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Smoking contributed to more hepatocellular carcinomas in this Europe-wide cohort than chronic HBV and HCV infections. Heavy alcohol consumption and obesity also contributed to sizeable fractions of this disease burden. These contributions may be underestimates because EPIC volunteers are likely to be more health conscious than the general population.

High levels of the p53 protein are immunohistochemically detectable in a majority of human nonmelanoma skin cancers and UVB-induced murine skin tumors. These increased protein levels are often associated with mutations in the conserved domains of the p53 gene. To investigate the timing of the p53 alterations in the process of UVB carcinogenesis, we used a well defined murine model (SKH:HR1 hairless mice) in (1), and from animal studies it appeared that the UVB part of the solar spectrum is the most carcinogenic (2). This has been substantiated by detection of mutations in the p53 tumor-suppressor gene in human SCCs (3) and basal cell carcinomas (4) that are characteristic for UVB radiation: i.e., mainly C T transitions at dipyrimidine sites among which are CC TT tandem mutations. There are indications that p53 is involved in the earliest stages of human nonmelanoma skin cancer. Recently, it has been reported that p53 mutations are already present in a benign precursor of SCC, actinic keratosis (5), and in skin adjacent to basal cell carcinomas (6). Furthermore, it has been shown that CC --TT tandem mutations in the p53 gene are detectable in biopsies from nonneoplastic skin of sun-exposed sites from Australian skin cancer patients (7).The suspected causal relationship between chronic UV exposure and p53 mutation and their relation to tumor forThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. mation can most directly and unequivocally be established in an animal model in which UV exposure is the only well controlled carcinogenic agent. A robust model is the SKH:HR1 hairless mouse for which the relationship between UVB exposure and carcinogenic response is well established (8, 9) and for which the pathogenesis of UVB-induced SCC shows close similarities with that of human SCC (10).Under physiological circumstances, the wild-type p53 protein has a very short half-life and is present in such small quantities that it is not immunohistochemically detectable (11,12). There are different pathways that lead to accumulation of the p53 protein up to immunohistochemically detectable levels. (i) DNA damage gives rise to a temporary accumulation of the wild-type p53 protein resulting in an arrest of the cell cycle assumed to prevent replication of damaged DNA (13). (ii) Missense mutations in the p53 gene in general lead to a dramatic increase in half-life of the p53 protein (11). In contrast to the transient accumulation of wild-type p53, the latter can lead to a constitutively high p53 level in the cell. We have recently reported that >75% of UVB-induced murine skin carcinomas show immunostaining with the p53-specific polyclonal antiserum CM-5, which was primarily confined to the proliferative compartments of the tumors. A substantial part of the p53-positive staining was associated with point mutations in the conserved domains of the p53 gene (14). Subsequ...

Clusters of p53 immunopositive epidermal keratinocytes (so-called p53 patches, clones or foci) are found in sun or ultraviolet (UV) light-exposed skin. We investigated to what extent these p53 patches are genuine precursors of skin carcinomas in chronically irradiated hairless (SKH1) mice. The mutation spectra of exons 5-8 of the p53 gene of laser-micro-dissected mutant p53 patches and carcinomas were therefore compared. The mutations we found were mainly UV-signature mutations (C-->T and CC-->TT at dipyrimidine sites) located at known hotspots. No significant differences were found between both spectra, indicating that all p53 patches harbour mutations with which they could progress to carcinomas. To examine whether these p53 patches can be used as tumour risk indicators, we made an extensive comparison of the induction kinetics of these patches and carcinomas in genetically modified mice with various defects in nucleotide excision repair (NER), i.e. xeroderma pigmentosum A (Xpa), Xpc and Cockayne syndrome B (Csb) and wild-type mice. In this aforementioned order, the mouse strains developed both p53 patches and carcinomas in the course of daily exposure to 40 J/m(2) UV. Hence, the order in which the NER-deficient mice developed patches was predictive of the order in which they developed tumours. The induction kinetics of the patches in Xpc-deficient mice differed notably from the others: there was a stationary phase (days 13-41) where the numbers were limited to 5-10 patches per mouse before an explosive increase which ran parallel to the other groups. The chance that a p53 patch progresses to carcinoma is relatively small (estimated at 1 out of 8300-40,000/individual when the first tumour appears), but our results are strongly indicative of a causal relationship between p53 patches and carcinomas.

We have investigated UV-B-induced skin tumors of hairless SKH-HRA mice for alterations in the p53 gene and for mutations in either of the three ras genes. Out of 32 tumors screened, only one contained a ras mutation, i.e. in codon 12 of the K-ras gene. Alterations in the p53 gene were much more abundant, as illustrated immunohistochemically by the accumulation of p53 protein in 75% of the tumor sections examined. Immunoreactivity was observed primarily in the proliferative cell compartment, but no clear correlation between p53 staining in tumor cells and histological parameters for malignancy was observed. Subsequent sequence analysis showed that point mutations in the p53 gene are detectable in 30% (nine out of 30) of the skin tumors examined. The majority of the mutations are located in codons 267 and 272, most likely originating from UV-B-induced photo-adducts at dipyrimidine sites in the non-transcribed strand. Codon 272 corresponds to the human codon 278, which is also a hotspot for p53 mutations in human non-melanoma skin cancers. Codon 267 matches the human codon 273, which does not contain a dipyrimidine site, but represents a CpG hotspot for p53 mutations in internal malignancies. Our results demonstrate that this hairless mouse model for UV-induced skin cancer corresponds closely to human non-melanoma skin cancers with respect to mutations in the p53 gene.

