Comparison of p53 immunoexpression with allelic loss of p53 in ulcerative colitis-associated dysplasia and carcinoma

We correlated p53 overexpression with allelic deletion of p53 in ulcerative colitis (UC) with high grade dysplasia (HGD, n=12) and carcinoma (CA, n=8). Sections were immunostained against p53 and epithelium was microdissected on consecutive sections with subsequent amplification for LOH of p53 (17p). Staining with anti-p53 was positive in HGD (9 of 12) and CA (7 of 8). Percent positive cells were less in HGD than in CA. LOH of p53 was present in HGD (5 of 12) and CA (5 of 7). Of cases with <10% of positive cells, including negative cases, 50% also showed LOH. These results suggest that most cases with prominent p53 overexpression but also significant numbers of cases with weak or negative expression have associated allelic p53 deletion. We conclude that i) immunohistochemical stains but not LOH for p53 correlate with progression of dysplasia to carcinoma, ii) p53 immunohistochemistry appears to more accurately predict biologic behavior of dysplasia and carcinoma in UC compared to allelic deletion studies alone. Further microdissection studies are necessary to evaluate the possibility of different carcinoma risk in patients with low percentage of p53 overexpression and associated LOH.     

Intracellular localization of p53 tumor suppressor protein in gamma-irradiated cells is cell cycle regulated and determined by the nucleus

DNA damage leads to the stabilization of p53 protein and its translocation to the nucleus, resulting in activation or suppression of p53-responsive genes. However, a significant proportion of cell nuclei remain negative for p53 and p53-inducible cyclin-dependent kinase inhibitor p21waf1 after a single dose of gamma-irradiation. Quantitation of DNA content in p53-positive and -negative nuclei 4-6 h after 10 Gy of gamma-irradiation of human breast carcinoma MCF7 cells, fibrosarcoma HT1080 cells, and diploid skin fibroblasts showed that p53 and p21waf1 nuclear accumulation occurs predominantly in the G1 phase and at the beginning of the S phase of the cell cycle. The majority of the nuclei in late S phase and in G2-M phase remained p53- and p21waf1-negative. This suggests that there is a cell cycle window during which p53 can accumulate in the nucleus and activate expression of p21waf1. To determine whether cell cycle-dependent distribution of p53 is caused by cytoplasmic modifications of p53 protein or by properties of the nucleus, p53 localization was analyzed in multinucleated cells obtained by polyethylene glycol-mediated cell fusion. Dramatic differences in p53 accumulation were found among the nuclei in individual multinucleated cells. Distribution of p53-positive and -negative nuclei among the phases of the cell cycle was similar to that observed in a regular cell population. These results suggest that the observed differences in p53 accumulation in the nuclei of irradiated cells are determined by cell cycle-dependent nuclear functions. In contrast to p53, p21waf1 was equally distributed among the nuclei of multinucleated cells regardless of the stage of the cell cycle, indicating that the observed phenomenon is specific for p53.     

p53 expression, DNA content and cell proliferation in primary and synchronous metastatic lesions from ovarian surface epithelial-stromal tumours

The aim of this study was to investigate biological heterogeneity between primary and metastatic ovarian cancer lesions from individual patients as a means of elucidating steps in clinical progression. Cancer tissue from 61 untreated patients with ovarian surface epithelial-stromal tumours was examined. p53 expression detected immunocytochemically by the PAb1801 antibody, DNA content evaluated by flow cytometry, and cell proliferation evaluated as the [3H]thymidine labelling index were investigated in primary tumours and corresponding synchronous metastases. The frequency of p53 positivity was similar in primary (62%) and metastatic (66%) sites, with an agreement between the two lesions from the same patient in 97% of the cases. Similarly, aneuploidy frequency (80%) and DNA indices were superimposable in primary and metastatic lesions from the same patient, with a 94% agreement. The frequency of aneuploidy was higher in p53-positive than in p53-negative lesions. An overall poor agreement (rs = 0.44) was observed for proliferative activity of primary and metastatic lesions, due to a heterogeneous profile in omental with respect to primary tumours, which was mainly evident in p53-positive cancers. Conversely, cell proliferation of peritoneal, abdominal and pelvic lesions was qualitatively similar to that of the primary tumour in 88% of patients.     

