patients. The tumor regrowths which derived from p53 positive tumors were themselves p53 positive, and this p53 immunopositivity was often stronger than in the initial tumors. All of the 10 gemistocytic astrocytomas included in our series were p53 positive, and age more than histological type appeared decisive in prognosis. p53 protein expression did not quite reach statistical significance as an independent predictive variable in multivariate analysis, whereas survival was related with age, mass effect, surgery and tumor location. Only a tendency to a longer survival was observed on the curves in younger patients with mildly positive tumors.

Accumulation of p53 and Ki-67 expression do not predict survival in patients with fibrillary astrocytomas or the response of these tumors to radiotherapy

OBJECTIVE

Although radiotherapy is often used in the treatment of patients with low-grade astrocytomas, its value is still uncertain. Radiotherapy carries a risk of morbidity for patients and has time and cost implications for health services. We have assessed the value of two histological variables, p53 accumulation and Ki-67 expression, in predicting the response of astrocytomas to radiotherapy. The former antigen was assessed because many astrocytic tumors show mutations in the p53 gene, the function of which is crucial for mediating cell death after radiotherapy, and the latter was assessed because it is expressed only in proliferating tumor cells, which may show greater radiosensitivity than nonproliferating cells.

METHODS

Immunohistochemistry was used to detect the accumulation of p53 and expression of Ki-67 in a retrospective series of 96 patients with supratentorial fibrillary astrocytomas, 58 of whom had received postoperative radiotherapy. The immunohistochemical data were correlated with survival after radiotherapy.

RESULTS

There was no significant difference in survival between the patients who did and those who did not receive radiotherapy. The p53 and Ki-67 labeling indices did not correlate with survival in either the irradiated or the nonirradiated cohort, nor with overall survival in the series as a whole.

CONCLUSION

Immunohistochemical assessment of p53 accumulation and Ki-67 expression does not help in predicting the survival of patients with supratentorial fibrillary astrocytomas or in predicting whether particular patients are likely to benefit from radiotherapy.

Immunoreactivity of bcl-2, p53 and EGFr is associated with tumor stage, grade and cell proliferation in superficial bladder cancer. Finnbladder III Group

Immunoreactivity of bcl-2, p53, the epidermal growth factor (EGFr) and Ki-67 (MIB-1) proteins was assessed by immunohistochemistry in 185 patients with superficial bladder cancer (SBC) in order to evaluate their usefulness as indicators of tumor progression. Forty-one percent of the tumors were bcl-2 positive, 36% of them were positive for p53 (over 20% of nuclei), while 41% were positive for EGFr, and 30% of the tumors were MIB-1 positive (proliferation index > 15%). Immunoreactivity of all analyzed proteins was highly significantly related to tumor grade and stage. Tumors which were bcl-2, p53 or EGFr positive were also rapidly proliferative (MIB-1 score >15%). The obtained results suggest that all analyzed proteins may have prognostic significance in SBC. The prognostic value of the abnormal immunolabeling of the analyzed proteins will be established after an adequate follow-up period of this same cohort of patients.

Immunohistochemical Localization of p53 in Human Thyroid Neoplasms: Correlation with Biological Behavior

Molecular analyses of thyroid tumors have documented mutations in the tumor suppressor p53 gene almost exclusively in anaplastic carcinomas. In contrast, immunohistochemistry has localized p53 in differentiated papillary and follicular thyroid cancers. To establish the significance of p53 immunolocalization in these lesions, 78 thyroid tumors of follicular derivation were examined. All tumors were classified by strict criteria and the extent of tumor was determined morphologically. Immunohistochemical staining for p53 was performed on paraffin sections of formalin-fixed tumor tissue. The results of staining were correlated with diagnosis, tumor extent and clinical outcome. Immunopositivity for p53 was diffuse and strong in all five anaplastic carcinomas examined. There was no staining in five of six follicular adenomas. Four of nine follicular carcinomas had some degree of nuclear staining, but this was focal; all nine tumors were confined to the thyroid at the time of examination. Of 49 papillary carcinomas, 26 were intrathyroidal, and 7 of these were occult; there was no p53 positivity in any occult lesion and only S of the 19 palpable lesions stained. In contrast, among 23 papillary carcinomas with extra thyroidal extension or metastases, only 9 were negative for p53 immunoreactivity. Five of seven tall cell papillary carcinomas and one of two insular carcinomas had p53 immunopositivity and this correlated with aggressive behavior. These results support the tumorigenic role of p53 mutations postulated for anaplastic thyroid carcinomas and indicate that localization of p53 by immunohistochemistry is a useful prognostic index of clinical behavior in differentiated thyroid carcinomas of follicular cell derivation.

Analysis of proliferation markers and p53 expression in gliomas of astrocytic origin: relationships and prognostic value

Consecutive paraffin sections of 105 astrocytomas and 15 oligoastrocytomas were examined for expression of p53, MIB-1 (Ki-67), and proliferating cell nuclear antigen (PCNA). The tumors had been examined previously for genetic abnormalities and by flow cytometry. Regardless of the tumor's stage and grade and the patient's age and gender, p53 expression was found in 40% of tumors. Although p53 expression was associated with a loss on chromosome 17p and was more frequent in aneuploid tumors, it had no association with survival time. The MIB-1 and PCNA labeling indices increased with increasing tumor grade but showed no association with other clinicopathological parameters. In individual tumors, there was poor concordance between any of the variables (MIB-1, PCNA, and p53). Results for p53 and MIB-1 were similar for both astrocytomas and oligoastrocytomas. The MIB-1 and PCNA values appeared to have prognostic utility in univariate analysis but not after adjusting for patient age and tumor grade. The poor concordance between MIB-1 and PCNA in individual tumors indicates that any one means of assessing proliferative potential in gliomas may not be reliable.

