Search tips
Search criteria 


Logo of nihpaAbout Author manuscriptsSubmit a manuscriptHHS Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
Nutr Cancer. Author manuscript; available in PMC 2010 July 1.
Published in final edited form as:
Nutr Cancer. 2010 May; 62(4): 436–442.
doi:  10.1080/01635580903441204
PMCID: PMC2895459

Calcium, Vitamin D, VDR Genotypes, and Epigenetic and Genetic Changes in Rectal Tumors


Calcium, vitamin D, exposure to sunshine, and vitamin D receptor (VDR) genotypes have been associated rectal cancer. We used data from 750 rectal tumors and 1,205 population-based controls examine associations with TP53, KRAS2, and CpG Island methylator phenotype (CIMP) markers. Rectal tumors were associated with high levels of calcium overall and with TP53 tumor mutations specifically (OR = 0.6, 95% CI = 0.42–0.84). High levels of sunshine exposure had a borderline protective effect for TP53 tumor mutations (OR = 0.78, 95% CI = 0.59–1.03). A mutation at codon 248 was significantly associated with dietary calcium intake (OR = 0.26, 95% CI = 0.09–0.77); having the Ff/ff genotypes of the FOK1 VDR polymorphism significantly increased the odds of a mutation at codon 245 (OR = 4.74, 95% CI = 1.05–21.39); high levels of dietary vitamin D (OR = 3.42, 95% CI = 1.15– 10.17) and the Ff/ff genotypes of FOK1 (OR = 3.34, 95% CI = 1.11– 10.02) and the GA/AA genotypes of the CDX2 VDR polymorphism (OR = 2.85, 95% CI = 1.23–6.58) increased the odds of a TP53 mutation at codon 273. These data support an association between calcium and rectal tumors overall as well as specifically with TP53 mutations. However, given the number of comparisons, findings need to be confirmed in other studies.


Calcium and vitamin D have been associated with both colon and rectal cancer (16). Some studies have suggested that associations with more distal colon and rectal tumors may be stronger than those observed for proximal colon tumors (5,7,8). The vitamin D receptor (VDR) has been shown to modify the associations between diet and colon cancer and colon adenomas (5,911). A study of colon cancer further suggested that the Fok1 and CDX2 VDR polymorphisms (rs10735810 and rs11568820) may be more strongly associated with KRAS2 and possibly CIMP tumors than with TP53 mutated tumors; these associations were modified by use of aspirin/NSAIDs (12) Associations between calcium, vitamin D, sunshine exposure, VDR, and specific mutations in rectal cancer have not been reported. However, given that associations for calcium and vitamin D have been reported as being stronger for more distal and rectal tumors in some studies, it is reasonable to determine if these factors are associated with specific rectal tumor mutations.

In this study, we determined CIMP and TP53 and KRAS2 mutations from 750 incident rectal cancer cases from a population-based study conducted in Northern California and Utah. We limit our analyses to rectal cancer since associations have been previously reported for colon cancer (12). We use a case-control study design utilizing data from 1,205 population-based controls to examine associations between calcium, vitamin D, sunshine exposure, and VDR genotypes.


Participants in the study were from the Kaiser Permanente Medical Care Program of Northern California (KPMCP) and the state of Utah. All eligible cases within these defined areas were identified and recruited for the study. Cases with a first primary tumor in the rectosigmoid junction or rectum were identified between May 1997 and May 2001; tumor blocks were obtained between 2004 and 2007. Case eligibility was determined by the Surveillance Epidemiology and End Results Cancer Registries in Northern California and in Utah. To be eligible for the study, participants had to be between 30 and 79 yr of age at time of diagnosis, English speaking, mentally competent to complete the interview, could not have had previous colorectal cancer (13), and could not have known (as indicated on the pathology report) familial adenomatous polyposis, ulcerative colitis, or Crohn’s disease.

