Chest X-Ray for Diagnosis of Lung Cancer

Many people have asked the question, “Can a chest x-ray diagnose lung cancer?” Or instead, you may be wondering about another variety of this question, "If you have a normal chest x-ray but still have a persistent cough, shortness of breath, or pain, could you still have lung cancer?" The quick answer is that between 20 percent and 25 percent of lung cancers may be missed on a chest X-ray, but the role of chest X-rays in diagnosing lung cancer is actually a series of several questions. Let's take a look at what chest x-rays can tell us, what they can't tell us (and how they can miss lung cancer) and what you should know if you are asking one of these questions.

We know that lung cancer survival rates are better the earlier a person is diagnosed. At the same time, roughly half of people are diagnosed when their lung cancer is already considered “advanced stage lung cancer”—cancers which can no longer be cured with lung cancer surgery.

If you are concerned that you may have symptoms of lung cancer, or if you have risk factors for lung cancer, keep reading. Understanding how lung cancer is diagnosed, the limitations of some of the tests used in diagnosis, and being your own advocate could literally save your life.

This is true whether you have smoked for many years or never touched a cigarette. Smoking is the leading cause of lung cancer overall, but lung cancer in never smokers is still the sixth leading cause of cancer-related deaths in the United States. In fact, non-smokers are more likely to have the diagnosis missed and be diagnosed in the later stages of the disease. What does everyone need to know?

Is a Chest X-Ray Enough to Diagnose or Exclude Lung Cancer?

The answer to the question about whether a chest x-ray is enough to diagnose or exclude lung cancer is an emphatic "no." Yet, it’s important to understand why a chest x-ray alone is not enough and the steps that should be taken if you are concerned.

If you have symptoms of or risk factors for lung cancer, a chest x-ray cannot eliminate the possibility that you have lung cancer. This will be discussed in greater detail later on, but it's thought that chest x-rays performed in a primary care setting to look for lung cancer miss nearly 25 percent of lung cancers. Unfortunately, we hear from people with lung cancer very often who were at first reassured that they did not have lung cancer based on the results of a chest x-ray alone, and only later—after their tumor was given more time to grow unchecked—did they receive their diagnosis.

Plain chest x-rays miss a diagnosis of lung cancer far too often. There are surprisingly few recent studies looking at the actual incidence of "missed diagnoses" of lung cancer, but the research that has been done is sobering.

For those who have symptoms of lung cancer, a large 2006 study in the U.K. found that almost 25 percent of chest x-rays done in the primary care setting for patients with lung cancer were negative when performed within a year of diagnosis. Negative chest x-rays occurred in people with all of the most common symptoms of lung cancer with the exception of hoarseness.

Looking at this in a different way, a 2013 review of radiology malpractice suits involving the thorax (the chest cavity), found that at least 40 percent of cases were related to a missed diagnosis of lung cancer.

If lung cancer is missed on a chest x-ray, this could at best delay treatment. At worst, considering the average doubling time of lung cancer is 125 days (and can be as rapid as seven days) the delay in diagnosis could mean the difference between finding cancer in the early stages when surgery is possible and the later stages in which it has become inoperable. And not only are early lung cancers more likely to be curable, but the greatest improvement in survival rates from lung cancer over the last few decades are also among those who have localized (early stage) disease.

If you have symptoms of lung cancer, further testing, often beginning with a CT scan is needed to rule out the possibility of lung cancer.

Why Do Radiologists Sometimes Miss Lung Cancer on Chest X-Rays?

If you or a loved one have had a lung cancer missed on a chest x-ray you're likely asking, "How can that happen?" "How could someone not see cancer on a chest x-ray?" And why are some cancers seen in retrospect, looking back at old x-rays, but not found initially?

It can help to explain a little bit about what radiologists see on a chest x-ray. Chest x-rays are seen as black and white images; physicians are literally looking at shades of gray and shadows. Substances which have a similar density can all look the same. For example, blood, pus (from an infection), and water can all look very similar. In addition, there are many overlapping structures in the chest. Lung tissue behind the collarbone—the clavicle, for instance—can be difficult to visualize.

Other processes in the lungs can further obscure cancer. Pneumonia can "hide" lung cancers and is not uncommonly found hand in hand with lung cancer, as obstruction of the airways from a tumor can lead to pneumonia. Tuberculosis (TB) is a risk factor for lung cancer, but it's not uncommon for lung cancer to be mistakenly diagnosed as TB—they not only look similar on chest x-rays but often have similar symptoms.

