Drinking and Smoking and Colorectal Cancer - A Population-Based Case-Control Study among NL Residents, 1999-2003

1. Drinking and Smoking and Colorectal Cancer - A Population-Based Case-Control Study among NL Residents, 1999-2003 PhD student: Jinhui Zhao Supervisor: Peizhong Peter Wang Committee: Roy West and Sharon Buehler The Annual Colorectal Meeting, June 16-17, 2008, St John’s, NL

2. Background • Studies on the effects of drinking and smoking on colorectal cancer (CRC) have been inconclusive • One study on smoking and CRC conducted in Montreal did not provide evidence (1995) • One study on drinking and CRC in Montreal men showed OR=2.3 (95% CI:1.4-3.7) of distal colon cancer and OR=1.6 (95% CI: 1.0-2.6) for daily drinkers vs non-drinkers (2002) • Drinking beer showed stronger effect on proximal, distal and rectum cancer than wine and spirits ACM, June 16-17, 2008, St. John's NL

3. Research questions • Incidence rate is high in eastern provinces • Age-standardized rate is highest (83/100,000) in NL males and second highest (51) in NL females • Highest rate of heavy drinkers is 3 territories, NL and NS • Smoking rate in BC, AB, NL and NS exceeded the national average ACM, June 16-17, 2008, St. John's NL

4. Research questions • Drinking and smoking are potential risk factors of CRC? • Subtypes risk of CRC may vary • Effects may vary based on types of beverages and tobaccos (differential brands of beverages and tobaccos • CRC cluster may exist, but has not been taken into account in studies and statistical analyses ACM, June 16-17, 2008, St. John's NL

5. Objective of study • To investigate effects of drinking and smoking on CRC and its subsites • To investigate effects of drinking beer, wine and spirits on CRC and its subsites • To investigate effects of smoking cigarette, cigar and pipe on CRC and its subsites • Evaluate validity of reliability of self-reported lifetime drinking and smoking • Investigate non-participation bias of CRC cases ACM, June 16-17, 2008, St. John's NL

6. Research methods-designs • Case-control study for effect of drinking and smoking on CRC • Comparison of characteristics of CRC participants with non-participants • Annul ethanol litres and annual cigarettes and cigarette packs per control compared to 1996 and 2001 alcohol and tobacco sale data by Statistics Canada for validity • Cronbach’s alpha for internal reliability ACM, June 16-17, 2008, St. John's NL

7. Research methods-analyses • Binary multilevel logistic model for all CRC cases to controls • Multinomial multilevel logistic model for colon, rectum cancer cases to controls • Multinomial multilevel logistic model for survival, died cases to controls • Multinomial multilevel logistic model for CRC at stage I-II, III-IV to controls ACM, June 16-17, 2008, St. John's NL

8. What do we find?-non-response bias • 59.94% eligible CRC cases and 44.76% eligible controls participated in the study • Cases aged 20-54 tended to over-represent • Cases aged 65 years old and over tended to under-represent in the participating sample. • Participating rate tended to decrease with an increase in TNM stages • The most serious cases tended to under-represent in the participating sample • The deceased tended to be included in the study ACM, June 16-17, 2008, St. John's NL

9. What do we find?-reliable self-report • Self-reported substance uses are reliable: • Reliability of self-reported drinking: • Internal reliability of all constructed alcohol-items is high, with • Cronbach α = 0.9144 (70+ is acceptable) • Reliability of self-reported smoking • Internal reliability of all constructed tobacco-items is high, with • Cronbach α = 0.8966 (70+ is acceptable) ACM, June 16-17, 2008, St. John's NL

10. What do we find?-valid self-report • What did CRC cases and controls drink? ACM, June 16-17, 2008, St. John's NL

11. What do we find?- valid self-report • What did a Canadian drink? ACM, June 16-17, 2008, St. John's NL

12. What do we find?-valid self-report • How much did a CRC case and control drank per year? ACM, June 16-17, 2008, St. John's NL

13. What do we find?-valid self-report • How much did a Canadian drink? ACM, June 16-17, 2008, St. John's NL

14. What do we find?-valid self-report • What and how much did a CRC case and control smoke? ACM, June 16-17, 2008, St. John's NL

15. What do we find?-valid self-report • How much did a Canadian smoke? ACM, June 16-17, 2008, St. John's NL

16. What do we find?-effects of drinking • Drinking shows weak protective effect on CRC risk • 42% lower risk of CRC for drinking 1-19 years vs never drinker (OR: 0.58, 95% CI: 0.37-0.91) • 43% lower risk of CRC for drinking beer 1-19 yrs vs no (OR: 0.57, 95% CI: 0.36-0.92) • 1-2 drinks of beer decreased by 33% CRC risk compared to no (OR: 0.67, 95% CI: 0.47-0.96) • 42% lower risk of CRC for drinking liquor 1-19 years vs no (OR: 0.53, 95% CI: 0.35-0.80) ACM, June 16-17, 2008, St. John's NL

17. What do we find?-beer & liquor • Drinking shows weak protective effect on risk of rectum cancer but not colon cancer • Drinking shows weak protective effect on risk of died CRC, but not survival CRC • Drinking shows weak protective effect on risk of CRC at stage III-IV, but not CRC at stage I-II ACM, June 16-17, 2008, St. John's NL

18. What do we find?-effects of smoking • Cigarette smoking increased CRC risk (OR & 95% CI) ACM, June 16-17, 2008, St. John's NL

19. What do we find?- effects of smoking • CRC risk increased with smoking cigarette years, number of cigarettes per day, cigarette pack years, and years since cigarette commencing • CRC risk decreased with years of abstention from smoking cigarettes • CRC risk associated with age of initiation of smoking greater than 16 years old ACM, June 16-17, 2008, St. John's NL

20. What do we find?-effects of smoking • Smoking increased CRC risk of males, but females • Smoking increased CRC risk of drinkers, but not non-drinkers • Smoking shows stronger effect on rectum than colon cancer • Smoking shows stronger effect on died CRC than survival CRC • Smoking shows stronger effect on CRC at stage III-IV than CRC at stage I-II ACM, June 16-17, 2008, St. John's NL

21. In summary • Non-participation bias: low participation rate among eligible cases & controls might bias the estimates to be generalized to wide population, but it seems unlikely that the bias would be substantial enough to account for the main results • Validity and reliability of self-reported drinking and smoking: accurate and reliable ACM, June 16-17, 2008, St. John's NL

22. In summary • Drinking shows weak protective effect on CRC. • Smoking cigarettes significantly increased CRC risk • CRC risk increased with smoking cigarette years, smoking pack years, daily number of cigarettes, years since cigarettes smoking commencing • Smoking increased CRC risk among males and drinkers • Smoking tended to be stronger effect on rectum cancer than colon, died CRC than survival, and CRC at stage III-IV than I-II ACM, June 16-17, 2008, St. John's NL

23. What shall we do next? • Regarding the study: • Further studies to evaluate the effects of drinking on CRC among Canadians • Expand studies of smoking and CRC in other provinces • Regarding our study: • Complete my thesis • Complete 3-4 papers for publication • Complete one report and submit to NL government and other provinces to share our results • Incorporate alcohol & tobacco sale data into multilevel analysis which will help us to explain effects of alcohol & tobacco use on CRC in Canada ACM, June 16-17, 2008, St. John's NL