Enzyme-linked immunosorbent assay for p53 in gastrointestinal malignancy: comparison with immunohistochemistry

In situ quantification of aberrant p53 in colorectal neoplasia

Aberrant p53 protein accumulation was measured immunohistologically in 342 colorectal paraffin-embedded tissue sections from 115 patients (24 with adenocarcinoma, 59 with adenoma and 32 'hospital controls'). Subjective scoring was compared with quantitative cell imaging, including dichotomous (p53+/p53-) status, ng p53mut mg(-1) enterocyte protein, and tumour burden and patient body 'burden' of aberrant p53. A total of 62.5% cancer patients, 23.7% adenoma patients and 3.1% hospital controls were accorded p53+ status on the basis of p53 quantification. Quantitative p53+/p53- assignment had a stronger inverse association with survival (chi2=6.17, p=0.013, Kaplan-Meier test) than subjective 'visual estimation' (chi2=0.57, p=0.449). There was a strong inverse relationship between the p53 'body burden' and the months of post-diagnosis survival (hazard ratio=1.42, p=0.0004, Cox proportional hazards). Absolute quantification for inactivated p53 permits objective and reproducible scoring, adjusts for intra-laboratory immunostaining 'batch effects', corrects for fixation artefacts, and standardizes for inter-laboratory differences in fixation, antibody selection and staining method. Clinically, in situ quantification of p53 will permit more accurate survival prognoses and will inform therapy selection and dose. Ultimately, accurate quantitative tissue/blood p53 correlations may provide a minimally invasive and systemic surrogate measure for these same clinical purposes.

p53, PCNA and Ki-67 expression in oral squamous cell carcinomas: the vagaries of fixation and microwave enhancement of immunocytochemistry

Proliferation markers are widely used as indicators of tumour progression and aggression. Fixation and antigen retrieval methods may enhance the immunocytochemical sensitivity of these markers but may also lead to loss of specificity. As these methods are often used quantitatively, standardisation of internal and external methodology is paramount. This study aimed to compare the effects of alcohol and formalin fixation and of microwaving on the immunocytochemical demonstration of p53, PCNA and Ki-67 in oral squamous cell carcinoma using duplicate tissue blocks from 24 cases. Both qualitative and quantitative differences in antigen expression were revealed. Whilst alcohol fixation alone at least maintained and usually increased the strength of positive staining, microwaving alcohol-fixed sections often gave rise to non-specific staining. p53 staining following microwave enhancement of alcohol-fixed tissue showed a significant incidence of conversion of negative results to positive and of positive staining in unexpected tissue components. Alcohol fixation increased the sensitivity of PCNA detection with a far less dramatic loss of specificity. The results emphasise the need for careful standardisation of immunocytochemical methods, particularly when used quantitatively and for inter-laboratory comparisons.

p53 protein is absent from the serum of patients with lung cancer

p53 protein, which accumulates intracellularly in over half of all human tumours, has also been reported to be present in the sera of patients with various malignancies, including lung cancer. Using a quantitative immunoassay, we measured p53 protein concentrations in 216 sera from 114 lung cancer patients of whom 75 provided matched lung tumour tissues, which were also assayed for p53 protein. p53 protein levels above the detection limit of 0.04 ng ml-1 were detected in only two sera from lung cancer patients (0.14 ng ml-1 and 0.27 ng ml-1), but not in any of 13 sera from non-malignant lung disease patients or in 100 sera from normal non-diseased individuals. The presence of these apparent traces of serum p53 protein concentrations could not be related either to the p53 protein expression status of the primary lung tumours or to the tumour stage, grade or histological type. By pretreating these two sera with anti-p53 antibody linked to solid phase, and by the addition of mouse serum to neutralise possible heterophilic antibodies, the signals arising from these sera were shown to be non-specific and possibly caused by heterophilic antibodies. We conclude that our data do not support previous reports of p53 protein in the sera of lung cancer patients. Since immunoassays are subject to numerous sources of interference in serum, including heterophilic antibodies, we suggest that the results of p53 protein analysis of serum specimens should be interpreted with caution.

Expression of p53 in oesophageal squamous cell carcinoma in Hong Kong Chinese

We studied p53 overexpression in a series of 99 primary oesophageal squamous cell carcinomas (28 well-differentiated, 42 moderately-differentiated and 29 poorly-differentiated squamous cell carcinomas) from Chinese patients using the p53 protein specific mouse monoclonal antibody DO-7 on paraffin sections. The p53 protein was detected in 30% (30 cases) of the tumours. A significantly higher positive rate was noted in the poorly-differentiated tumours (11% for the well-differentiated, 31% for the moderately-differentiated and 48% for the poorly-differentiated tumours). In addition, strong positive p53 staining was identified only in the less differentiated tumour cells in the periphery of the tumour cell nests in all the cases and the expression was weaker in the better differentiated foci. The central keratinizing areas and the immediately adjacent tumour cells were always negative for p53. The adjacent normal oesophageal mucosa was all negative for p53 protein but the non-invasive dysplastic epithelium next to the tumours could also be strongly positive for p53 protein (four out of 14 cases in which the dysplastic epithelium adjacent to the tumour was adequately sampled). In two out of these four cases, the dysplastic epithelium showed staining for p53; even the adjacent invasive tumour was negative for p53. It is concluded that there is a strong relationship between p53 overexpression and tumour cell differentiation in oesophageal squamous carcinoma and overexpression of p53 can occur in non-invasive tumour cells.

Mutant p53 protein overexpression is associated with poor outcome in patients with well or moderately differentiated ovarian carcinoma

BACKGROUND

It has been shown that the p53 gene is mutated in 30-80% of ovarian carcinomas and that the genetic alterations most often manifest as an accumulation of mutant p53 protein in tumor tissue. The prognostic significance of these findings for patients with ovarian cancer, however, must be established clearly.

METHODS

Mutant p53 protein in 90 consecutive epithelial ovarian carcinomas was quantitatively analyzed using a time-resolved immunofluorometric procedure. In contrast to immunohistochemical techniques, this method uses two anti-p53 antibodies. The Cox model was used to evaluate the strength of the associations between the prognostic markers and disease relapse or death at univariate and multivariate levels. Kaplan-Meier survival curves were calculated for patients who were p53-positive or negative and for subgroups with a different clinical stage, histologic grade, or residual postsurgical tumor.

RESULTS

The positivity rates for p53 included 1/21 (5%) with Stage I disease, 1/6 (17%) with Stage II, 29/51 (57%) with Stage III, and 8/12 (67%) with Stage IV (total = 39/90, 43%). Patients with p53-negative tumors had a significantly longer disease free survival than did patients with p53-positive tumors (P = 0.03); these results were similar for overall survival (P = 0.06). Multivariate analysis revealed that the presence of postsurgical residual tumor was the only predictor significantly associated with poor patient outcome. However, when patients were divided into groups based on histologic grade, patients with well (G1) and moderately (G2) differentiated tumors had a significantly higher risk of cancer relapse and death if mutant p53 protein was present in their tumors compared with patients who were negative for mutant p53 protein (< 0.01).

CONCLUSIONS

The immunofluorometric measurement of mutant p53 protein accumulation in epithelial ovarian carcinomas of a low histologic grade was associated significantly with an increased risk for cancer relapse and death. A similar trend also was suggested for early stage disease and in the absence of residual tumor after surgery. These increased risks, however, were not found for patients with high grade or advanced stage cancer or for those with residual tumor. To the authors' knowledge, this is the first report suggesting that p53 tumor protein accumulation is a marker of poor prognosis in a subset of patients with ovarian cancer.