MDM2 and p53 expression in gliomas: a multivariate survival analysis including proliferation markers and epidermal growth factor receptor

p53 and the murine double minute 2 (MDM2) oncoprotein expression was evaluated in paraffin-embedded tissue from 61 patients with central nervous system gliomas (53 astrocytomas and eight oligodendrogliomas) and related to proliferation-associated markers [i.e. proliferating cell nuclear antigen (PCNA), Ki-67 and nuclear organizer regions (NORs)] and epidermal growth factor receptor (EGFR). We used the monoclonal antibodies PC-10, MIB-1, DO-1, 1B1O and EGFR 113 and the colloid silver nitrate (AgNOR) technique. MDM2 and p53 were co-expressed in 28% of cases. A p53-positive/MDM2-negative phenotype was observed in 15% and a p53-negative/MDM2-positive phenotype in 20% of cases. There was a positive correlation of p53 and MDM2 expression with grade and proliferation indices. Univariate analysis in the group of diffuse astrocytomas showed that older age, high histological grade, high PCNA labelling index (LI) and high AgNOR score were associated with reduced overall survival (P < 0.05). p53 LI, Ki-67 LI, AgNOR score, tumour location and grade influenced disease-free survival (P < 0.05), whereas the only parameters affecting post-relapse survival were histological grade and Ki-67 LI (P < 0.1). Multivariate analysis revealed that age, radiotherapy, PCNA LI and p53 LI were the independent predictors of overall survival. p53 LI, Ki-67 LI, MDM2 LI, EGFR LI, grade and type of therapy were independent predictors of disease-free survival, and grade was the only independent predictor of post-relapse survival. Our results indicate that p53 LI and MDM2 LI, EGFR expression as well as proliferation markers (PCNA and Ki-67) are useful indicators of overall and disease-free survival in diffuse astrocytoma patients.

Immunohistochemical staining for the p53 protein and proliferating cell nuclear antigen in familial clustering of gastric cancer

Purpose of this study was to assess the role of p53 gene and tumor proliferating activity in familial clustering of gastric cancer.

MATERIALS AND METHODS

Among 344 patients who underwent resections for gastric cancer, 10 patients had two or more gastric cancer-affected, first-degree relatives. We classified them as the group of gastric cancer with family history (FGC). Eighty-seven patients with gastric cancer who had no relatives with any malignant neoplasm were classified as the sporadic group. The paraffin-embedded specimens were stained immuno-histochemically using monoclonal antibodies against the p53 product and proliferating cell nuclear antigen (PCNA).

RESULTS

There was no significant difference in any clinicopathologic factor and the PCNA labeling index between the two groups. Staining for the p53 product was positive in 80% of the FGC group and in 38% of the sporadic group (P < 0.05).

CONCLUSION

Our study suggests that overexpression of p53 protein is one of the familial factors that correlates with carcinogenesis in the stomach.

Cell growth and p53 expression in primary acquired melanosis and conjunctival melanoma

AIMS

To evaluate cell growth and the pattern of p53 suppressor gene expression in atypical primary acquired melanosis (PAM) and in recurrent conjunctival melanoma.

METHODS

Eighteen specimens of PAM with atypia and 24 specimens, comprising early and late lesions, from 12 patients with conjunctival melanoma were stained for the proliferating cell nuclear antigen using the PC10 antibody, and for the p53 gene product using the BP53-12-1, 1801 and DO7 clones. The immunoreactive cells were counted manually and the data evaluated statistically.

RESULTS

Seven of nine PAM specimens progressing to melanoma expressed PC10. None of these lesions expressed the p53 gene product. The number of proliferating cells was higher in the late than in the early lesions of conjunctival melanoma. Four of the 12 recurrent melanomas displayed focal, but minimal, p53 expression. The proliferating cell count in the p53 positive tumours was very similar to that of the p53 negative conjunctival melanomas.

CONCLUSION

Examination of the expression of proliferating cells in atypical PAM may be used as an adjunct to predict which lesions will progress to melanoma. The increase in the number of proliferating cells over time in recurrent conjunctival melanomas probably reflects more aggressive behaviour and may be used to monitor recurrence. The absence of p53 expression in PAM and minimal staining of conjunctival melanomas did not correlate with cell growth, suggesting that alterations in the p53 tumour suppressor gene are uncommon and late events in conjunctival melanoma, and that p53 expression is unlikely to be a useful prognostic indicator.

