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Regular aspirin use and lung cancer risk
© Moysich et al; licensee BioMed Central Ltd. 2002
Received: 17 October 2002
Accepted: 26 November 2002
Published: 26 November 2002
Although a large number of epidemiological studies have examined the role of aspirin in the chemoprevention of colon cancer and other solid tumors, there is a limited body of research focusing on the association between aspirin and lung cancer risk.
We conducted a hospital-based case-control study to evaluate the role of regular aspirin use in lung cancer etiology. Study participants included 868 cases with primary, incident lung cancer and 935 hospital controls with non-neoplastic conditions who completed a comprehensive epidemiological questionnaire. Participants were classified as regular aspirin users if they had taken the drug at least once a week for at least one year.
Results indicated that lung cancer risk was significantly lower for aspirin users compared to non-users (adjusted OR = 0.57; 95% CI 0.41–0.78). Although there was no clear evidence of a dose-response relationship, we observed risk reductions associated with greater frequency of use. Similarly, prolonged duration of use and increasing tablet years (tablets per day × years of use) was associated with reduced lung cancer risk. Risk reductions were observed in both sexes, but significant dose response relationships were only seen among male participants. When the analyses were restricted to former and current smokers, participants with the lowest cigarette exposure tended to benefit most from the potential chemopreventive effect of aspirin. After stratification by histology, regular aspirin use was significantly associated with reduced risk of small cell lung cancer and non-small cell lung cancer.
Overall, results from this hospital-based case-control study suggest that regular aspirin use may be associated with reduced risk of lung cancer.
Regular use of aspirin and other non-steroidal anti-inflammatory dugs (NSAIDs) has been consistently associated with reduced risk of colorectal cancer and adenoma [1–4], possibly due to NSAID-related inhibition of prostaglandin synthesis, enhancement of cellular immune response, or induction of apoptosis [5–8]. A number of epidemiological studies have investigated the potential protective effect of NSAIDs with respect to other cancer sites. There is some evidence that regular and prolonged NSAID use is associated with reduced risk of cancers of the esophagus [3, 9, 10] stomach [3, 9, 11], ovary [12, 13], and female breast [14–16].
Aspirin use and lung cancer risk – summary of published studies.
Peto et al.
5139 British physicians: aspirin intervention group (n = 3429) vs. placebo group (n = 1710)
Lung cancer death rates lower in aspirin group (7.4/10.000 person years) vs. placebo group (11.6/10.000 person years)
Paganini-Hill et al.
13 987 retirement community residents; 111 lung cancer cases after 6.5 years of follow-up
No evidence of lower incidence of lung cancer among male daily aspirin users (RR = 1.35); Lower incidence of lung cancer among female daily aspirin users (RR = 0.29)
Thun et al.
Cancer Prevention Study II: 635,031 US residents; 6 year follow-up
No evidence of lower mortality from respiratory cancers in association with aspirin use among men; Lower respiratory cancer mortality among women using aspirin 1–15 times/month (RR = 0.73; 95 % CI 0.56–0.97)
Schreinemachers & Everson 
NHANES I follow-up: 12,668 US residents; 189 respiratory cancers after 12.4 years (mean) of follow-up
Significantly lower incidence of lung cancer among men using aspirin in past 30 days (RR = 0.55; 95% CI 0.38–0.81); No evidence of lower lung cancer incidence among women using aspirin (RR = 1.40; 95% CI 0.74–2.66)
Hospital-based case-control study
1110 lung cancer cases; 1181 cancer controls and 4906 non-cancer controls
Non-significant risk reduction associated with aspirin use when case group compared to cancer controls (RR = 0.80; 95% CI 0.60–1.20), but not apparent when compared to non-cancer controls (RR = 1.00; 95% CI 0.70–1.40)
Record-linkage case control study
2560 lung cancer patients and 7643 controls identified from general practice research data base
Non-significant risk reduction associated with 7+ prescriptions of NSAIDs 1–3 years prior to diagnosis (OR = 0.84; 95% CI 0.69–1.02)
Akhmedkhanov et al.
Nested case-control study
81 female lung cancer patients and 808 controls selected from the NYU Women's Health Study
Non significant risk reduction between regular aspirin use and overall lung cancer (OR = 0.66; 95% CI 0.34–1.28); Significant risk reduction between regular use and non-small cell carcinoma of the lung (OR = 0.39; 95% CI 0.16–0.96)
Harris et al 
489 lung cancer patients and 978 screening clinic controls (heavy smokers)
Significant risk reduction among daily aspirin users (OR = 0.32; 95% CI 0.23–0.44); effect seen among men and women
Hospital-based case-control study
868 lung cancer cases and 935 hospital controls with non-neoplastic conditions
Significant risk reduction among regular aspirin users (OR = 0.57; 95% CI 0.41–0.78); effect seen among men and women
The study population included individuals who received medical services at the Roswell Park Cancer Institute (RPCI) between 1982 and 1998, and who agreed to complete a comprehensive epidemiological questionnaire. Informed consent was obtained from all participants. The case group consisted of 868 individuals with primary, incident lung cancer, identified from the RPCI tumor registry and Diagnostic Index. Controls included 935 individuals, randomly selected from a pool of 7957 eligible individuals, who received medical services at RPCI for non-neoplastic conditions. These participants came to RPCI with a suspicion of neoplastic disease, but were not diagnosed with either benign or malignant conditions. The most frequently utilized services among the controls were carried out in the breast clinic (13%), dermatology clinic (12%), gastrointestinal clinic (15%), and sarcoma/melanoma clinic (15%). The remaining controls were seen in a variety of clinics at our institute, including gynecological oncology, hematology, head and neck, radiotherapy, and urology; however the proportion of controls seen at these clinics was less than five percent of all control participants. Controls were frequency matched to cases on sex and five-year age intervals.