Apoptosis-related factors p53, Bcl2, and Bax in neuroendocrine lung tumors

Neuroendocrine (NE) lung tumors comprise four classes of progressive aggressiveness for which proliferation and apoptosis rates could both contribute to their distinctive behavior. As p53 mutations may favor escape from apoptosis through changes in Bcl2-Bax expression balance, which are survival and apoptotic genes, respectively, we studied 121 NE lung tumors (16 typical carcinoids (TC), 5 atypical carcinoids (AC), 29 large-cell NE carcinomas (LCNECs), and 71 small-cell lung carcinomas (SCLCs) using immunohistochemistry. We quantified apoptosis by terminal-deoxynucleotidyl-transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL) in 31 of these cases. There was a significant increase of p53 mutant immunophenotype (defined as immunoreactivity with at least two antibodies for at least 20% of tumor cells) between atypical/typical carcinoids group and the LCNEC/SCLC group (P = 0.0003). There was an inverse correlation (P < 0.0001) between the scores of Bax and Bcl2 expression in individual tumors and a significant inversion of the Bcl2. Bax ratio between low-grade (typical and atypical carcinoids) and high-grade (LCNECs and SCLCs) tumors with a predominant Bax expression in the first group and predominant Bcl2 expression in the second. Whereas carcinoids had variable apoptotic indexes, LCNECs had high indexes (1.3 to 6.8%), Bcl2 overexpression, Bax down-regulation, and Bcl2.Bax ratio > 1 correlated with lower apoptotic index in both LCNEC and the pool of LCNECs and SCLCs (P < 0.05) and a lower survival rate in the group of atypical and typical carcinoids and LCNECs (P < 0.002). The highest levels of Bcl2 expression and Bcl2.Bax ratios were associated with p53 mutant immunophenotype (P = 0.02). Our results suggest that aggressiveness in NE lung tumors could be linked, in addition to proliferation, to apoptosis-related factors.     

Overexpression of p53 protein and histologic grades of dysplasia in colorectal adenomas

PURPOSE: To clarify the relation between tumor-suppressor gene p53 expression and histologic grades of dysplasia in colorectal adenomas, we performed immunohistochemical analysis in a series of 59 colorectal polyps and 40 advanced carcinomas. METHODS: Adenomatous polyps were stained by hematoxylin and eosin and classified into mild, moderate, and severe dysplasia (intramucosal carcinoma), according to the World Health Organization's classification. RESULTS: p53 was positive in 7.1 percent (2/28) of mild, 29.4 percent (5/17) of moderate, and 62.5 percent (5/8) of severe dysplasia. In submucosal and advanced carcinomas, positivity rates were 75 percent (3/4) and 47.5 percent (19/40), respectively. Different staining patterns were found, according to grades of dysplasia. In the adenomas with mild or moderate dysplasia, a few focal crypts showed localized p53-positive staining. Adenomas with severe dysplasia had two different staining types. One was a focal staining type as shown in mild or moderate dysplasia; the other was a diffuse staining type, in which glands with mild or moderate dysplasia, surrounding severe dysplasia area, were also stained. Submucosal and advanced carcinomas showed a strong positive staining in cancer cells only. CONCLUSIONS: Overexpression of p53 protein in adenomas with mild or moderate dysplasia and existence of two types of expression in adenomas with severe dysplasia were observed. These facts suggested the possible existence of different pathways in the adenoma to carcinoma progression.     

Antitumor activity of bax and p53 naked gene transfer in lung cancer: in vitro and in vivo analysis

In vitro and in vivo data have demonstrated that virus-mediated p53 gene transfer can induce active cell death and lung tumor regression. In contrast, the therapeutic potential of bax, another apoptosis-inducing gene, has not been described. We compared p53 and bax cytotoxic effects by transient transfection of an average of 25 +/- 5% of the H-322 and H-358 bronchioloalveolar carcinoma cell lines in vitro. Under these conditions, bax expression killed 70 to 90% of the transfected cells whereas p53 killed only 40% of them. The killing activity of both genes involved apoptosis, as shown by TUNEL staining. Surprisingly, BrdU incorporation indicated that the cells that did resist Bax toxicity were blocked in the pre-S phase of the cell cycle, a result expected for p53 only. In vivo, repeated injections of naked DNA encoding Bax or p53 inhibited the growth of 4-mm preestablished H-322 tumors in nude mice. Growth retardation only, and not inhibition, was observed in H-358, a poorly transfectable and rapidly growing tumor. These results indicate that Bax and p53 share a similar, strong antitumor activity in vivo, even if the former is a more potent inducer of apoptosis in vitro.     