Comparative evaluation of p53-protein expression and the PCNA and Ki-67 proliferating cell indices in human astrocytomas

Mutations of the p53 gene are one of the most frequent genomic alterations of human tumours of astrocytic lineage. Because the physiological role of this gene is a suppression of cellular proliferation and growth, the overexpression of p53-protein may correlate with the expression of PCNA or Ki-67, established markers of cell proliferation. Paraffin-embedded surgical specimens from 60 human astrocytomas (9 pilocytic tumours, 12 WHO grade II, 9 anaplastic astrocytomas [WHO grade III] and 30 glioblastomas [WHO grade IV]) were stained with anti-PCNA (PC10), anti-p53(DO-7) and anti-Ki-67 antibodies (DAKO). Approximately 40% of all the cases were p53-protein immunopositive (53.3% glioblastomas, 33.3% anaplastic, 41.7% low grade astrocytomas but no pilocytic tumor). Statistical analysis did not reveal statistically significant correlation between p53-immunopositivity and PCNA or Ki-67 labeling indices. The Ki-67- and PCNA LI-s were statistically correlated, and the former better discriminated groups of different grades of malignancy.

Risk of nervous system cancer among workers exposed to lead

Experimental animal studies suggest that lead compounds may increase the risk of gliomas. To study whether occupational exposure to lead increases the risk, we followed nervous system cancer incidence among 20,741 employees biologically monitored for their blood lead (B-Pb) concentrations. We also performed a nested case-referent study, comprising 26 male cases of nervous system cancer (16 of which had gliomas). Those cases a B-Pb > or = 1.4 mumol/L had a twofold increase in the odds ratio of nervous system cancer as compared with those employees whose B-Pb had not exceeded 0.7 mumol/L. The excess was confined to gliomas (odds ratio 11, 95% confidence interval 1.0 to 630 for B-Pb > or = 1.4 mumol/L; overall P value for trend, 0.037). We obtained lifetime information on exposure and potential confounders for 58% of the cases. The odds ratio of glioma was associated with indices of lifetime exposure to lead, and potential confounders seemed not to explain the effects. The results suggest that there may be an association between occupational lead exposure and the risk of gliomas. No firm conclusions can be drawn because of the small number of cases and loss of material.

Outcome of 31 intracranial haemangiopericytomas: poor predictive value of cell proliferation indices

Cell proliferation indices of 31 primary intracranial haemangiopericytomas (HPC) and their recurrences and metastases were correlated with the long-term recurrence, metastasis and survival rates. Paraffin-embedded specimens were used for K-67, PCNA and p53 immunostainings and for estimation of S-phase fraction (S-PF) in flow cytometry. The median Ki-67 and PCNA indices and S-PFs were 10.4, 3.2, and 4.0 for primary HPCs and 14.1, 14.1, and 5.5 for recurrences, respectively. High indices were associated with higher recurrence, metastasis and death rates, but not at the p < or = 0.5 level. Consequently, these indices do not seem useful in planning of treatment and follow-up of meningeal HPCs. Meningeal HPCs, in contrast to meningiomas, recur almost always despite seemingly complete removal and often metastasize elsewhere in the body. This difference between two sharply demarcated tumours must reflect particularly adhesive and infiltrative properties of HPC cells and not just higher proliferation potential.

Epidermal growth factor receptor and p53 protein expression in human glioblastomas

p53 mutations and amplification of epidermal growth factor receptor (EGFR) gene are the most frequently detected genetic alterations in glioblastomas; thus, these changes seem to delineate two subgroups of glioblastomas: those originated de novo and those originated from preexistent low grade astrocytomas. Paraffin-embedded surgical specimens of 30 human glioblastomas were analyzed immunohistochemically for the presence of p53 protein and EGFR. Approximately half of the cases were p53 protein-positive while one-third were EGFR positive. Only three cases were positive for both p53 protein and EGFR. There was no difference between the average ages of patients with only-p53-positive, and double-negative tumors, while three glioblastomas with both p53 protein and EGFR immunopositivity occured in older patients (mean age 67.0 years, p < 0.02). Patients with only-EGFR-positive tumors were younger, but not significantly (44.3 years, p < 0.1). This study supports the notion that there are two main subpopulations of glioblastoma-with EGFR and with p53 protein overexpression.

p53 protein and epidermal growth factor receptor expression in human astrocytomas

p53 mutations are the most frequently detected genetic alterations of gliomas, appearing in a similar proportion of low and high grade astrocytomas, while the amplification of epidermal growth factor receptor (EGFR) gene appears mainly in glioblastomas. Thus, these changes seem to delineate two subgroups of high grade astrocytomas: those originating from preexistent low grade astrocytomas and those originating de novo. Paraffin-embedded surgical specimens from 56 human astrocytomas (8 pilocytic (I.) astrocytomas, 9 low grade (II.) fibrillary astrocytomas, 9 high grade (III.) anaplastic astrocytomas and 30 glioblastomas) were analyzed immunohistochemically for the presence of p53 protein and EGFR. Approximately 41% of all cases were p53-protein-positive while 23% were EGFR-positive. Five cases (8.9%) were double-positive for p53 protein and EGFR. The p53-immunopositive nuclei were revealed in 16 cases (53.3%) of glioblastomas, 3 cases (33.3%) of high grade and 4 cases (44.4%) of low grade astrocytomas. None of pilocytic tumors was p53-positive. EGFR immunopositivity increased with the grade of malignancy (11.1%, 22.2% and 33.3%). Double EGFR-p53-positive cases occuried in similar proportions in all grades (approximately 10%) and did not show different survival rate. There were no differences between average age of patients with only-p53-positive, p53-negative (pilocytic tumors excluded) and only-EGFR-positive tumors.

