Association of cigarette smoking and asbestos exposure with location and histology of lung cancer

Our plain-English summary of Association of cigarette smoking and asbestos exposure with location and histology of lung cancer, by B.W. Lee, J.C. Wain, K.T. Kelsey, et al (American Journal of Respiratory and Critical Care Medicine, 1998).

The study

• Authors: B.W. Lee, J.C. Wain, K.T. Kelsey, J.K. Wiencke, D.C. Christiani
• Journal: American Journal of Respiratory and Critical Care Medicine
• Published: 1998;157(3 Pt 1):748-55
• Cited by: 62 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Prior studies have suggested that lung cancers that arise in association with cigarette smoking favor an upper-lobe location while those associated with asbestos exposure favor a lower-lobe location. An excess of adenocarcinomas has also been reported among cases not exposed to cigarette smoke as well as among those exposed to asbestos. However, these studies typically have not adjusted adequately for potential confounders such as the patient's age, sex, race, or family history of cancer. To better examine the effects of cigarette smoking and asbestos exposure on location and histology of lung cancer, we analyzed data from a large case-control study that included 456 patients with stage I or II lung cancer. Patients with upper-lobe tumors tended to have had more exposure to tobacco as assessed by pack-years smoked (54.7 versus 46.2, p = 0.07) and less time since quitting smoking (3.0 versus 5.5 yr, p = 0.05). In contrast to some prior reports, asbestos exposure was also associated with an upper-lobe location of tumor. Among those with upper-lobe tumors, 14.6% had a history of significant asbestos exposure compared with 5.4% of those with lower-lobe tumors (p < 0.01). The relationship between asbestos exposure and upper-lobe location of tumor was also statistically significant whether stratified by smoking or analyzed by multivariable logistic regression modeling. Adenocarcinomas were more likely among those with less exposure to cigarette smoke based on fewer pack-years smoked (41.5 versus 61.8, p = 0.0001) and more time since quitting smoking (5.0 versus 3.0 yr, p = 0.02). The proportion of patients with significant exposure to asbestos was lower among those with adenocarcinomas but was not statistically significant (9.5 versus 15.3%, p = 0.09). In multivariable logistic regression analysis, longer time since smoking exposure remained a significant predictor of adenocarcinomas (p < 0.02), but history of asbestos exposure did not predict tumor histology. Thus, in patients with lung cancer, both cigarette smoking and asbestos exposure histories favor an upper-lobe location of tumor. Longer time since smoking exposure favors adenocarcinomas, but the history of asbestos exposure does not appear to influence the tumor histology.

In plain English

The authors analyzed 456 patients with newly diagnosed, surgically removed stage I or II lung cancer at Massachusetts General Hospital, Boston, from December 1992 to August 1996. The patients were the case group of a larger case-control study. Tumors were grouped by location (upper lobes versus a lower-lobe group that also included the right middle lobe) and by cell type (adenocarcinoma versus other types). Smoking came from a questionnaire, and asbestos exposure from a job-based exposure index. Significant asbestos exposure was found in 14.6% of patients with upper-lobe tumors, versus 5.4% of those with lower-lobe tumors (odds ratio 3.00, 95% CI 1.28–7.04). After adjustment for age, family history of cancer, smoking status and time since quitting, the odds ratio was 4.66 (95% CI 1.60–13.57). Upper-lobe tumors were also more common among current smokers than nonsmokers. Asbestos exposure was not significantly linked to cell type, either before or after adjustment. The authors concluded that smoking and asbestos exposure were both associated with upper-lobe tumors, and that asbestos did not influence histology. They noted that the study included only operable tumors and did not systematically assess asbestosis.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Analysis of the lung cancer cases from a hospital-based case-control study. Cases were compared with each other by tumor location and histology.
• Who was studied: 456 of 562 eligible patients (81%) with newly diagnosed, surgically resected primary stage I or II lung cancer, seen at the thoracic surgery service of Massachusetts General Hospital between December 1, 1992 and August 15, 1996. Tumor lobe was known for 397 patients and histology for 418.
• Exposure: Asbestos exposure was measured with an index based on asbestos exposure in the New England building construction trades. The index weighted years worked by time period (before 1965, 1965 to 1972, after 1972) and by job type, such as insulation installation and ship building. A score above 20 counted as significant exposure. Fiber types were not specified. Cigarette smoking was measured as pack-years, smoking status and years since quitting.
• Main results:
  • Tumors in the right lower, right middle or left lower lobe were classified as lower-lobe tumors, and tumors in the right or left upper lobe as upper-lobe tumors.
  • Significant asbestos exposure was found in 14.6% of patients with upper-lobe tumors, versus 5.4% of patients with lower-lobe tumors (p less than 0.01; OR 3.00, 95% CI 1.28–7.04).
  • The link between asbestos exposure and upper-lobe location remained after adjustment for age, family history of cancer, current smoking status and time since quitting smoking (OR 4.66, 95% CI 1.60–13.57, p less than 0.005).
  • The share of upper-lobe tumors rose with smoking: 56.5% among nonsmokers, 68.8% among ex-smokers and 75.7% among current smokers (trend p = 0.04). Patients with upper-lobe tumors had smoked a median of 54.7 pack-years, versus 46.2 for those with lower-lobe tumors (p = 0.07).
  • Across the combined smoking and asbestos categories, the share of upper-lobe tumors rose from 54.6% among nonsmokers without significant asbestos exposure to 93.3% among current smokers with significant asbestos exposure (trend p = 0.001).
  • Four patients had a clinical diagnosis of asbestosis. All four had upper-lobe tumors; three had squamous cell carcinomas and one had an adenocarcinoma.
  • Of patients with adenocarcinoma, 9.5% had asbestos exposure, versus 15.3% of patients with other tumor types. The difference was not statistically significant (OR 1.72, 95% CI 0.95–3.12, p = 0.09).
  • In the adjusted model, asbestos exposure did not significantly predict tumor histology (p = 0.33; OR 1.40, 95% CI 0.71–2.72). Longer time since quitting smoking remained a significant predictor of adenocarcinoma.
  • Patients with adenocarcinoma had smoked a median of 41.5 pack-years, versus 61.8 for patients with other tumor types.
• The authors' conclusion: The authors concluded that, in surgical patients with stage I and II lung cancer, both cigarette smoking and asbestos exposure were associated with an upper-lobe tumor location. Absence and cessation of smoking tended to favor adenocarcinoma, but asbestos exposure did not influence tumor histology.
• Limitations the authors state:
  • Only patients with operable (stage I or II) tumors were included. The authors judged this unlikely to bias tumor location, but said it would have affected histology.
  • Few patients had small cell carcinoma, which may have masked a positive association between asbestos exposure and adenocarcinoma.
  • Asbestos-exposed patients were not examined for radiographic or histologic evidence of fibrosis. A link between lower-lobe location (or adenocarcinoma) and asbestos might appear only in people with asbestosis.
  • Patients with upper-lobe and lower-lobe tumors were not entirely comparable. The authors said the differences were not statistically significant and that adjusting for them did not change the results.
  • The adjusted link between smoking and upper-lobe location was of borderline significance, possibly due in part to inadequate study power.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer.

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Histology, Lung Cancer, Adenocarcinoma, Case-Control Study.

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