Comparison of bax, waf1, and IMP dehydrogenase regulation in response to wild-type p53 expression under normal growth conditions

Recently, we demonstrated that downregulation of inosine-5'-monophosphate dehydrogenase (IMPD; IMP:NAD oxidoreductase, EC 1.2.1.14), the rate-limiting enzyme for guanine nucleotide biosynthesis, is required for p53-dependent growth suppression. These studies were performed with cell lines derived from immortal, nontumorigenic fibroblasts that express wild-type p53 conditionally by virtue of a metal-responsive promoter. Here, the p53-dependent properties of the original "p53-inducible" fibroblasts are presented in detail and compared to related properties of epithelial cells that also express wild-type p53 conditionally, but by virtue of a temperature-responsive promoter. Both types of p53-inducible cells were designed to approximate normal physiologic relationships between the host cell and the regulated p53 protein. Together, they were used to investigate expression relationships between IMPD and other p53-responsive genes proposed as mediators of p53-dependent growth suppression. In both types of cells, IMPD activity, protein, and mRNA were consistently coordinately reduced in response to p53 expression. In contrast, mRNAs for waf1, bax, and mdm2 showed disparate patterns of expression, being induced in one conditional cell type, but not the other. This distinction in regulation pattern suggests that under normal growth conditions, unlike IMPD downregulation, bax and waf1 induction is not a rate-determining event for p53-dependent growth suppression.     

bcl-2 and p53 immunophenotypes in pre-invasive, early and advanced oesophageal squamous cancer

AIMS: An inverse correlation between bcl-2 and p53 expression has been reported in several types of epithelial tumour. The role of bcl-2 and p53 in the development of oesophageal squamous carcinoma has yet to be established. The expression of bcl-2 and p53 proteins has been evaluated in the multistage oesophageal tumorigenesis, which progresses from normal mucosa to dysplasia (squamous intraepithelial lesion, SIL), to invasive early and advanced oesophageal squamous cancer. METHODS AND RESULTS: Sixty-four cases of squamous oesophageal cancer, coexisting with SIL in 18 cases, were immunohistochemically analysed for any overexpression of bcl-2 and p53 proteins. Any association of bcl-2 and p53 protein expression with patient survival was also analysed. We observed bcl-2 expression that decreased significantly during the progression of oesophageal carcinogenesis. A decreasing frequency in the expression of bcl-2 in advanced oesophageal squamous cancer coincided with frequent p53 overexpression. bcl-2 expression was correlated with patient survival by univariate analysis. The association disappeared after adjusting for tumour stage, p53 overexpression showed no association with patient survival by either univariate or multivariate analysis. CONCLUSIONS: The down-regulation of bcl-2 and upregulation of p53 in advanced oesophageal squamous cancer suggest that bcl-2 and p53 proteins may interact in the progression of oesophageal squamous cancer.     

A high prevalence of p53 mutations in pre-malignant oral erythroplakia

Oral squamous-cell carcinoma is thought to be preceded by a number of precursor stages which induce morphological changes in cells of the oral mucosa resulting in clinically detectable pre-malignant lesions such as erythroplakia or leukoplakia. To better understand the etiology of oral erythroplakia, we have examined the p53 tumor-suppressor gene (exons 5-9) for mutations in 24 oral erythroplakia lesions of varying dysplastic phenotypes by PCR/single-strand conformational polymorphism and direct DNA-sequencing analyses. A total of 12 p53 mutations were detected in 11 of 24 (46%) erythroplakia specimens (one specimen contained two different p53 mutations); 25% were single-base-pair deletions and 33% were either G:C-->T:A transversions or G:C-->A:T transitions. A high prevalence of p53 mutation was observed in all categories of erythroplakia lesions: 33% for mildly dysplastic lesions, 50% for lesions exhibiting moderate to severe dysplasia and 50% for lesions that were carcinoma in situ. Although the combined prevalence of p53 mutations observed in erythroplakia was significantly higher (p = 0.02) than that observed earlier for leukoplakia, the prevalence of p53 mutations was similar in erythroplakia and leukoplakia specimens from smokers. The prevalence and spectrum of p53 mutations observed in this series of erythroplakia lesions are similar to those observed for oral squamous-cell carcinoma. These results indicate that mutations of the p53 gene may be linked to the high malignant potential of erythroplakia and provide further evidence that p53 mutation may be an early event in the genesis of oral squamous-cell carcinoma.     