Prognostic indicators in a range of astrocytic tumours: an immunohistochemical study with Ki-67 and p53 antibodies

The treatment and prognosis of patients with cerebral astrocytic tumours are currently guided by histopathological classification. This study evaluates immunohistochemistry using Ki-67, an antibody to a nuclear protein expressed in proliferating cells, and DO-7, an antibody to the product of the tumour suppressor gene p53, as prognostic indicators for these tumours. Immunohistochemistry with Ki-67 has been correlated with the behaviour of many different tumours, but its value as a prognostic indicator in astrocytic tumours is diminished by the conflicting results of previous studies. Immunohistochemistry with antibodies to the p53 protein has been used as a prognostic indicator in melanomas and some carcinomas, but the relation between prognosis and accumulation of this protein in astrocytic tumours has not been clarified. We have tested the hypothesis that survival is correlated with Ki-67 immunolabelling indices (LIs) and patterns of p53 immunolabelling in the cerebral astrocytic tumours of a large cohort of patients (n = 123) for whom clinical indices were well documented. Astrocytic tumours were divided into three histological types: fibrillary astrocytoma (n = 24), anaplastic astrocytoma (n = 31), and glioblastoma (n = 68). Histological type and patient age were independent predictors of survival. Median Ki-67 LIs differed significantly (P < 0.0001) between the types of astrocytic tumour, and tumours with a Ki-67 LI < 2% had a significantly (P < 0.0001) better prognosis. Ki-67 LI as a continuous variable carried a significant (P = 0.0043) unadjusted hazard to survival which was lost when adjusted for other variables, notably histological type. By contrast, no relation was found between survival and three categories of p53 labeling (p53-negative, p53 LI < 40%, and p53 LI > 60%). The results indicate that, whereas Ki-67 immunohistochemistry predicts survival in patients with astrocytic tumours, conventional histological appraisal remains the best guide to prognosis, and immunohistochemistry for p53 has no value in the assessment of these tumours.

Mutations and immunohistochemistry of p53 and proliferation markers in astrocytic tumors of childhood

Thirty cases of hemispheric astrocytic tumors of childhood, consisting of 11 pilocytic astrocytomas, 2 fibrillary astrocytomas, 9 anaplastic astrocytomas, and 8 glioblastomas, were studied for the presence of p53 mutations and for immunohistochemical demonstrations of p53 and proliferation markers PCNA and Ki-67 MIB-1. The study was performed using polymerase chain reaction (PCR)-assisted single-strand conformation polymorphism analysis of exons 5-8 and direct sequence analysis of PCR products. For immunohistochemistry, DO1 and PAb 1801 were used. No mutation and no positivity for p53 protein were found in pilocytic astrocytomas. Mutations (at codons 144, 202, and 245) were found in 2 out of 8 glioblastomas and in 1 out of 9 anaplastic astrocytomas, whereas positive staining was found in 11 out of 17 malignant gliomas. Cases with mutations showed the highest p53 labeling index and also PCNA and MIB-1 labeling indices. The negative results in pilocytic astrocytomas are in line with the benign course of these tumors, whereas for malignant gliomas no difference seems to exist in comparison with adult cases.

Aberrant p53 expression does not correlate with the prognosis in anaplastic astrocytoma

Mutations of the p53 tumor-suppressor gene, as determined by the immunohistochemistry of archival formalin-fixed specimens, have been correlated with the prognosis for patients with many different types of malignancy. Similar correlations have been shown in series including patients with all grades of astrocytoma. We hypothesized that this might be a clinically useful prognostic indicator for patients with a defined grade of astrocytoma, anaplastic astrocytoma. This series comprised 54 consecutive patients with biopsy-proven anaplastic astrocytoma treated at one institution. When the CM-1 antiserum was used for testing, 33 (61%) of the 54 biopsies exhibited positive nuclear staining for p53, indicating an abnormal accumulation of the protein. This staining was graded according to the number of positive cells per high-power field. Positive immunohistochemical staining for p53 in the tumor cell nuclei did not correlate with the patient's outcome. Significant correlates of improved patient survival were the presentation with epilepsy in the absence of a neurological deficit (P = 0.005) and the surgeon's performance of a macroscopically complete surgical resection of the tumor (P = 0.01).

p53 but not erbB-2 expression is associated with rapid tumor proliferation in urinary bladder cancer

Tumor proliferation in bladder cancer is associated with tumor behavior. To assess the association between Ki-67 labeling index (LI), p53, and c-erbB-2 overexpression, formalin-fixed tissue samples of 160 patients with transitional cell carcinoma (TCC) of the urinary bladder were studied by immunohistochemistry. Ki-67 LI was strongly associated with tumor stage (P < .0001), tumor grade (P < .0001), and p53 status (P = .0014) but not with erbB-2 overexpression (P > .2). Ki-67 LI was higher in p53-positive tumors (19%) than in p53-negative tumors (14%) when all stages were compared. Ki-67 LI was independent of p53 expression in pTa tumors (p53-positive, 9%; p53-negative, 11%), showing that p53 overexpression alone is not sufficient to induce rapid tumor cell proliferation in pTa tumors. Ki-67 LI also was independent of p53 expression in pT2 to pT4 tumors (p53-positive, 20%; p53-negative, 23%), indicating that p53 expression is not necessary for rapid tumor cell proliferation in advanced stages. However, there was a striking difference in Ki-67 LI between p53-positive pT1 tumors (22.0% +/- 8.8 standard deviation [SD]; n = 20) and p53-negative pT1 tumors (9.7 +/- 8.3 SD; n = 22; P = .0001). These results suggest that increased proliferation in p53-positive pT1 tumors is caused by additional alterations that occur during tumor progression.