A total of 1,505 rectal cancer cases were identified; of these, 982 were interviewed. Reasons for nonresponse have been detailed (14). Block retrieval involved obtaining biopsy prior to treatment as well as paraffin embedded tissue from the resection. In some instances, because of radiation prior to resection, tissue was limited from the resection; therefore, biopsy specimens were used for making tumor DNA. In Utah, blocks were requested for all cases except those who refused release of blocks. For those who were not interviewed and had not signed a medical record release, the Utah Cancer Registry retrieved the blocks and released them to the study without key identifiers of name, address, and complete date of birth (year and month of birth were released). At the KPMCP, samples were retrieved from persons who signed a consent form or who had died. For the 1,495 eligible rectal cancer cases identified at both centers, 239 people identified with rectal cancer had not given consent to have the tissue released (15.9%); and for an additional 234 cases, either tumor tissue could not be obtained or DNA could not be extracted. Tumor DNA was extracted from 81.4% of all rectal cancer cases identified, of which 750 cases had interview data. Controls were randomly selected from membership lists at KPMCP, social security lists, and driver’s license list (people under 65 yr); 1,205 controls (68.8% of those selected) participated and are included in these analyses.

Genetic Analysis

Tumor DNA obtained from paraffin-embedded tissue was characterized by their genetic profile that include sequence data for exons 5 through 8 or the hotspots of mutations of the TP53 gene; sequence data for KRAS2 codons 12 and 13; and 5 CIMP markers MINT1, MINT2, MINT31, p16, and MLH1. At this time there is no “consensus” as to the appropriate CIMP panel or method of detection. However, we have used our panel to demonstrate significant relationships between CIMP and numerous variables, including cigarette smoking and the BRAF V600E mutation, which were independent of microsatellite instability (15,16). This work has helped to support the legitimacy of the CIMP concept (17). Germline DNA was available from blood drawn at the time of the interview. We assessed three VDR markers including rs11568820 (CDX2), intron 8 Bsm I (rs154410), and the Fok1 (rs10735810) as previously described (10,18,19).

Diet and Lifestyle Data

Trained and certified interviewers collected diet and lifestyle data as previously outlined (20,21). The referent year for the study was the calendar year approximately 2 yr prior to date of diagnosis (cases) or selection (controls). Information was collected on demographic factors such as age, sex, and study center; physical activity as determined by a detailed physical activity questionnaire that obtained information on activity patterns 10 and 20 yr ago as well as activity during the referent year (22,23); body size, including usual adult height and weight 2 and 5 yr prior to diagnosis; cigarette smoking history; family history of colorectal cancer in first degree relatives; and medical and reproductive history including use of hormone replacement therapy. Regular use of aspirin and NSAIDs were obtained from the following question: “Before the referent date, did you ever take aspirin, excluding Tylenol, regularly? Some brand names for aspirin include Anacin, Arthritis Pain Formula, Ascriptin Tablets, Bayer, Buffrin, Empirin, Excedrin, and Vanquish. Before the referent date did you ever take other non-steroidal antiinflammatory drugs or arthritis medicines such as ibuprofen, Motrin, Clinoril, Naprosyn, or Feldene?” Regular was defined as at least 3 times/wk for 1 mo.

Dietary intake was ascertained using an adaptation of the CARDIA diet history (21,24,25). Participants were asked to recall foods eaten, the frequency at which they were eaten, serving size, and if fats were added in the preparation. Nutrient information was obtained by converting food intake data into nutrient data using the Minnesota Nutrition Coding Center (NCC) nutrient database. Additionally participants were asked about dietary supplements used. We determined dietary calcium and vitamin D using amount reported from the diet history questionnaire along with amount obtained from supplements. Assessment of various indicators of calcium and vitamin D showed that the diet plus dietary supplement amount was the most stable variable for both men and women when evaluating associations.

Statistical Analysis

Dietary variables were assessed by sex-specific tertile of intake based on the distribution of the controls for men and women separately. We also assessed differences in association by sex, any use of aspirin or ibuprofen-type drugs within the past 2 yr, and by VDR genotypes. Recent use, within the past 2 yr, of aspirin or ibuprofen-type drugs was assessed since recent use was shown to be a better predictor of rectal cancer risk than any or lifetime use. Previous results for colon cancer have shown that NSAIDs are import effect modifiers of VDR and other diet and lifestyle factors (12,26), thus, we have evaluated the potential effect modification of NSAIDs on the associations reported here.