Cooperative effects of p53 and pRB alterations in primary superficial bladder tumors

Altered patterns of p53 and pRB expression have been reported to be frequent events and to have prognostic significance in bladder cancer. To assess the potential adverse consequences of having altered patterns of both p53 and pRB proteins in patients with bladder neoplasms compared with having one or neither abnormality, we have studied a cohort of superficial transitional cell carcinomas of the urinary bladder by immunohistochemical analysis. The present study included 59 well-characterized superficial transitional cell carcinomas (Ta, n = 28; T1, n = 31) for which clinicopathological variables were available. Nuclear overexpression of p53 was identified in 22 cases (37%). A statistically significant association was observed between the p53-positive phenotype and disease progression (P < 0.001), as well as reduced survival (P < 0.001). Undetectable levels of pRB were observed in 11 cases (19%). Patients with a pRB-negative phenotype had a more frequent disease progression (P = 0.014) and decreased overall survival (P = 0.014). We also observed a significant association between altered p53 and undetectable pRB expression patterns (P = 0.001). Nine tumors showed both a p53-positive and a pRB-negative phenotype. There was an even more marked increase in progression (P = 0.00005) and decreased overall survival (P = 0.0004) in patients whose tumors had both alterations after controlling for tumor stage, tumor grade, and suspicion of vascular invasion. These data suggest that alterations of p53 and pRB have a cooperative negative effect on both progression and survival in primary bladder cancer. It may be postulated that aberrant p53 and pRB expression deregulates cell cycle control at the G1 checkpoint and engenders tumor cells with reduced response to programmed cell death. The imbalance produced by an enhanced proliferative activity and a decreased apoptotic rate may determine the aggressive clinical course of the bladder tumors harboring both p53 and pRB alterations.     

Adenocarcinoma arising in Barrett's oesophagus: evidence for the participation of p53 dysfunction in the dysplasia/carcinoma sequence

Adenocarcinoma arising in Barrett's oesophagus is often preceded by mucosal dysplasia, but little is currently known about the aetiology or natural history of this dysplasia/carcinoma sequence. To investigate the participation of the tumour suppressor gene p53 in this sequence, an immunohistochemical analysis of p53 protein overexpression, which is known to closely correlate with point mutation of the p53 gene, was conducted in 30 patients with Barrett's adenocarcinoma. Adjacent Barrett's mucosa was dysplastic in 21 (70%) patients. Sixteen (53%) tumours overexpressed p53, 10 of which had adjacent dysplastic Barrett's mucosa. In all 10 patients, this dysplastic mucosa also overexpressed p53, predominantly in areas of high grade compared with low grade dysplasia. In contrast, none of the dysplastic mucosa adjacent to 11 tumours lacking p53 overexpression showed detectable values of p53. These results suggest that p53 dysfunction may participate in the progression from dysplasia to carcinoma in some patients with Barrett's oesophagus.     

Expression and alteration of p53 and p21(waf1/cip1) influence the sensitivity of chemoradiation therapy for esophageal cancer

BACKGROUND/AIMS: In vitro analyses have been demonstrated that wild type p53 and p21(waf1/cip1) proteins regulate cellular proliferation and sensitivity of anticancer agents, however, the roles of p53 and p21(waf1/cip1) expression on the response to the chemoradiation therapy for human esophageal squamous cell cancer have not been investigated. METHODOLOGY: With an immunohistochemical method using specimens before and after the chemoradiation therapy, we investigate in this report the influence of the p53 and p21(waf1/cip1) expression on the chemoradiation therapy response or alteration of these protein expressions by chemoradiation therapy in thirteen esophageal squamous cell cancer patients who received our recently developed chemoradiation therapy. RESULTS: In the biopsy specimens before the chemoradiation therapy, 82% of the responders and 71% of patients with down T-classification had either a p53-/p21+ or p53+/p21+ phenotype. Eighty two percent and 46% of the cases with these two phenotypes showed complete or partial response and down T-classification, respectively. After the chemoradiation therapy, 73% of the responders and 71% of the patients with down T-classification had either a p53-/p21+ or p53+/p21+ phenotype. Eighty eight percent and 56% of the cases with these two phenotypes showed complete or partial response and down T-classification, respectively. Comparative analysis before and after the chemoradiation therapy revealed that four patients had an alteration of p53 and p21(waf1/cip1) expression in association with the therapeutic response. CONCLUSIONS: These results suggest that wild type p53 or p21(waf1/cip1) expression relates with and can be altered by the chemoradiation therapy, which could influence the therapeutic efficacy.     