p53 immunohistochemical positivity as a prognostic marker in intracranial tumours

The frequency and scale of positive p53 immunohistochemistry in 107 intracranial tumours of different types was studied as a possible prognostic marker using a polyclonal antibody CM-1 which detects both the wild-type and mutated p53 proteins. Fifty of the tumours (46.7%) showed nuclear p53 positivity with different percentages of positive nuclei. The positivity was concentrated in glial tumours of which 52.8% were positive. Forty-two of seventy-four astrocytomas (56.8%), 4 of 12 oligodendrogliomas (33.3%), and 1 of 3 ependymomas (33.3%) showed p53-positive nuclei. Cytoplasmic positivity, found in 25 astrocytomas, was always associated with nuclear positivity. Some p53-positive nuclei were seen in 16.7% of the non-gliomatous tumours, but in all cases p53 positivity was seen in less than 1% of the nuclei. The patients with astrocytomas containing more than 5% p53-positive nuclei were younger (mean 27.3 years) (p = 0.016) and their tumours larger in diameter (mean 4.4 cm) (p = 0.05) than those with p53-negative astrocytomas (mean 41.0 years and mean 3.3 cm, respectively). In p53-positive (> or = 1% of nuclei) grade IV astrocytomas, survival time was significantly shorter (mean 7.2 months) than in p53-negative grade IV astrocytomas (mean 15.5 months (p = 0.024). The results indicate frequent p53 expression in intracranial tumours, especially in gliomas. The association of p53 positivity with young age, larger tumour size, and poor prognosis in high-grade astrocytomas suggests that p53 may be involved in the development of more aggressive types of intracranial tumours. According to these results, p53 immunohistochemical positivity may serve as a prognostic marker in high-grade astrocytomas.

Association of overexpression of p53 oncoprotein with the state of cell proliferation in oral carcinoma

p53 is a nuclear phosphoprotein recognised as important in the regulation of normal cell growth and proliferation, the wild-type protein suppressing cell division. Expression of presumptive mutant protein, detected by immunohistochemistry, is used increasingly as a diagnostic and prognostic marker in human neoplasms. A question arises as to whether or not p53 (over)expression in a lesion is any more or less informative than other markers of cell proliferation. Twenty well-differentiated oral squamous cell carcinomas which had earlier been examined for immunoreactivity against a panel of p53 antibodies were examined for the status of cell proliferation--both in islands of invading neoplastic cells and in the non-malignant epithelial margins. The status of epithelial cell proliferation was found to be significantly higher in p53-positive tumours when enumerated by Ki-67 antibody, both within the tumour as well as its margins. This may confer a growth advantage to these neoplasms and reflect a status of inactivated p53 protein, although the actual cause of the rapid proliferation may lie in activation/inactivation of other genes. The PCNA labelling indices, on the other hand, were closely similar in both p53-positive and -negative groups, suggesting that stabilisation of p53 protein does not influence the proliferative advantage in these carcinomas via a deregulation step of PCNA-related gene products.

Analysis of p53 gene mutations in low- and high-grade astrocytomas by polymerase chain reaction-assisted single-strand conformation polymorphism and immunohistochemistry

Using polymerase chain reaction-assisted single-strand conformation polymorphism (PCR-SSCP) and immunohistochemical analyses, mutations in the p53 tumor suppressor gene were examined in 19 low- and high-grade gliomas. By PCR-SSCP and nucleotide analyses, p53 gene mutation was seen in 7 gliomas. Out of the 7 mutations, 3 were located at the CpG site of the previously proposed hot-spot codons 248 and 273, 2 were at codons 171 and 214 and the other 2 were in intron 5, 1 at the splice acceptor site and the other in the vicinity of the splice donor site. The latter 4 mutations have not, or only rarely, been observed in gliomas or in other tumors. However, their effect on the structural and functional alteration of the p53 protein was suggested by positive intranuclear p53 immunostaining in neoplastic cells in 3 mutations including the 1 at the splice acceptor site. In connection with glioma grading, the p53 gene mutation was shown to have occurred in both low- and high-grade gliomas, often in most of the neoplastic cells, as suggested by lack of distinct normal bands and ladders in SSCP and direct sequencing, respectively. The absence of recurrence and malignant transformation over a considerably long postoperative time in our low-grade glioma cases suggested that the p53 gene mutation might not be sufficient for the progression from low- to high-grade gliomas. The frequency of detection of mutation was 7/19(37%) by PCR-SSCP, 8/19(42%) by immunohistochemistry and 10/19(53%) by both methods. The results of PCR-SSCP and immunohistochemistry were consistent in 14 cases (73.7%), but not in 5 cases(26.3%).(ABSTRACT TRUNCATED AT 250 WORDS)

