Tuberculosis and risk of cancer: a Danish nationwide cohort study

Our plain-English summary of Tuberculosis and risk of cancer: a Danish nationwide cohort study, by D.F. Simonsen, D.K. Farkas, M. Søgaard, et al (The International Journal of Tuberculosis and Lung Disease, 2014).

The study

• Authors: D.F. Simonsen, D.K. Farkas, M. Søgaard, C.R. Horsburgh, H.T. Sørensen, R.W. Thomsen
• Journal: The International Journal of Tuberculosis and Lung Disease
• Published: 2014;18(10):1211-9
• Cited by: 36 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives: To investigate the short- and long-term risk of cancer in patients with active tuberculosis (TB).

Design: Using Danish nationwide databases, we quantified cancer risk in TB patients during 1978-2011 compared with the general population.

Results: We observed 1747 cancers in 15 024 TB patients (median follow-up 8.5 years), reflecting a standardised incidence ratio (SIR) of 1.52 (95%CI 1.45-1.59). All-time SIR for extra-pulmonary cancer was 1.29 (95%CI 1.22-1.36) and for lung cancer it was 3.40 (95%CI 3.09-3.74). Absolute cancer risk 3 months after TB was 1.83% (SIR 11.09, 95%CI 9.82-12.48), with highly increased SIRs for malignant pleural mesothelioma (368.4), lung cancer (40.9), Hodgkin's lymphoma (30.6), ovarian cancer (26.4) and non-Hodgkin's malignant lymphoma (23.8). Between the 3-month and 5-year follow-up, the SIR for any cancer was 1.59 (95%CI 1.46-1.72), including 19- and 3-fold increases for malignant pleural mesothelioma and lung cancer. Beyond 5 years, the SIR of cancer was 1.17 (95%CI 1.10-1.25). Elevated long-term risks persisted for haematological (SIR 1.34, 95%CI 1.01-1.74) and tobacco-related cancers (SIR 1.78, 95%CI 1.60-1.97).

Conclusion: TB is a marker of occult lung cancer and several extra-pulmonary cancers. TB also predicts increased long-term risk of cancer, possibly related to chronic inflammation and shared risk factors, including immunosuppression and smoking.

In plain English

This Danish nationwide cohort study was about tuberculosis (TB), not asbestos. It used national registries to follow 15,024 people with a first hospital contact for active TB between 1978 and 2011 and compared their cancer rates with those of the general population. Over a median follow-up of 8.5 years, 1747 cancers occurred against 1149 expected (standardised incidence ratio, SIR, 1.52; 95% CI 1.45–1.59). Risk was highest in the first 3 months after TB diagnosis, with 275 cancers against 25 expected. Malignant pleural mesothelioma occurred in 51 TB patients: 27 within 3 months (SIR 368.4, 95% CI 242.7–536.0), 21 between 3 months and 5 years (SIR 19.61, 95% CI 12.13–29.97), and 3 after 5 years (SIR 1.44, 95% CI 0.30–4.21). Only one of the 51 had an asbestosis diagnosis before TB. The authors concluded that TB is a marker of undiagnosed (occult) lung cancer and several other cancers. They also concluded that it predicts higher long-term cancer risk, possibly through chronic inflammation and shared risk factors such as smoking. They stated that they could not rule out asbestos exposure as an important confounder.

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: Nationwide population-based cohort study using Danish registries. Cancer rates in TB patients were compared with national rates as standardised incidence ratios.
• Who was studied: 15,024 patients in Denmark with a first hospital contact for active TB during 1978–2011 (6596 women, 8428 men; median age 43.4 years), followed for a median of 8.5 years.
• Exposure: The exposure studied was active TB disease (first-time hospital diagnosis), not asbestos. Asbestos exposure was not measured; the only asbestos-related information reported was whether patients had an asbestosis diagnosis before TB.
• Main results:
  • All TB patients, whole follow-up: 1747 cancers observed against 1149 expected, SIR 1.52 (95% CI 1.45–1.59).
  • TB patients, first 3 months after TB diagnosis: 275 cancers against 25 expected, SIR 11.09 (95% CI 9.82–12.48).
  • Malignant pleural mesothelioma in TB patients:
• All years: 51 cases, SIR 15.8 (95% CI 11.8–20.8).
• 0–3 months: 27 cases, SIR 368.4 (95% CI 242.7–536.0).
• 3 months to 5 years: 21 cases, SIR 19.61 (95% CI 12.13–29.97).
• Beyond 5 years: 3 cases, SIR 1.44 (95% CI 0.30–4.21).
  • Only one of the 51 TB patients with malignant pleural mesothelioma had an asbestosis diagnosis before TB. The authors took the high mesothelioma SIRs as supporting an association between TB and malignant pleural mesothelioma.
  • TB patients, first 3 months: lung cancer SIR 40.9 (95% CI 34.0–49.0) and extra-pulmonary cancer SIR 7.09 (95% CI 6.02–8.29).
  • TB patients beyond 5 years of follow-up: SIR for any cancer 1.17 (95% CI 1.10–1.25).
  • TB patients beyond 5 years: tobacco-related cancers SIR 1.78 (95% CI 1.60–1.97).
• The authors' conclusion: The authors concluded that TB is a marker of occult lung cancer and several extra-pulmonary cancers. They also concluded that TB predicts increased long-term cancer risk, possibly related to chronic inflammation and shared risk factors, including immunosuppression and smoking.
• Limitations the authors state:
  • The authors could not rule out asbestos exposure as an important confounder of the TB–mesothelioma association.
  • The authors had no data on tobacco smoking or other individual lifestyle and environmental factors.
  • Cancer initially misinterpreted as TB may partly explain the high short-term risk, particularly for lung cancer, mesothelioma and lymphomas.
  • The authors had no data on microbiological confirmation of TB.
  • Heightened diagnostic activity (surveillance bias) might explain some of the short-term increase.
  • Statistical precision was limited for some rare cancers.

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: Cohort Study, Standardized Incidence Ratio (SIR), Lung Cancer, Pleural Mesothelioma, Ovarian Cancer, Chronic Inflammation.

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