All participants completed the Patient Epidemiology Data System (PEDS) questionnaire, which is offered to all new patients as part of the admission process, and is returned by approximately 50 percent of new patients. The 16-page instrument covers information on tobacco and alcohol consumption, family history of cancer, occupational and environmental exposures, reproductive and medical histories, and diet. The instrument also assesses aspirin use relevant to the period prior to the onset of disease. Specifically, the instrument queried: 'If you are currently ill, indicate how often you took these medications before the illness'. Participants provided information on how many times a week and for how many years they took aspirin. Participants who reported aspirin use at least once a week for one year were classified as regular aspirin users. Dosage of use was assessed by comparing participants who were classified as non-users to participants who reported that they had taken aspirin either one to six times per week or seven or more times per week. Duration of use was evaluated by comparing non-users to participants who took aspirin for six months to ten years or more than ten years. We also evaluated a combined measure of dosage and duration by computing tablet years (tablets per day × years of use). Reason for analgesic use was unavailable for these analyses.
Descriptive analyses included Student t-tests of means for cases and controls for continuous variables, and chi square tests for categorical variables. Unconditional logistic regression was used to calculate odds ratios (ORs) and 95% confidence intervals (CIs). ORs were adjusted for potential confounders, including age, education, and packyears of cigarettes smoked. Covariates were only included in the final regression model if they were established risk factors in these data or changed the observed risk estimates by at least 15 percent. Variables that were evaluated but not included in the multivariate model were occupational asbestos exposure, dietary fruit and vegetable intake, and family history of lung cancer. Participants classified as non-users (i.e., those who did not report to have used aspirin at least once a week for at least one year) served as the referent category throughout the logistic regression analyses.
Characteristics of 868 lung cancer patients and 935 hospital-based controls – Roswell Park Cancer Institute, 1982–1998.
Cases (n = 868)
Up to high school
p < 0.001
p < 0.001
p < 0.001
Risk of lung cancer in association with aspirin use – Roswell Park Cancer Institute, 1982–1998.
(n = 868)
(n = 935)
(n = 335)
(n = 358)
(n = 533)
(n = 577)
p = 0.04
p = 0.19
p = 0.006
1–10 years of use
11+ years of use
p = 0.06
p = 0.11
p = 0.01
1–10 tablet years3
11+ tablet years
p < 0.001
p = 0.07
p = 0.004
Risk of lung cancer in association with aspirin use among current and former smokers – Effect of packyears of cigarettes smoked – Roswell Park Cancer Institute, 1982–1998.
Lower tertile of packyear distribution
(1 – 34 packyears)
Middle tertile of packyear distribution
(34.1 – 60 packyears)
Upper tertile of packyear distribution
(60.1 – 260 packyears)
(n = 162)
(n = 288)
(n = 307)
(n = 157)
(n = 336)
(n = 90)
p = 0.02
p = 0.20
p = 0.06
1–10 years of use
11+ years of use
p = 0.01
p = 0.26
p = 0.15
1–10 tablet years3
11+ tablet years
p = 0.006
p = 0.21
p = 0.09
Risk of lung cancer in association with regular aspirin use – Effect of histology – Roswell Park Cancer Institute, 1982–1998.
Controls (n = 935)
Adeno-carcinoma (n = 293)
Adjusted OR1 (95% CI)
Squamous Cell (n = 307)
Adjusted OR1 (95% CI)
Large Cell (n = 122)
Adjusted OR1 (95% CI)
Small Cell (n = 157)
Adjusted OR1 (95% CI)
Controls (n = 935)
Non-Small Cell Lung Cancer3 (n = 711)
Adjusted OR1 (95% CI)
Results from this hospital-based case control study are largely consistent with the existing body of evidence on the association between regular aspirin use and lung cancer risk. All previous studies reported some evidence of reduced risk of lung cancer in relation to use aspirin or other NSAIDs [14, 17–23] . We observed a significant risk reduction among participants defined as regular users in the total sample, as well as among men and women separately. Our data also demonstrated significant risk reductions associated with higher aspirin doses, prolonged duration, and greater tablet years of aspirin use, although significant trends were largely restricted to male participants. We further observed that, after restricting the analyses to current and former smokers, the chemoprotective effect of aspirin was most apparent among individuals in the lower tertile of the packyear distribution. Finally, when we explored this risk association among histological subtypes, significant risk reductions were apparent in when controls were compared to patients with both NSCLC and SCLC.