In addition, chest x-rays give us information about the structure, but do not tell how an area "functions." An example that is seen often is a "spot" that appears on a chest x-ray after a person has radiation therapy for lung cancer. It is hard to tell on an x-ray (or even CT) if that spot is a new tumor that has appeared, or if it is simply scarring related to the radiation therapy. Thankfully the addition of PET scans has added insight to these questions. A PET scan (which involves the uptake of radioactive sugar by growing cells) can help radiologists see "spots" in the lungs that are actively growing, versus spots which, like scar tissue, are not actively growing.

Finding Cancers on a Chest X-Ray: Why Is It So Hard?

A simple illustration once given in an editorial in the journal Radiology can help explain the difficulty of finding some lung cancers on a chest x-ray.

Have you ever read a "Where's Waldo" book or looked at the "Find the Hidden Picture" illustrations in a copy of "Highlights"? These publications, as well as others which ask you to find the hidden figures in an image, can be used to help explain why finding cancer on a chest x-ray can be so difficult. Though radiologists are experts at finding Waldo on films, some tumors could be equated with the most challenging hidden picture puzzles.

You may have noticed something else if you've worked on a few of these puzzles. Once you've found the hidden picture, you may wonder why it was so hard to find it in the first place. Even if you spent hours working on the puzzle, you may see it immediately, almost glaring at you, once you've solved the puzzle. The same process happens often with chest x-rays. Once the location of a "hidden tumor" is made known, say through a follow-up x-ray or other tests such as a CT scan, the tumor which may not have been seen initially can become glaringly obvious.

In some ways, however, chest x-rays are more difficult to read than the most advanced and challenging hidden picture puzzle. Unlike these puzzles, chest x-rays do not have a key on the side telling you that the object is indeed present somewhere in the picture. In fact, when reading chest x-rays, especially those from people who do not have clear symptoms or risk factors for lung cancer, the chances are that an object (a tumor) is not present and will never be found in the picture (on the films). Statistically, there is not a hidden object to be found.

A final difference between an object on a "Where's Waldo" picture and a chest x-ray are that most hidden picture puzzles are printed in color rather than black and white and shades of gray.

Lest this discussion leave you feeling too discouraged, keep in mind that it is possible to reduce the risk of errors. In one study the most frequent cause of a missed diagnosis of lung cancer was the failure of the radiologist to compare new chest x-ray films to prior films that had been taken. Just as having side by side hidden picture illustrations in which a figure is present in only one makes it easier to find it in the other, having an older film with which to make a comparison lowers the risk of missing a tumor.

When X-Rays Commonly Miss Lung Cancer

There are certain situations in which a cancer is more easily missed on a chest x-ray and this includes anatomic considerations, characteristics of the tumor, and risk factors

Anatomically, cancers in certain parts of the lungs are more difficult to visualize and are more likely to be missed on a chest x-ray. As noted earlier, dense structures such as bone can "hide" small cancers. In fact, in one study, 72 percent of missed lung cancers were in the upper lobes and of these 22 percent were obscured by the collar bones (clavicles.) Cancers found in the periphery of the lungs (such as lung adenocarcinoma) are more commonly missed than those that occur centrally near the large airways (such as small cell lung cancer and squamous cell carcinoma of the lungs.)

There are a few characteristics of lung cancers which also increase the chance of being missed. Size is very important, and tumors smaller than 1.5 centimeters are more likely to be missed than larger cancers. Tumors which have a "ground glass appearance"—something often found with lung adenocarcinomas, also raises the risk that they will not be seen.

Finally, the risk factors a person have for lung cancer may increase the chance that a tumor is missed. Some groups of people tend to fly under a physician's radar screen when it comes to the possibility of lung cancer, and in these people, it's more likely that the diagnosis will be missed. Several studies have found that the diagnosis is often delayed for lung cancer in women relative to men, in non-smokers relative to people who smoke, and among young adults with lung cancer relative to older people. 

Understanding the size of tumors which can be detected is helpful in understanding the limits of scans. As noted above, chest x-rays are more likely to miss lung cancers less than 1.5 cm in diameter. In contrast, a chest CT scan is more accurate down to 1 millimeter (though they can still miss some cancers.)

Researchers in Norway noted the significant difference between chest x-rays and CT scans in finding small lung cancers. Overall they found that the odds of finding these small cancers went from 18 percent on plain x-rays up to 82 percent with ultra-low-dose CT scans.