Circulating p53 antibodies as early markers of oral cancer: correlation with p53 alterations

p53 aberrations are early events in the pathogenesis of betel- and tobacco-related oral malignancies. Accumulation of p53 protein in oral lesions may elicit a humoral immune response against p53 protein in these patients. p53 antibodies (Abs) were analyzed in 183 sera obtained from patients with premalignant or malignant oral lesions and normal individuals by enzyme-linked immunoassay using recombinant p53 protein as antigen. These results were correlated with accumulation of p53 protein in patients' matched oral tissue specimens. Circulating p53 Abs were observed in 24 of 70 (34%) cancer patients and 15 of 50 (30%) patients with premalignant oral lesions. p53 Abs showed a significant association with increase in tumor size and dedifferentiation of tumors, factors indicative of poor prognosis. Expression of p53 protein was analyzed in 43 matched oral lesions (18 premalignant and 25 malignant cases). All the p53-seropositive patients (7 leukoplakia and 11 squamous cell carcinoma) showed elevated levels of p53 protein in matched oral lesions. However, the total number of patients seropositive for p53 Abs was lesser than that of patients exhibiting p53 protein accumulation in oral lesions. Four of the 63 normal healthy individuals who were heavy consumers of tobacco (smoking/chewing) and betel were found to be positive for p53 Abs. Detection of circulating p53 Abs in patients with premalignant oral lesions suggests that humoral immune response against p53 protein is an early event in oral oncogenesis and may be a surrogate marker for both p53 alteration and preclinical cancer.     

Overexpression of the p53 gene in primary and metastatic head and neck carcinomas

The p53 gene has been correlated with disease progression in a number of human malignancies, and p53 abnormalities are found in a high percentage of head and neck squamous cell carcinomas. The objectives of this study were 1. to correlate p53 expression with disease progression in squamous cell carcinoma of the head and neck (SCCHN), and 2. to determine whether there are site-specific differences in p53 expression. Primary lesions and/or lymph node metastases from 147 patients with invasive SCCHN were immunostained for p53 overexpression. Expression of p53 was similar (42% versus 43%) in primary lesions and lymph node metastases. Expression also did not vary significantly by site in the head and neck. In conclusion, increased p53 expression did not correlate with disease progression in our series of patients with invasive SCCHN. The finding of a lack of increased expression with disease spread to lymph nodes supports the belief that p53 alterations occur early in head and neck carcinogenesis.     

The prognostic significance of accumulation of p53 protein in stage III non-small cell lung cancer treated by radiotherapy

In the present study the prognostic significance of accumulation of nuclear p53 protein on survival and freedom from local progression was investigated. Formalin-fixed, paraffin-embedded sections obtained by bronchoscopy or mediastinoscopy were used to examine the expression of nuclear p53 protein using immunohistochemistry. In 37 cases (57%), overexpression of the p53 protein was detected. No relation was found between p53 expression and other pretreatment variables. Response to radiotherapy was found in 11 p53-negative cases (65%) versus 10 p53-positive cases (42%). Freedom from local progression was significantly better in the p53-negative cases as compared with the p53-positive cases. The p53-negative cases who responded to radiotherapy showed an excellent freedom from local progression rate after 2 years of 100%, whereas all p53-positive cases without response to radiotherapy showed local progression within 24 months. Overall survival between p53-negative and -positive cases did not differ, however the disease-specific survival was found to be worse in the p53-positive cases as compared to the negative cases (median survival 8.4 vs. 14.4 months (P < 0.05)). No correlation was found between p53 expression and the frequency of distant metastases. In conclusion, the results of this study suggest that p53 protein expression may be of prognostic value on freedom from local progression in non-small cell lung carcinoma.     

p53 functional impairment and high p21waf1/cip1 expression in human T-cell lymphotropic/leukemia virus type I-transformed T cells

Human T-cell lymphotropic/leukemia virus type I (HTLV-I) is associated with T-cell transformation both in vivo and in vitro. Although some of the mechanisms responsible for transformation remain unknown, increasing evidence supports a direct role of viral as well as dysregulated cellular proteins in transformation. We investigated the potential role of the tumor suppressor gene p53 and of the p53-regulated gene, p21waf1/cip1 (wild-type p53 activated fragment 1/cycling dependent kinases [cdks] interacting protein 1), in HTLV-I-infected T cells. We have found that the majority of HTLV-I-infected T cells have the wild-type p53 gene. However, its function in HTLV-I-transformed cells appears to be impaired, as shown by the lack of appropriate p53-mediated responses to ionizing radiation (IR). Interestingly, the expression of the p53 inducible gene, p21waf1/cip1, is elevated at the messenger ribonucleic acid and protein levels in all HTLV-I-infected T-cell lines examined as well as in Taxl-1, a human T-cell line stably expressing Tax. Additionally, Tax induces upregulation of a p21waf1/cip1 promoter-driven luciferase gene in p53 null cells, and increases p21waf1/cip1 expression in Jurkat T cells. These findings suggest that the Tax protein is at least partially responsible for the p53-independent expression of p21waf1/cip1 in HTLV-I-infected cells. Dysregulation of p53 and p21waf1/cip1 proteins regulating cell-cycle progression, may represent an important step in HTLV-I-induced T-cell transformation.     