All statistical analysis was done using SAS version 9.1 (SAS Institute, Cary, NC). Tumors were defined by specific mutations detected as any TP53 vs. no TP53 mutation, any KRAS2 mutations vs. no KRAS2 mutation, or CIMP positive vs. CIMP negative. CIMP positive was defined as at least two methylated markers. For TP53 and KRAS2 mutations, we also examined transversion and transition mutations since specific types of mutations were assessed because other studies have shown specific mutations to have etiologic associations (27,28). For TP53 mutations, we examined the more common point mutations since these have been shown to be uniquely related to dietary factors and colon cancer (27). Population-based controls were used to assess associations for the population overall while examining multiple outcomes defined by tumor status. Multiple logistic regression models were used to compare all interviewed cases, regardless of whether or not tumor tissue was obtained, to controls. A generalized estimating equation (GEE) method was used to assess associations for the population overall comparing specific types of mutations to controls as described by Kuss and McLerran (29). Cases could contribute one to three observations in the multinomial GEE models depending how an individual’s number of tumor mutations (CIMP, KRAS2, TP53). All models were adjusted for age at diagnosis or selection and sex along with other factors that have been shown to be related to colon cancer including body mass index (BMI) in kg/m2, long-term vigorous physical activity, pack-years of cigarettes smoked, dietary calcium, and total energy intake. Additional adjustment for center did not alter results. Interaction was assessed by determining if the interaction term significantly improved the overall fit of the model by comparing a model with the interaction term as an ordered categorical variable to a model without the interaction term using the likelihood ratio test with 1 df. P for trend was assessed over ordered categories of variables; in the instance of genotypes, the trend P value was based on a model that included variant, heterozygote, and wild type, although in some instances, odds ratios are presented for the dominant model.


The distribution of tumor mutations within the study population is shown in Table 1. Eleven percent had a CIMP positive tumor, 28.9% had a KRAS2 mutation, and 48.3% had a TP53 mutation. The majority of both KRAS2 and TP53 mutations were transition mutations.

Description of study population

Dietary plus supplemental calcium reduced risk of rectal cancer overall as well as for all specific tumor mutations with a similar degree of risk reduction (Table 2). There were suggestions that hours of sunshine exposure reduced risk of TP53 mutations, although the association was not statistically significant. VDR was not associated with any specific mutation. None of the study variables were associated uniquely with either transition or transversion mutations (data not shown in Table 2).

Associations between calcium, vitamin D, sunshine exposure and VDR genotypes, and rectal cancer mutaitons

We observed unique associations with specific hotspots of the TP53 gene (Table 3). Assessment of specific mutations for TP53 showed that high levels of calcium had the most protection for point mutations at codon 248. On the other hand, high levels of vitamin D intake were associated with increased risk of having a point mutation at codon 273. Having either the Ff or ff genotype of the Fok1 VDR gene increased risk of a point mutation at codon 245 and 273; having the GA or AA genotype of CDX2 VDR polymorphism increased the odds of having a point mutation at codon 273.

Associations between calcium, vitamin D, sunshine exposure, VDR genotype, and specific p53 mutations

Assessment of interaction between VDR genotype and calcium and vitamin D for TP53 and KRAS2 mutations showed nonsignificant interaction (data not shown in tables). Likewise, interactions between calcium, vitamin D, and VDR genotypes and recent use of aspirin/NSAIDs were not statistically significant. Associations were similar for men and women.


Our data support a significant inverse association between calcium and rectal tumors overall as well as for TP53 tumor mutations specifically. We also observed a trend toward lower risk of a TP53 mutation with increased hours of sunshine exposure. Specific point mutations of the TP53 gene were associated with the Fok1 and CDX2 VDR genotypes.

Many epidemiological studies have shown an association between high levels of dietary calcium intake and reduced risk of colorectal cancer, with stronger effects for more distal colon and rectal cancers and adenomas reported for some but not all studies (7,8,3033). Fewer studies have assessed vitamin D and sunshine exposure with rectal cancer. We have previously reported that both calcium and vitamin D have been associated with reduced risk of rectal cancer and that the association may be modified by VDR genotype. Others have failed to observe a similar association (8). A review of over 60 observation studies likewise did not observe an association between vitamin D and rectal cancer (7). However, studies have not examined associations with tumor markers, and our findings suggest that associations differ by marker examined. However, vitamin D has been shown to reduce rectal cell proliferation (34). A study of Miller and colleagues (35) showed that both calcium and vitamin D were associated with apoptotic score, providing additional evidence for the involvement of calcium and vitamin D in CRC carcinogenesis.