p53 protein in low-grade astrocytomas: a study with long-term follow-up

The immunohistochemical expression of p53 protein (p53) was examined in 52 patients out of a series of 66 patients with low-grade astrocytomas with long-term follow-up. All patients were also evaluated for several clinical and histological features, among which only preoperative Karnofsky score and the extent of surgery were statistically significant parameters to predict outcome on multivariate analysis. p53 accumulation was seen in 46.1% of patients, with a wide range of percentage of positive cells. Median survival for p53-positive and p53-negative patients was 41 and 37 months respectively. The survival curves of p53-positive and -negative patients were not statistically different. However, the curves showed a trend towards a more aggressive course in p53-positive patients beginning 3-4 years after surgery. Five years after diagnosis the survival estimate with the Kaplan-Meier method was 21.2% for patients with p53-positive tumours and 45.9% for patients with p53-negative tumours. This trend is not due to different distribution of major clinical prognostic factors (age, incomplete resection or Karnofsky status). The trend could be related to the time needed by the p53-positive clone to outgrow the rest of the p53-negative neoplastic cell population. This hypothesis is further supported by the fact that the five recurrences which were surgically removed (one anaplastic astrocytoma and four glioblastomas) derived from p53-positive tumours and were themselves intensely p53 positive.

p53 immunoreactivity in oligodendrogliomas

Data are presented on p53 protein presence in human oligodendrogliomas whose progress from low grade to anaplastic oligodendroglioma can be followed. Expression was evaluated by formalin-fixed paraffin-embedded section immunohistochemistry, using monoclonal PAb 1801 antibody. The frequency of p53 protein accumulation is related to the stage of tumor malignancy. All the samples (100%) of malignant oligodendrogliomas were positive for p53 protein. Of 14 type II oligodendroglioma samples, 9 were positive (64%) while among type I oligodendroglioma the positivity was 28%. The mean proportion of reactive cells was also higher in malignant oligodendrogliomas. However, mean intensity staining did not differ among various grades of tumors. Our results point to the direct link between p53 protein accumulation and the malignant stage of human oligodendrogliomas. However, the value of p53 protein accumulation in predicting malignant behavior of oligodendrogliomas requires further confirmation.

p53, c-myc p62 and proliferating cell nuclear antigen (PCNA) expression in non-Hodgkin's lymphomas

AIMS

To investigate the immunohistochemical expression of p53 protein in non-Hodgkin's lymphomas (NHL) and its relation to that of c-myc p62 oncoprotein and proliferating cell nuclear antigen (PCNA).

METHODS

Paraffin wax embedded tissue from 90 non-Hodgkin's lymphomas (72 B cell and 18 T cell) was stained immunohistochemically for p53 protein, c-myc p62 oncoprotein, and PCNA using the monoclonal antibodies DO7, c-myc 1-9 E10, and PC-10, respectively.

RESULTS

Of the non-Hodgkin's lymphomas studied, 55 (61%) stained positively for p53 protein. The proportion of positive cases increased from low grade non-Hodgkin's lymphoma and was higher in tumours of T cell origin. The percentage of positive cells (labelling index or LI) was significantly lower in low grade non-Hodgkin's lymphoma, but no difference was established between intermediate and high grade non-Hodgkin's lymphoma. In a large proportion of low grade non-Hodgkin's lymphoma the LI was below 1%. c-myc p62 immunoreactivity was identified in all cases. A significant positive correlation was established between p53 LI and c-myc p62 LI (rs = 0.453) as well as between p53 LI and PCNA LI (rs = 0.338).

CONCLUSIONS

p53 immunoreactivity was present in about half the cases of non-Hodgkin's lymphoma and was related to the grade of malignancy and possibly to the B or T cell origin of the tumour. It was also associated with the proliferation state as expressed by PCNA LI and c-myc p62 expression, indicating that the expression of these three cell cycle-related genes might be interrelated.

Paraffin section p53 protein immunohistochemistry in neuroectodermal tumors

In an attempt to characterize the role of p53 alterations in the pathogenesis of intracranial neuroectodermal tumors, 196 tumors were immunostained with a monoclonal antibody against the p53 protein on archival materials of formalin-fixed, paraffin-embedded materials. Only 11% of well differentiated astrocytomas stained positive, whereas up to 40% of high-grade astrocytomas (anaplastic astrocytomas and glioblastoma multiforme) were immunolabelled. The extent of immunolabelling of tumor cells also increased from the low-grade to high-grade astrocytomas. Among the high-grade astrocytomas, the small anaplastic cells were the predominant cell type which exhibited aberrant p53 protein accumulation. Rare cases of oligodendrogliomas and medulloblastomas also stained positive, whereas ependymomas and choroid plexus tumors were uniformly negative. p53 alterations therefore appear to play a role in the progression from low-grade to high-grade astrocytomas and the cell type which appeared to be critically involved appeared to be the small anaplastic cells.

p53 expression in oat and non-oat small cell lung carcinomas: correlations with proliferating cell nuclear antigen

AIMS

To investigate the immunohistochemical expression of p53 protein in small cell lung carcinoma (SCLC), comparing it with that in non-small cell carcinoma (NSCLC); and to evaluate the correlation between p53 and proliferating cell nuclear antigen (PCNA) expression as well as between p53 and PCNA expression and survival.