DNA ploidy, P53 expression, and cellular proliferation in normal epithelium and squamous dysplasia of non-cancerous and cancerous human oesophagi

Ki67 expression, S-phase fraction, p53 immunoreactivity and DNA content were examined in morphologically normal mucosa and squamous dysplasia of both cancerous and non-cancerous human oesophagi in order to understand possible early events in the development of esophageal squamous cell carcinoma. 103 different foci from cancerous esophagi including 17 non-pathological epithelium, 10 mild, 17 moderate and 15 severe dysplasia, 14 intraepithelial carcinomas and 30 invasive squamous cell carcinomas were examined. Also studied were 57 biopsy specimens from cancer-free individuals, including 12 normal epithelia, 15 oesophagitis, and 16 mild, 11 moderate and 3 severe dysplasia. Areas of squamous dysplasia from both cancer-free and cancerous oesophagi were morphologically indistinguishable and both demonstrated increased cellular proliferation compared to normal or non-pathological epithelia. However, squamous dysplasia in cancerous oesophagi demonstrated significantly larger ki67 labelling indices and smaller S-phase fractions than dysplasia in cancer-free patients. Squamous dysplasia in cancerous and non-cancerous oesophagi demonstrated an non-diploid DNA histogram in 67.9% and 43.3% respectively. However, dysplasia from cancer-free individuals demonstrated a non-diploid pattern with one or more peaks (Type I non-diploid histogram) and that from oesophageal cancer patients predominantly exhibited non-diploid histograms without any distinctive peaks (Type II non-diploid histogram). Significant differences in the frequency of p53 positive foci were observed between dysplasia of cancer-free (23.3%) and cancerous (56.8%) oesophagi. IN cancerous oesophagi, dysplasia associated with Type II non-diploid histograms had a significantly larger number of p53-positive foci than those with diploid histograms or Type I non-diploid histograms. These results indicated that the biological features of squamous dysplasia were different between cancerous and non-cancerous human oesophagi despite indistinguishable morphological features. In addition, the combination of p53 immuno-histochemistry and DNA ploidy analysis may contribute to identify possible high-risk squamous dysplasia of the oesophagus.     

Assessment of dysplasia, mucosal mucins, p53 protein expression, and DNA content in ulcerative colitis patients with colectomy and ileorectal anastomosis

BACKGROUND: Patients with ileorectal anastomosis after colectomy for ulcerative colitis remain at risk of developing rectal malignancy. Detection of mucosal dysplasia has been used for regular screening but is difficult in inflammatory mucosa, prompting the search for complementary markers. METHODS: This prospective study aimed to assess the prevalence of dysplasia, the predominance of sialomucin, DNA aneuploidy, and p53 overexpression as possible predictors of colorectal tumourigenesis, in the rectal mucosa of an unselected group of 27 patients with ileorectal anastomosis performed for ulcerative colitis. Patients had neither neoplastic nor dysplastic lesions on the colectomy specimen and the retained rectum at the time of surgery. One biopsy specimen of each lateral rectal wall was studied, using routine histology, mucin histochemistry, DNA flow cytometry, and the streptavidin-biotin complex method with D07 monoclonal antibodies directed towards the p53 protein. RESULTS: Seventeen, seven, and three patients showed inflammatory lesions of inactive, moderate, and severe active colitis, respectively. Dysplasia, sialomucin predominance, DNA aneuploidy, and p53 overexpression were not detected. CONCLUSIONS: The risk of malignant transformation of the rectal mucosa after ileorectal anastomosis seemed to be low in this ulcerative colitis group without high-grade dysplasia or carcinoma in the previous colectomy specimen, carefully followed up endoscopically and histologically. It remains to be evaluated which of the methods studied above will optimize the histopathologic surveillance of the rectal mucosa of ulcerative colitis patients with ileorectal anastomosis.