It's important to take a moment and define some of the confusing terms you may hear when talking about imaging tests of the lungs. Definitions, with links to articles which describe these in greater detail, include:

• Lung nodule: A lung nodule is described as a spot that is 3 cm (1 ½ inches) or less in diameter.
• Lung mass: A lung mass refers to a spot that is greater than 3 cm (1 ½ inches) in diameter or more.
• Shadow on the lung: A shadow on a chest x-ray can mean anything from a tumor to the normal overlap of structures present in the chest.
• Lung neoplasm: The term neoplasm is translated as "new growth" and can be used to describe any form of growth including those that are benign.
• Lung lesion: The term lung lesion simply means an abnormality. It is often used to describe tumors both benign and malignant but can mean essentially anything.
• Benign vs Malignant: Benign tumors can grow quite large and can recur, but do not spread to other parts of the body. Malignant (cancerous) tumors are those that can metastasize.

Just as chest x-rays aren’t sufficient to rule out lung cancer for those who have symptoms, they are not an effective way to screen for lung cancer either. Since some physicians still order chest x-rays for people who have smoked, it’s important to understand why this is the case and what you need to know so that you can be your own advocate in your medical care.

Chest x-rays do sometimes find lung cancer in people with lung cancer who do not have symptoms. In fact, if you talk to lung cancer survivors, a common finding is that they had a chest x-ray done for some unrelated reason and cancer was found. All is well when this is the case, but you cannot depend on a chest x-ray to find cancer.

In the past, physicians sometimes ordered screening chest x-rays for people who had risk factors for lung cancer (and this is still done some places today.) A large study of nearly 150,000 people done in 2011 in which those at risk for lung cancer received annual chest x-rays yearly for four years, found that the screening chest x-rays did not decrease the death rate from lung cancer. Certainly, some cancers were detected, but by the time these cancers were seen on a chest x-ray they were large enough so that life expectancy was the same as it would have been if these people had waited until they had symptoms of lung cancer.

This is not a reason to despair. Unlike chest x-rays, low-dose CT screening can decrease the risk of death from lung cancer (see below).

How Can I Be Screened for Lung Cancer?

Lung cancer screening is now available for those who meet certain criteria. Note that screening refers to the detection of cancer in someone who does not have any symptoms. If you have symptoms, further studies will be needed. Also, keep in mind that everyone is different. Some people who do not meet these criteria may wish to be screened and some people who meet the criteria may not wish to be screened. Used according to these guidelines it's felt that screening could reduce the mortality (death rate) from lung cancer by 20 percent in the United States.

Current criteria for lung cancer CT screening include:

• Being between the ages of 55 and 80
• Having smoked at least 30 pack years
• Those who continue to smoke or quit smoking in the past 15 years
• Those who would be able to undergo treatment if cancer were detected

Lung Cancer Screening in Never Smokers

While recommendations for screening currently include smoking history, we know that never smokers may be at risk due to a family history of the disease, exposure to radon, exposure to occupational substances such as asbestos, air pollution, and more.

A 2018 study published in the Journal of Thoracic Oncology suggests that CT screening in non-smokers may be effective as well. In this study, low-dose CT screening for lung cancer in never smokers helped find a significant number of lung cancers (and at an early stage) that would otherwise have been missed. It's not certain the dangers that would be involved in screening never smokers (such as the risk of causing cancer due to the radiation involved in imaging), but other possibilities, such as liquid biopsies, may offer better methods of screening non-smokers for lung cancer in the future.

What Can You Do Yourself to Avoid a Misdiagnosis or Missed Diagnosis of Lung Cancer?

It can be frightening to hear about the incidence of missed lung cancers on chest x-rays, but this doesn't mean you need despair. As noted above, CT screening can decrease the risk of death from lung cancer among those who have risk factors. Yet even for those without these risk factors, there are several things you can do:

• If you have a chest x-ray, make sure your doctor is aware of—and has available for comparison—any old chest x-rays you have had. As noted above, neglecting to compare new chest x-rays to old is the number one cause of missed diagnoses.
• Make sure that all of your symptoms and risk factors are listed on the order form that the radiologist will see. These essentially give the radiologist a heads up that the "hidden figure" on the "find the picture" is more likely to be present.
• Don't "give up" if you continue to have symptoms of lung cancer such as shortness of breath or a persistent cough. Regardless of the diagnosis, your symptoms deserve an explanation. Further testing will likely be needed. Keep in mind that even CT scans can miss some lung cancers, and testing beyond even a CT scan may be required. If you are still not getting answers, consider getting a second opinion. Sometimes two (or more) minds are better than one.
• See if there is anything you can do to reduce your risk of developing lung cancer.

Bottom Line

Chest x-rays may be helpful in finding a lung cancer but cannot exclude the presence of cancer. In contrast, a normal chest x-ray may convey the false reassurance that everything is okay. Chest x-rays can miss small and potentially curable lung cancers. If you have unexplained symptoms or risk factors for lung cancer, make sure you talk to your doctor.