The strongest associations were with TP53 in our study. TP53 is one of the more commonly mutated genes in rectal tumors (36) and is involved in important cellular functions including apoptosis, DNA repair, cell-cycle control, and differentiation (37). Furthermore, specific point mutations such as an arginine residue at codon 248 in the L3 loop of the core domain of the gene is thought to play a critical role in DNA binding; a glycine at codon 245 also in the L3 loop allows the L3 loop to assume unique conformations; arginine at codon 273 in the loop-sheethelix motif (38). Furthermore, mutations in these specific sites have been linked with specific exposures that alter cancer risk. For instance, polycyclic aromatic hydrocarbons and benzo[a] pyrene has been associated with G>T transversions and TP53 mutations at codons 157, 248, and 273 (37,39); aflatoxin has been associated with mutations at codon 249; sunlight exposure has been associated with CC to TT transition mutations (37). Whereas we observed a significant inverse association with TP53 for calcium and sunshine exposure overall, point mutation at codons 245 and 273 were associated with an increased risk of these factors.

This is the largest study to date to report on specific rectal tumor markers and calcium, vitamin D, sunshine exposure, and 3 VDR polymorphisms as they relate to tumor markers. This is 1 of the largest studies of rectal cancer conducted to date, and we were therefore able to look specifically at rectal vs. colorectal cancer. We were able to examine KRAS2, TP53, and CIMP in these rectal tumors in combination with diet and genetic factors. However, although we examined the hot spots of both the KRAS2 and TP53 genes, accounting for most mutations, it is possible that mutations were missed. Likewise, our markers for CIMP have been shown to be associated with cigarette smoking and other factors (27,40,41), but other markers could have expanded our ability to detect associations. There are limitations to our study, including that we have made many comparisons and therefore some findings may be spurious in nature. Additionally, it is important that others confirm these findings in rectal cancer and not just in colon cancer.

Our data add further support for the role of calcium, vitamin D, and the VDR gene in the etiology of rectal cancer. Through our examination of tumor markers, it appears that the pathway associated with calcium, vitamin D, and VDR in rectal tumors is most strongly associated with TP53 mutations. Although these findings are intriguing, it is important that other confirmatory studies be conducted.


This study was funded by grants CA48998 and CA61757 to M. L. Slattery. This research was supported by the Utah Cancer Registry, which is funded by Contract #N01-PC-67000 from the National Cancer Institute, with additional support from the State of Utah Department of Health and the University of Utah, the Northern California Cancer Registry, and the Sacramento Tumor Registry. The contents of this article are solely the responsibility of the authors and do not necessarily represent the official view of the National Cancer Institute. We would like to acknowledge the contributions of Sandra Edwards, Leslie Palmer, and Judy Morse to the data collection and management efforts of this study and to Erica Wolff and Michael Hoffman for genotyping, sequencing, and methylation analysis.


Publisher's Disclaimer: Full terms and conditions of use:

This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden.

The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.

Contributor Information

Martha L. Slattery, University of Utah, Salt Lake City, Utah, USA.

Roger K. Wolff, University of Utah, Salt Lake City, Utah, USA.

Jennifer S. Herrick, University of Utah, Salt Lake City, Utah, USA.

Bette J. Caan, Kaiser Permanente Medical Research Center, Oakland, California, USA.

Wade Samowitz, University of Utah Health Sciences Center, Salt Lake City, Utah, USA.


