Death by apoptosis is characteristic of cells undergoing deletion during embryonic development, T- and B-cell maturation and endocrine-induced atrophy. Apoptosis can be initiated by various agents and may be a result of expression of the oncosuppressor gene p53 (refs 6-8). Here we study the dependence of apoptosis on p53 expression in cells from the thymus cortex. Short-term thymocyte cultures were prepared from mice constitutively heterozygous or homozygous for a deletion in the p53 gene introduced into the germ line after gene targeting. Wild-type thymocytes readily undergo apoptosis after treatment with ionizing radiation, the glucocorticoid methylprednisolone, or etoposide (an inhibitor of topoisomerase II), or after Ca(2+)-dependent activation by phorbol ester and a calcium ionophore. In contrast, homozygous null p53 thymocytes are resistant to induction of apoptosis by radiation or etoposide, but retain normal sensitivity to glucocorticoid and calcium. The time-dependent apoptosis that occurs in untreated cultures is unaffected by p53 status. Cells heterozygous for p53 deletion are partially resistant to radiation and etoposide. Our results show that p53 exerts a significant and dose-dependent effect in the initiation of apoptosis, but only when it is induced by agents that cause DNA-strand breakage.

A new method for demonstrating antigens in paraffin sections of formol sublimate-fixed tissue is described that utilizes an "indirect" immunohistological technique employing immunoglobulin adsorbed to colloidal gold as the secondary antiserum. The gold particles introduced to antigenic sites are revealed by a silver precipitation reaction. This technique, the immunogold-silver staining method, is of much enhanced sensitivity (up to 200-fold) as corn-''...

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Background and aims: Family history is used extensively to estimate the risk of colorectal cancer but there is considerable potential for recall bias and inaccuracy. Hence we systematically assessed the accuracy of family history reported at interview compared with actual cancer experience in relatives. Methods: Using face to face interviews, we recorded family history from 199 colorectal cancer cases and 133 community controls, totalling 5637 first and second degree relatives (FDRs/SDRs). We linked computerised cancer registry data to interview information to determine the accuracy of family history reporting. Results: Cases substantially underreported colorectal cancer arising both in FDRs (sensitivity 0.566 (95% confidence interval (CI) 0.433, 0.690); specificity 0.990 (95% CI 0.983, 0.994)) and SDRs (sensitivity 0.271 (95% CI 0.166, 0.410); specificity 0.996 (95% CI 0.992, 0.998)). There was no observable difference in accuracy of reporting family history between case and control interviewees. Control subjects similarly underreported colorectal cancer in FDRs (sensitivity 0.529 (95% CI 0.310, 0.738); specificity 0.995 (95% CI 0.989, 0.998)) and SDRs (sensitivity 0.333 (95% CI 0.192, 0.512); specificity 0.995 (95% CI 0.991, 0.995)). To determine practical implications of inaccurate family history, we applied family history criteria before and after record linkage. Only two of five families reported at interview to meet surveillance criteria did so after validation, whereas only two of six families that actually merited surveillance were identified by interview. Conclusions: This study has quantified the inaccuracy of interview in identifying people at risk of colorectal cancer due to a family history. Colorectal cancer was substantially underreported and so family history information should be interpreted with caution. These findings have considerable relevance to identifying patients who merit surveillance colonoscopy and to epidemiological studies.

Two apparently independent mechanisms of instability are recognized in colorectal cancer, microsatellite instability and chromosomal instability. Evidence from colorectal cancer cell lines indicates the presence of either, or both, types of instability in the vast majority. Here, we sought to determine the prevalence of such instability in primary sporadic colorectal cancers. Microsatellite instability was established by demonstration of ovel clonal, nongerm-line alleles in at least two of four tested loci. Chromosomal abnormalities were identified by comparative genomic hybridization (CGH) and flow cytometric analysis of nuclear DNA content. Tumours harbouring chromosomal instability were distinguished from those with stable but aneuploid karyotypes by comparing chromosomal defects at multiple sites throughout each cancer. This analysis allowed assessment of both the number of chromosomal abnormalities and their heterogeneity throughout the tumour. The results confirm that microsatellite instability is consistently associated with multiple, repeated changes in microsatellites throughout the growth of the affected colorectal carcinomas. There were also several carcinomas in which major structural or numerical abnormalities in chromosomes had clearly continued to arise during tumour growth. However, a substantial subset of tumours showed neither microsatellite instability nor multiple, major chromosomal abnormalities. We suggest that the development of a proportion of colorectal cancers proceeds via a different pathway of carcinogenesis not associated with either of the currently recognized forms of genomic instability.