A case-control study of smoking and bladder cancer risk: emergent patterns over time.
BACKGROUND
Cigarette smoking is a well-established risk factor for bladder cancer. The effects of smoking duration, intensity (cigarettes per day), and total exposure (pack-years); smoking cessation; exposure to environmental tobacco smoke; and changes in the composition of tobacco and cigarette design over time on risk of bladder cancer are unclear.


METHODS
We examined bladder cancer risk in relation to smoking practices based on interview data from a large, population-based case-control study conducted in Maine, New Hampshire, and Vermont from 2001 to 2004 (N = 1170 urothelial carcinoma case patients and 1413 control subjects). We calculated odds ratios (ORs) and 95% confidence intervals (CIs) using unconditional logistic regression. To examine changes in smoking-induced bladder cancer risk over time, we compared odds ratios from New Hampshire residents in this study (305 case patients and 335 control subjects) with those from two case-control studies conducted in New Hampshire in 1994-1998 and in 1998-2001 (843 case patients and 1183 control subjects).


RESULTS
Regular and current cigarette smokers had higher risks of bladder cancer than never-smokers (for regular smokers, OR = 3.0, 95% CI = 2.4 to 3.6; for current smokers, OR = 5.2, 95% CI = 4.0 to 6.6). In New Hampshire, there was a statistically significant increasing trend in smoking-related bladder cancer risk over three consecutive periods (1994-1998, 1998-2001, and 2002-2004) among former smokers (OR = 1.4, 95% CI = 1.0 to 2.0; OR = 2.0, 95% CI = 1.4 to 2.9; and OR = 2.6, 95% CI = 1.7 to 4.0, respectively) and current smokers (OR = 2.9, 95% CI = 2.0 to 4.2; OR = 4.2, 95% CI = 2.8 to 6.3; OR = 5.5, 95% CI = 3.5 to 8.9, respectively) (P for homogeneity of trends over time periods = .04). We also observed that within categories of intensity, odds ratios increased approximately linearly with increasing pack-years smoked, but the slope of the increasing trend declined with increasing intensity.


CONCLUSIONS
Smoking-related risks of bladder cancer appear to have increased in New Hampshire since the mid-1990s. Based on our modeling of pack-years and intensity, smoking fewer cigarettes over a long time appears more harmful than smoking more cigarettes over a shorter time, for equal total pack-years of cigarettes smoked.
Baris
Dalsu
D
Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Department of Health and Human Services, Bethesda, MD 20852, USA. barisd@mail.nih.gov
Karagas
Margaret R
MR
Verrill
Castine
C
Johnson
Alison
A
Andrew
Angeline S
AS
Marsit
Carmen J
CJ
Schwenn
Molly
M
Colt
Joanne S
JS
Cherala
Sai
S
Samanic
Claudine
C
Waddell
Richard
R
Cantor
Kenneth P
KP
Schned
Alan
A
Rothman
Nathaniel
N
Lubin
Jay
J
Fraumeni
Joseph F
JF
Hoover
Robert N
RN
Kelsey
Karl T
KT
Silverman
Debra T
DT
D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D015994:Incidence; D008281:Maine / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D009513:New Hampshire / Q000453:epidemiology; D016017:Odds Ratio; D018570:Risk Assessment; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects* / Q000453:epidemiology; D016540:Smoking Cessation; D001749:Urinary Bladder Neoplasms / Q000453:epidemiology* / Q000209:etiology*; D014707:Vermont / Q000453:epidemiology