1. Shin A, Li H, Shu XO, Yang G, Gao YT, et al. Dietary intake of calcium, fiber and other micronutrients in relation to colorectal cancer risk: results from the Shanghai Women’s Health Study. Int J Cancer. 2006;119:2938–2942. [PubMed]
2. Terry P, Baron JA, Bergkvist L, Holmberg L, Wolk A. Dietary calcium and vitamin D intake and risk of colorectal cancer: a prospective cohort study in women. Nutr Cancer. 2002;43:39–46. [PubMed]
3. Kampman E, Giovannucci E, van’t Veer P, Rimm E, Stampfer MJ, et al. Calcium, vitamin D, dairy foods, and the occurrence of colorectal adenomas among men and women in two prospective studies. Am J Epidemiol. 1994;139:16–29. [PubMed]
4. Martinez ME, Willett WC. Calcium, vitamin D, and colorectal cancer: a review of the epidemiologic evidence. Cancer Epidemiol Biomarkers Prev. 1998;7:163–168. [PubMed]
5. Slattery ML, Neuhausen SL, Hoffman M, Caan B, Curtin K, et al. Dietary calcium, vitamin D, VDR genotypes and colorectal cancer. Int J Cancer. 2004;111:750–756. [PubMed]
6. Martinez ME, Jacobs ET. Calcium supplementation and prevention of colorectal neoplasia: lessons from clinical trials. J Natl Cancer Inst. 2007;99:99–100. [PubMed]
7. Huncharek M, Muscat J, Kupelnick B. Colorectal cancer risk and dietary intake of calcium, vitamin D, and dairy products: a meta-analysis of 26,335 cases from 60 observational studies. Nutr Cancer. 2009;61:47–69. [PubMed]
8. Lipworth L, Bender TJ, Rossi M, Bosetti C, Negri E, et al. Dietary vitamin D intake and cancers of the colon and rectum: a case-control study in Italy. Nutr Cancer. 2009;61:70–75. [PubMed]
9. Theodoratou E, Farrington SM, Tenesa A, McNeill G, Cetnarskyj R, et al. Modification of the inverse association between dietary vitamin D intake and colorectal cancer risk by a FokI variant supports a chemoprotective action of vitamin D intake mediated through VDR binding. Int J Cancer. 2008;123:2170–2179. [PubMed]
10. Slattery ML, Herrick J, Wolff RK, Caan BJ, Potter JD, et al. CDX2 VDR polymorphism and colorectal cancer. Cancer Epidemiol Biomarkers Prev. 2007;16:2752–2755. [PMC free article] [PubMed]
11. Wong HL, Seow A, Arakawa K, Lee HP, Yu MC, et al. Vitamin D receptor start codon polymorphism and colorectal cancer risk: effect modification by dietary calcium and fat in Singapore Chinese. Carcinogenesis. 2003;24:1091–1005. [PubMed]
12. Slattery ML, Wolff RK, Curtin K, Fitzpatrick F, Herrick J, et al. Colon tumor mutations and epigenetic changes associated with genetic polymorphism: insight into disease pathways. Mutat Res. 2009;660:12–21. [PMC free article] [PubMed]
13. Slattery ML, Potter J, Caan B, Edwards S, Coates A, et al. Energy balance and colon cancer—beyond physical activity. Cancer Res. 1997;57:75–80. [PubMed]
14. Slattery ML, Edwards S, Curtin K, Ma K, Edwards R, et al. Physical activity and colorectal cancer. Am J Epidemiol. 2003;158:214–224. [PubMed]
15. Samowitz WS, Albertsen H, Herrick J, Levin TR, Sweeney C, et al. Evaluation of a large, population-based sample supports a CpG island methylator phenotype in colon cancer. Gastroenterology. 2005;129:837–845. [PubMed]
16. Samowitz WS, Albertsen H, Sweeney C, Herrick J, Caan BJ, et al. Association of smoking, CpG island methylator phenotype, and V600E BRAF mutations in colon cancer. J Natl Cancer Inst. 2006;98:1731–1738. [PubMed]
17. Issa JP, Shen L, Toyota M. CIMP, at last. Gastroenterology. 2005;129:1121–1124. [PubMed]
18. Slattery ML, Yakumo K, Hoffman M, Neuhausen S. Variants of the VDR gene and risk of colon cancer (United States) Cancer Causes Control. 2001;12:359–364. [PubMed]
19. Sweeney C, Curtin K, Murtaugh MA, Caan BJ, Potter JD, et al. Haplotype analysis of common vitamin D receptor variants and colon and rectal cancers. Cancer Epidemiol Biomarkers Prev. 2006;15:744–749. [PubMed]
20. Edwards S, Slattery ML, Mori M, Berry TD, Caan BJ, et al. Objective system for interviewer performance evaluation for use in epidemiologic studies. Am J Epidemiol. 1994;140:1020–1028. [PubMed]
