In evaluation of someone for lung cancer, a chest X-ray has several limitations. 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.
This is the biggest limitation of the chest X-ray, so much so that “lung specialists” by virtue of being the last line of defence for the patients, do not trust the chest X-ray anymore. This is also because there have been instances where doctors have occasionally missed lung cancer or delayed the diagnosis of lung cancer by relying on the X-rays alone with serious implications to their career.
The most common disease with which lung cancer gets confused 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 the lung cancer. The shape & features of the white spot in the lungs caused by TB (cavity) is often 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.
Younger age group of TB patients, and historical association of smoking with cancer adds to the confusion as it can make doctors think that if patient is young, or does not smoke, 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.
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.
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.
While there have been malpractice litigations against the doctors for such a misdiagnosis or delayed diagnosis, it is the limitations of chest X-rays and lack of awareness of such limitations that is the true reason behind such unfortunate events. What is not visible on the chest X-ray, cannot be diagnosed.
Paradoxically lung cancer is missed in the people in whom it could have been cured if it was detected early. This group of people are those with small size cancer that is not picked up by the chest X-ray, people who have hazy nodules (ground glass) which have higher potential for being cancerous again not picked up by an X-ray, nodule in young people because of the false belief that lung cancer only affects older people, nodules in never smokers because of the notion that lung cancer is only caused by smoking, and women because of the notion that women only get breast or ovarian cancer.
What can you do? Do not rely on the chest X-ray when looking for lung cancer but instead rely on the CT scan.
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.