METHODS

Paraffin wax embedded tissues from 61 cases of primary lung carcinoma were stained for p53 protein and PCNA using the monoclonal antibodies 1801 and PC-10, respectively, in a standard avidin-biotin immunoperoxidase method.

RESULTS

Of the 61 lung carcinomas 35 (57%) were positive for p53 (range 1% to 90%). Ninety percent of the non-oat SCLC contained positive cells and the labelling index (LI) was significantly higher than that of the oat SCLC (p < 0.001). SLCC also displayed a higher p53 LI than NSCLC (p < 0.01); no difference was found between squamous carcinoma, adenocarcinoma, and oat cell carcinoma. A p53 LI of greater than 1% tended to be associated with nodal metastases (p < 0.05), and p53 expression in node positive tumours as well as in oat cell carcinomas was indicative of poorer survival (p < 0.01 and p < 0.1, respectively). A p53 Li of greater than 60% was a negative prognostic factor in non-oat SCLC (p < 0.05). PCNA LI was highest in non-oat SCLC and lowest in NSCLC; oat cell carcinomas had a mean LI intermediate between NSCLC and non-oat SCLC (NSCLC v oat cell carcinoma p < 0.05 and oat cell v non-oat cell carcinomas p < 0.01). A PCNA LI was not correlated with nodal metastases or survival, but there was a significant positive correlation between PCNA LI and p53 LI (rs = 0.484, p < 0.001).

CONCLUSIONS

p53 and PCNA expression differ substantially among the various types of lung carcinomas. Substantial differences were also found between oat and non-oat types of SCLC, indicating that SCLC is heterogeneous as far as proliferation rate and altered p53 expression is concerned. p53 seems to be of some prognostic value. The relation between PCNA and p53 expression indicates that the PCNA gene is slightly upregulated by p53.

Expression of p53 in oligodendrogliomas

The expression of the nuclear protein p53 in oligodendrogliomas was investigated by immunohistochemistry, using a monoclonal anti-p53 antibody (DO-7) on formalin-fixed, paraffin-embedded material in 84 histologically verified cases, and compared with the histopathological grade and survival. p53-immunoreactive cells were found in 75 per cent of the samples acquired at the first biopsy. The p53 labelling index was not related to the degree of nuclear anaplasia. Tumour cases with more than 75 per cent p53 immunostained cells had a rapidly fatal clinical course. However, no significant correlation was found between p53 labelling index and tumour grade, mitotic index, or ploidy status. In most tumour recurrences (n = 25), the p53 labelling index increased or remained at the level of the first biopsy. In five cases (6 per cent), p53 was absent in the first sample as well as in the recurrence. Irrespective of the underlying aberration of either the gene or the metabolic pathway of p53, it is concluded that a high percentage (i.e., more than 75 per cent) of p53-immunolabelled cells is predictive of an unfavourable clinical course, while a percentage lower than 75 per cent immunoreactive cells does not exclude a rapid fatal outcome.

Patterns of immunohistochemical staining for proliferating cell nuclear antigen and p53 in benign and neoplastic human endometrium

Immunohistochemical staining was carried out on a spectrum of normal, hyperplastic and malignant endometrial curettings, for proliferating cell nuclear antigen--PCNA (using the monoclonal antibody PC10) and for abnormally stabilized p53 (using the polyclonal antibody CM-1). The mean proportion of glandular epithelial cells showing PCNA immunoreactivity was significantly lower in atypical hyperplasia/intra-endometrial adenocarcinoma than in invasive adenocarcinoma, but the degree of overlap between the cases was such that this was not considered to be of diagnostic value. p53 immunoreactivity was detected in 47% of invasive adenocarcinomas and in a much smaller proportion of endometria showing simple hyperplasia and atypical hyperplasia, but staining was only focal in the last two conditions. The majority of p53-positive invasive adenocarcinomas had a large proportion of glandular epithelial cells expressing PCNA, but a significant number of p53-negative cases also had a high PC10 index. This suggests that, in endometrial neoplasia, there is not a simple relationship between abnormally stabilized p53 and PCNA expression.

p53 protein overexpression identifies a group of central primitive neuroectodermal tumours with poor prognosis

Primitive neuroectodermal tumours (PNET's) or medulloblastomas are common primary brain tumours of childhood. Current treatment protocols achieve 50-60% cures. However, it has proved difficult to develop better treatment for the remaining patients because prognostic factors are not established. We have investigated the prognostic value of p53 protein expression in 87 PNET's using immunohistochemistry with DO-7 and CM-1 antibodies on biopsy paraffin sections. Eight patients (9%) had intensely reactive tumour cell nuclei, and a significantly reduced survival (P = 0.002); only one survives and this with a recurrent tumour 50 months following diagnosis. Sixty eight per cent of patients had faintly reactive tumour cell nuclei, a reduced survival up to 4 years but a long term survival not significantly different (P = 0.41) from 23% of patients with p53 negative PNET's; the 10 year survival rates were 37% and 40%, respectively. Males had a reduced survival (P = 0.04) with a 2-fold relative risk of death compared to females. Multivariate analysis showed that intense overexpression of p53 protein identifies a group of PNET patients with a 7-fold relative risk of death compared to all other cases, irrespective of sex. This marked difference suggests the involvement of p53 in the pathogenesis of PNET's which have a particularly poor response to treatment, and should help to develop new therapies for this group of patients.

