There are instances where doctors have missed lung cancer. Following are the reasons:

1. Reliance on chest X-ray alone
2. Similarity in the incidence of Tuberculosis (TB) and Lung cancer in Singapore
3. Similarity between the X-ray features of TB and lung cancer.
4. Historical belief that if the abnormality is in the upper parts of lungs, it must be TB
5. Misconception that the young people, non smokers, or women hardly get lung cancer.
6. Ignoring the family history of cancer.
7. Premature discharge from the follow-up of very slowly growing cancer. 

Anything that is less than 1 centimetre in diameter is not visible on the chest X-ray. Even if the abnormality is larger than 1 centimetre, the chest X-ray images are not high in resolution and hence not detailed enough. Due to this, any abnormality on the chest X-ray is described in a very non specific terms such as a nodule, a mass, a lesion, a shadow, a consolidation, a cyst, fibrosis, or scarring etc. none of which indicates the exact nature and composition of the abnormality with certainty.

It is common for someone to be told that a chest X-ray is normal only to find out about the cancer months or years later. More than 20% of chest X-rays in people with symptoms of lung cancer have been found to be falsely negative for lung cancer. This can affect chances of survival as lung cancer can double in size in about 5 months changing from an early curable stage to an advanced incurable stage.

The most common disease with which lung cancer gets confused with is Tuberculosis (TB) in Singapore. This is because TB is almost as common as lung cancer in Singapore and Asia—1300 new cases of TB and 1500 cases of lung cancer every year in Singapore. 

They look alike on the chest x ray. TB affects the upper parts of lung and so does lung cancer. The shape & features of the white spot in the lungs caused by TB (cavity) is similar to the appearance of the spot caused by lung cancer. Hence if one is not careful, one may think that he is dealing with TB when actually patient may be having cancer.

This issue is compounded by the fact that the confirmatory result of TB takes 2 months even in this day and age. So if one decides to start a trial of TB treatment while waiting for its confirmation, and if the patient is having cancer all this while, you end up delaying the diagnosis by 2 months which can be detrimental.

In some cases where a person had TB long ago which has been treated and now healed, a lung nodule can be falsely considered a scar from old TB based on the chest X-ray creating a false sense of security when it could actually be lung cancer. 

Younger age group of TB patients, and historical association of smoking with cancer adds to the confusion as it can make doctors think that even if someone has an abnormal X-ray, if he or she does not smoke, or is too young, he cannot be having cancer when the truth is that lung cancer has become more common in non-smokers and affect people as young as 30 year old. 

There is a 50% chance of having a lung cancer if someone’s parents or siblings had it. Hence telling the doctor about such a family history is extremely important. Occasionally people have cancer that is very slow to grow. In such case a person with a lung spot may be discharged from the doctor’s follow-up once the spot has remained stable for some time like 2 years. However, if it is a slow growing cancer, it may show the growth changes after 2 years. 

What can you do? If your chest X-ray is abnormal, feel free to ask your doctor if you need a CT scan for better assessment. Beware that being young or a non-smoker does not mean that one cannot have lung cancer. Take the personal or a family history of cancer seriously and inform your doctor of these.

Normal looking chest X-ray of a patient on the left, whose CT scan (on the right) picked up the nodule (yellow arrow) which turned out to be lung cancer.