21. Slattery ML, Caan BJ, Duncan D, Berry TD, Coates A, et al. A computerized diet history questionnaire for epidemiologic studies. J Am Diet Assoc. 1994;94:761–766. [PubMed]
22. Slattery ML, Jacobs DRJ. Assessment of ability to recall physical activity of several years ago. Ann Epidemiol. 1995;5:292–296. [PubMed]
23. Slattery ML, Edwards SL, Ma K-N, Friedman GD, Potter JD. Physical activity and colon cancer: a public health perspective. Ann Epidemiol. 1997;7:137–145. [PubMed]
24. McDonald A, Van Horn L, Slattery M, Hilner J, Bragg C, et al. The CARD IA dietary history: development, implementation, and evaluation. J Am Diet Assoc. 1991;91:1104–1112. [PubMed]
25. Liu K, Slattery M, Jacobs D, Jr, Cutter G, McDonald A, Van Horn L, et al. A study of the reliability and comparative validity of the cardia dietary history. Ethn Dis. 1994;4:15–27. [PubMed]
26. Camp NJ, Slattery ML. Classification tree analysis: a statistical tool to investigate risk factor interactions with an example for colon cancer (United States) Cancer Causes Control. 2002;13:813–823. [PubMed]
27. Slattery ML, Curtin K, Ma K, Edwards S, Schaffer D, et al. Diet activity, and lifestyle associations with p53 mutations in colon tumors. Cancer Epidemiol Biomarkers Prev. 2002;11:541–548. [PubMed]
28. Slattery ML, Curtin K, Anderson K, Ma KN, Edwards S, et al. Associations between dietary intake and Ki-ras mutations in colon tumors: a population-based study. Cancer Res. 2000;60:6935–6941. [PubMed]
29. Kuss O, McLerran D. A note on the estimation of the multinomial logistic model with correlated responses in SAS. Comput Methods Programs Biomed. 2007;87:262–269. [PubMed]
30. Oh K, Willett WC, Wu K, Fuchs CS, Giovannucci EL. Calcium and vitamin D intakes in relation to risk of distal colorectal adenoma in women. Am J Epidemiol. 2007;165:1178–1186. [PubMed]
31. Kampman E, Slattery ML, Caan B, Potter JD. Calcium, vitamin D, sunshine exposure, dairy products, and colon cancer risk (United States) Cancer Causes Control. 2000;11:459–466. [PubMed]
32. Pritchard RS, Baron JA, Gerhardsson de Verdier M. Dietary calcium, vitamin D, and the risk of colorectal cancer in Stockholm, Sweden. Cancer Epidemiol Biomarkers Prev. 1996;5:897–900. [PubMed]
33. Wu W, Willett WC, Fuchs CS, Colditz GA, Giovannucci EL. Calcium intake and risk of colon cancer in women and men. J Natl Cancer Inst. 2002;94:437–446. [PubMed]
34. Thomas MG, Tebbutt S, Williamson RC. Vitamin D and its metabolites inhibit cell proliferation in human rectal mucosa and a colon cancer cell line. Gut. 1992;33:1660–1663. [PMC free article] [PubMed]
35. Miller EA, Keku TO, Satia JA, Martin CF, Galanko JA, et al. Calcium, vitamin D, and apoptosis in the rectal epithelium. Cancer Epidemiol Biomarkers Prev. 2005;14:525–528. [PubMed]
36. Slattery ML, Curtin K, Wolff RK, Boucher KM, Sweeney C, et al. A compromise of colon and rectal somatic DNA alterations. Dis Colon Rectum. 2009;52:1304–1311. [PMC free article] [PubMed]
37. Hussain SP, Harris CC. p53 mutation spectrum and load: the generation of hypotheses linking the exposure of endogenous or exogenous carcinogens to human cancer. Mutat Res. 1999;428:23–32. [PubMed]
38. Cho Y, Gorina S, Jeffrey PD, Pavletich NP. Crystal structure of a p53 tumor suppressor-DNA complex: understanding tumorigenic mutations. Science. 1994;265:346–355. [PubMed]
39. Shen YM, Troxel AB, Vedantam S, Penning TM, Field J. Comparison of p53 mutations induced by PAH o-quinones with those caused by antibenzo[a]pyrene diol epoxide in vitro: role of reactive oxygen and biological selection. Chem Res Toxicol. 2006;19:1441–1450. [PMC free article] [PubMed]
40. Slattery ML, Curtin K, Ma K, Schaffer D, Potter J, et al. GSTM-1 and NAT2 and genetic alterations in colon tumors. Cancer Causes Control. 2002;13:527–534. [PubMed]
41. Slattery ML, Curtin K, Anderson K, Ma KN, Ballard L, et al. Associations between cigarette smoking, lifestyle factors, and microsatellite instability in colon tumors. J Natl Cancer Inst. 2000;92:1831–1836. [PubMed]