In the present study a cancer risk assessment of occupational exposure to cyclophosphamide (CP), a genotoxic carcinogenic antineoplastic agent, was carried out following two approaches based on (1) data from an animal study and (2) data on primary and secondary tumors in CP-treated patients. Data on the urinary excretion of CP in health care workers were used to estimate the uptake of CP, which ranged from 3.6 to 18 micrograms/day. Based on data from an animal study, cancer risks were calculated for a health care worker with a body weight of 70 kg and a working period of 40 years, 200 days a year (linear extrapolation). The life-time risks (70 years) of urinary bladder cancer in men and leukemias in men and women were found to be nearly the same and ranged from 95 to 600 per million. Based on the patient studies, cancer risks were calculated by multiplication of the 10-year cumulative incidence per gram of CP in patients by the estimated mean total uptake in health care workers over 10 years, 200 days a year. The risk of leukemias in women over 10 years ranged from 17 to 100 per million using the secondary tumor data (linear extrapolation). Comparable results were obtained for the risk of urinary bladder tumors and leukemias in men and women when primary tumor data were used. Thus, on an annual basis, cancer risks obtained from both the animal and the patient study were nearly the same and ranged from about 1.4 to 10 per million. In The Netherlands it is proposed that, for workers, a cancer risk per compound of one extra cancer case per million a year should be striven for ("target risk") and that no risk higher than 100 per million a year ("prohibitory risk") should be tolerated. From the animal and the patient study it appears that the target risk is exceeded but that the risk is still below the prohibitory risk.

Associations between polymorphisms in genes (SNPs) involved in the arachidonic acid (AA) pathway and colorectal adenomas have been investigated in a Dutch case control study including 384 cases and 403 polyp-free controls. Twenty-one polymorphisms in seven candidate genes were studied and a potential modifying effect of fish consumption was considered. A protective effect on colorectal adenomas was found for the CT genotype of SNP H477H in PPARgamma and the GC genotype of SNP V102V in COX-2 (OR 0.63, 95% CI 0.45-0.89 and OR 0.65, 95% CI 0.46-0.92, respectively) compared with the homozygous major genotypes. An increase in adenoma risk was observed for the TC genotype of SNP c.2242T-->C in COX-2 (OR 1.47, 95% CI 1.07-2.00) compared with the TT genotype. Analysis with estimated haplotypes confirmed these associations and revealed three additional associations with COX-2, sPLA(2) and 15LOX haplotypes. Fish consumption modified the associations with COX-2 and PPARdelta genotypes. For SNP c.-789C-->T in PPARdelta the major genotype showed a decrease in adenoma risk for those in the highest tertile of fish consumption (T3), as compared with the lowest tertile (T1) (OR 0.65, 95% CI 0.41-1.02). Protective effects were also observed for SNPs V102V and c.2242T-->C in COX-2 and high fish intake. The interaction between fish consumption and c.2242T-->C was statistically significant, with an OR for the TT genotype and high fish consumption of 0.52 (95% CI 0.27-1.01) as compared with low fish intake. These results indicate that SNPs in genes involved in the AA pathway are associated with colorectal adenoma risk. Some of these associations are modified by fish consumption.

Several human and animal studies have shown that n-3 polyunsaturated fatty acids (PUFA) might be associated with a decreased risk, whereas other studies showed that n-6 PUFA may be associated with an increased risk of colorectal cancer. However, results from these studies are not consistent. We evaluated the associations between serum n-3 and n-6 PUFA levels and colorectal adenoma risk in an endoscopy-based case-control study, conducted in The Netherlands between 1997 and 2002. We included 363 cases of colorectal adenomas and 498 adenoma-free controls. Serum fatty acids were measured in cholesteryl esters. Logistic regression models were used to calculate odds ratios (OR), which were adjusted for age, gender and alcohol intake. Total serum n-3 PUFA levels were inversely associated with colorectal adenoma risk, the OR comparing the third tertile with the first tertile was 0.67 [95% confidence interval (CI) 0.46-0.96, p for trend 5 0.03]. Serum eicosapentaenoic acid (EPA; C20:5n-3) and docosahexaenoic acid (DHA; C22:6n-3) and the n-3/n-6 ratio were inversely associated with colorectal adenoma risk, but these were not statistically significant. In contrast, the risk of colorectal adenomas was increased by total n-6 PUFA with an OR of 1.68 (95% CI, 1.17-2.42, p for trend 5 0.006) and by linoleic acid (LA; C18:2n-6) with an OR of 1.65 (95% CI, 1.15-2.38, p for trend 5 0.007). This is the first observational study that simultaneously finds an inverse association of serum n-3 PUFA and a positive association of n-6 PUFA with colorectal adenoma risk.