Tuberculosis and Lung Cancer

TB and Lung Cancer - Risks, Misdiagnosis, and Effects

abnormal chest x-ray suggesting TB or lung cancer
How is pulmonary tuberculosis (TB) connected to lung cancer?.

Tuberculosis is a big enough problem alone, but learning that it may have a connection to lung cancer adds further concern. Tuberculosis (TB) is a bacteria that affects roughly a third of the population on earth. At the same time, lung cancer is the leading cause of cancer deaths for both men and women worldwide. What is the link between TB and cancer? How often is lung cancer misdiagnosed as TB? And how does a diagnosis of TB affect those living with cancer?

Tuberculosis (TB) and Cancer Risk – The Evidence

The purpose of this article isn’t to discuss statistics, but it’s important to talk about a few terms before talking about the association of TB and cancer. A risk factor is something that someone has or may be exposed to that indicates that they may be at a higher risk of getting a disease. It is another step to say that something causes cancer.

Many of the studies we look at talk about correlation or association. But correlation doesn’t necessarily mean causation. An amusing example is that of pirates and global warming. There is a correlation between the number of pirates and global warming over time. That, however, doesn’t mean that pirates are responsible for global warming. When two or more things are correlated there could be other variables that are responsible for causation—for example, something that causes both of the diseases that have been correlated.

TB and Risk of Lung Cancer

Several studies have found an increased risk of lung cancer in those who have TB. A large Chinese study of over 700,000 people found that those who had TB were 11 times more likely to develop lung cancer than those without TB. For those who also had COPD, the risk was 16 times higher.

Other studies in Taiwan and Korea have also found that TB appears to be an independent risk factor for lung cancer, though the relative increase in risk wasn’t as high.

It appears that TB may be correlated with particular types of lung cancer, though results vary. One study found that TB is associated with an increased risk of lung adenocarcinoma, but not squamous cell carcinoma or small cell lung cancer. Another study found the only increase in risk was in squamous cell carcinoma in male smokers.

Does TB as a Cause of Lung Cancer Make Sense?

For those of us living in the United States, we don’t always think of infections as having the potential to cause cancer. It’s felt that only about 10 percent of cancers in the US are caused by infectious agents, such as HPV (human papillomavirus, HIV, and hepatitis C. But worldwide, infections are considered the cause of roughly 25 percent of cancers. But how could an infection with TB lead to cancer?

It’s been proposed that the chronic inflammation caused by TB causes DNA damage in cells, which eventually leads to the formation of cancer.

A few findings support this. Lung cancer in those who have had TB tends to occur in the same lobe of a lung that was affected by TB. Lung cancer often arises near the edge of scars left by TB. But whether TB is the cause of lung cancer is still uncertain.

Instead of causation, it could be that certain conditions predispose people to developing both cancer and tuberculosis.  These factors could include smoking, but also conditions which cause the immune system to work improperly (immunosuppression.)

Tuberculosis (TB) and the Risk of Other Cancers

In the past, there have been case reports of cancers other than lung cancer that may be associated with tuberculosis. Knowing this, researchers looked at people diagnosed with TB and cancer in Taiwan. Overall, those with TB were diagnosed with almost twice as many cancers as those without TB.

For men, within 1 year after diagnosis, there was an increased rate of diagnosis of cancers of the head and neck, esophagus, colon, lung, liver, and more than the expected diagnoses of melanoma and Hodgkin’s disease. Beyond 1 year, men with TB were more likely to develop liver, biliary, lung, and bladder cancers. For women, there was an increased rate of leukemia, esophageal cancer, and lung cancer in the first year following a TB diagnosis, with only leukemia remaining higher than the general population after the first year.

A recent study of over 15,000 people with tuberculosis found that, overall, 1.29 percent also had cancer outside of the lungs, and 3.4 percent had lung cancer. This was broken down as follows:

3 months after diagnosis:

  • The overall risk of cancer was 1.83 times more than average
  • The risk of malignant pleural mesothelioma was 368.4 times the average risk
  • The risk of lung cancer was 40.9 times average risk
  • That of Hodgkin's lymphoma was 30.6 times normal
  • Ovarian cancer was 26.4 times the average
  • Non-Hodgkin's lymphoma was 23.8 percent more than normal

Between 3 months and 5 years following diagnosis:

  • The risk of any cancer was 1.59 times normal
  • The risk of mesothelioma was 19 times greater than normal
  • The risk of lung cancer was 3 times more than average

Beyond 5 years:

  • The overall risk of any cancer was 1.17 times normal
  • Persistent increases in risk were found for blood-related cancers (1.34 times normal) and tobacco-related cancer (1.78 times normal)

The conclusion was that tuberculosis is a marker of underlying lung and other cancers, and in addition, is a predictor of long-term risk of cancer.

Misdiagnosis – When is it TB and When is it Lung Cancer?

Recently, it’s been found in countries like India, that lung cancer is often mistakenly diagnosed as TB. This can result in a delay in diagnosis and ultimately a delay in treatments for lung cancer.

Why? Both TB and lung cancer can have similar symptoms; a chronic cough, coughing up blood, unexplained weight loss, and shortness of breath. TB and lung cancer may also appear similar on a chest x-ray.

A lack of awareness and socioeconomic reasons have been cited as causes for these misdiagnoses. While economic reasons are a difficult global problem, a lack of awareness is something that can be addressed fairly easily. What can be done? It’s been noted that in many people who are misdiagnosed, an accurate diagnosis of TB has not been made. Properly diagnosing TB before treatment is, therefore, important. When possible economically, further testing for lung cancer with tests such as CT scans and bronchoscopy is also important.

Effect of Tuberculosis on People with Lung Cancer

Studies looking at the effect of TB on those with lung cancer have revealed mixed results. One small study found that the clinical course—how people responded to treatment and how long they lived—wasn’t changed by TB. Not surprisingly other studies have found that TB worsens the course for those with lung cancer. In one study, survival was almost a year shorter for those who had TB along with lung cancer. Survival also seems to be shorter in those who have TB at the time of diagnosis than in those who develop TB after their lung cancer diagnosis.

A 2016 review did find that, after 3 weeks of treatment prior to surgery, the risk of complications after surgery for lung cancer was no higher in people with tuberculosis than it was for those without the disease.

What Can We Do With This Knowledge?

TB appears to be a risk factor for lung cancer, but whether or not it is the cause is still uncertain. Until we know more:

  • Those who have had TB may want to talk to their doctors about lung cancer screening. CT screening for lung cancer has been found to reduce lung cancer deaths for people between the ages of 55 and 74 who have at least a 30 pack-year history of smoking. Outside of these criteria, people may want to work with their doctors to schedule screening for risk factors other than smoking.
  • Certainly doing everything possible to eliminate other risk factors for lung cancer is important; quitting smoking, checking your home for radon, being aware of occupational causes of lung cancer, and avoiding secondhand smoke may reduce the chance of developing lung cancer even when other risk factors are present.


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