Although our findings follow the general trend that has been demonstrated in previous investigations, some differences exist. Two cohort studies reported reduced risk among aspirin users among females, but not males [18, 19], while we observed strongest associations for male participants. Another study did not demonstrate a risk reduction among females , whereas we consistently found non-significant risk estimates below unity for female participants. In a recent report based on the NYU Women's Health Study, Akhmedkhanov et al.  reported a significant risk reduction for NSCLC and a more modest, non-significant decease in risk for all histological types of lung cancer. Our data are partly in contrast to these results, in that we observed the most marked reduction for SCLC, but also a significant decrease in risk for all NSCLC subtypes combined.
These discrepancies in results may be partly explained by differences in study designs across studies (i.e., randomized trial , cohort study [14, 18, 19, 22] case-control study [20, 23], or by the vast differences in exposure assessment, ranging from assignment of participants to aspirin intervention group vs. placebo group  over ever use of aspirin in the last 30 days  to having had an NSAID prescription in the past three years .
One of the proposed mechanisms for the chemopreventive properties of aspirin and other NSAIDs points to the observation that NSAIDs inhibit prostaglandin (PG)-endoperoxide synthase (cyclooxygenase) enzymes , of which two forms of similar enzymatic activity exist, COX-1 and COX-2. COX-1 is constitutively expressed and involved in homeostasis ; COX-2 is induced and involved in inflammation [24, 25]. There is evidence from laboratory studies to suggest that the COX-2 pathway may be involved in lung tumorigenesis. Bauer et al.  reported significantly higher levels of COX-2 enzymes in mouse lung tumor tissue compared to normal tissue. It has also been shown that aspirin inhibited nitrosamine induced lung carcinogenesis , and it reduced COX-2 enzyme levels in lung cancer cell lines . Further support for a potential role of the COX-2 pathway in lung cancer development comes from several investigations that demonstrated COX-2 overexpression in human lung tumors, specifically NSCLC [29–32] and precursor lesions . While COX-2 expression was generally shown to be increased in NSCLC and to a much lesser extent in SCLC, the role of COX-2 expression in latter tumor type is difficult to determine, due to the fact that the numbers of SCLC tumors examined in these studies was very small.
Several methodological issues should be considered in interpreting these results. As in all case-control studies, bias could have affected the validity of the current findings. Selection bias is likely to have occurred in this investigation. The lung cancer patient group was restricted to individuals who were treated at RPCI, a large regional cancer treatment center, and are not likely to represent the general population of lung cancer patients in the western New York region. However, it is unlikely that self-reported aspirin use would be different for RPCI patients than from patients treated in different facilities. The use of hospital controls might introduce bias, due to the possibility that some controls were suffering from conditions that would make them more likely to use aspirin . However, greater likelihood of aspirin use in the control group would only have attenuated the true risk estimate, rather than produced spurious associations. In addition, hospital controls were selected from a large pool of eligible participants with a wide variety of non-cancer diagnostic groups, minimizing bias arising from potential overrepresentation of patients with characteristics that may be associated with the exposures. In fact, no significant differences with respect to aspirin use were observed for the most common diagnostic categories among controls. Selection bias may have also been introduced due to the low participation rate in this study. Only about 50 percent of eligible cases and controls agreed to complete the PEDS questionnaire. We have no way of ascertaining whether or not those individuals who refused to complete the instrument differed from participants with respect to aspirin use. Nevertheless, previous studies that utilized the PEDS data base and faced the same methodological issue, consistently replicated established epidemiological associations for a variety of cancer sites, including ovary [34, 35], colon , breast , prostate , and lung . Recall bias is always a problem in case-control studies of cancer. However, in this investigation it may have been less of an issue, due to our use of hospital controls. Further, the questionnaire used in this investigation places no particular emphasis on any specific item. Thus, there is little reason to believe that cases were more motivated than controls to recall aspirin use. Exposure misclassification may also have affected our results, as we based our analyses on self-reported analgesic use and were not able to independently verify this information. Also, the questionnaire did not assess the specific doses of analgesic preparations, such as regular or extra-strength tablets. Further, we did not have detailed information on other NSAIDs that participants may have taken and cannot rule out the possibility that cases may have been more likely to have taken preparations such as ibuprofen or prescription NSAIDs, which would have resulted in an overestimated or entirely spurious results. However, we have no reason to believe that any of these potential sources of misclassification were differential in nature.
In summary, in this hospital-based case-control study of lung cancer, we observed consistent associations between aspirin use and risk, particularly among men. Although a number of epidemiological studies have produced fairly consistent results, none of these investigations has been specifically designed to address this research question. These suggestive findings need to be replicated by a well-designed pharmacoepidemiological study that incorporates the newly introduced NSAID preparations.
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