Relationship of tobacco/alcohol use to p53 expression in patients with lingual squamous cell carcinomas

This study examined p53 expression immunocytochemically in 40 lingual squamous cell carcinomas from Dutch patients with known histories of smoking and/or drinking alcohol. 30% of neoplasms showed positive p53 reactivity, suggesting increased levels of p53 protein. No alcohol or tobacco risk factors were evident in 33.3% (4/12) of p53-positive neoplasms whereas only 7.1% (2/28) of p53-negative neoplasms showed an absence of these risk factors. 25% (3/12) of p53-positive neoplasms and 71.4% (20/28) of p53-negative neoplasms were found in patients who had been exposed to both alcohol and tobacco. A similar negative association with p53 reactivity was also found when either tobacco or alcohol were used in isolation. The results contrast with previous observations in head/neck and oral carcinomas and indicate that the association of alcohol/tobacco and p53 expression remains open to question.

Aberrant p53 expression in astrocytic neoplasms of the brain: association with proliferation

Aberrant expression of the p53 suppressor gene was evaluated in 102 cases of astrocytic neoplasms. Immunohistochemical staining with a monoclonal antibody (DO-7) and a polyclonal antibody (CM-1) to p53 protein (both wild type and mutant) on formalin-fixed paraffin sections showed a strong correlation with malignancy grade. The staining was positive in 49% of malignant neoplasms (grades III and IV) and in 19 to 29% of grade II astrocytomas, whereas none of the grade I tumors were positive. p53 expression was significantly associated with proliferation rate determined by immunohistochemical proliferating cell nuclear antigen (PCNA)-staining (median PCNA-labeling index (%): 4.22 (DO-7-positive) versus 1.18 (DO-7-negative), P < 0.0001; 4.02 (CM-1-positive) versus 1.18 (CM-1-negative), P < 0.001). Interestingly, in the glioblastoma group (n = 44), p53-positive tumors had higher proliferation indices, suggesting that histologically similar tumors could be divided into prognostically different subgroups by immunohistochemical demonstration of aberrant p53 expression.

p53 protein expression in central nervous system tumors: an immunohistochemical study with CM1 polyvalent and DO-7 monoclonal antibodies

Formalin-fixed, paraffin-embedded surgical specimens from 137 primary central nervous system tumors, including 26 astrocytomas (21 fibrillary, 1 protoplasmic, 1 gemistocytic and 3 pilocytic), 26 anaplastic astrocytomas, 9 glioblastomas, 1 gliosarcoma, 8 oligodendrogliomas, 4 ependymomas, 1 anaplastic ependymoma, 2 subependymomas, 3 paragangliomas, and 57 meningiomas, were immunostained with the CM1 polyclonal (pAb) and the DO-7 monoclonal (mAb) antibodies against the p53 protein, using the streptavidin/peroxidase method. In addition, two series of 17 and 9 medulloblastomas were also immunostained with the above pAb and mAb, respectively. p53 protein expression was observed in 7 fibrillary astrocytomas, 17 anaplastic astrocytomas, 5 glioblastomas, 1 gliosarcoma, 1 oligodendroglioma, 1 anaplastic ependymoma, and 4 meningiomas with the CM1 pAb. An additional 10 cases (i.e., 3 anaplastic astrocytomas and 7 meningiomas) were found to be p53 protein positive with the DO-7 mAb. Of the medulloblastomas, 8 (of the 17) and 4 (of the 9) were found to express p53 protein with CM1 pAb and DO-7 mAb, respectively. Our results indicate that p53 protein is expressed in a number of central nervous system neoplasms, and suggest that in astrocytic tumors a possible association may exist between p53 protein expression and tumor progression through increasing histological grades of malignancy.

p53 protein expression in non-neoplastic lesions and benign and malignant neoplasms of soft tissue

Alterations of the p53 tumour suppressor gene, with consequent nuclear p53 protein accumulation, are among the most common genetic lesions in human neoplasms. In the present paper we show p53 immunoreactivity in 65% of malignant and 21% of intermediate malignancy soft tissue tumours, and in 48% of benign/reactive soft tissue lesions. p53 immunoreactivity of sarcomas can be interpreted as an indirect indication of a mutation of the corresponding p53 gene, suggesting that its alteration may have a role in their pathogenesis. Our data on p53 immunoreactivity in benign lesions of the soft tissues are among the first demonstrations of p53 over-expression in benign/reactive conditions. We cannot exclude mutations of the p53 gene in these cases, but it is difficult to sustain this hypothesis in reactive/pseudoneoplastic lesions. Alternatively p53 immunoreactivity in benign processes could be due to an increase in wild-type p53 as a result of different physiological mechanisms (cell type-specific p53 regulation, cell maturation, DNA repair). Our results do not indicate that immunohistochemical demonstration of p53 expression is a marker of malignancy in soft tissue tumours and therefore is of limited use in differential diagnosis. However, they suggest the need for further molecular genetic studies in order to elucidate the biological significance of the abnormal expression of p53 in benign soft tissue lesions.