Calculating Lung Cancer Risk - Screening Reveals Nodule

How Often Are Nodules Found on Screening CT's Cancerous?

Woman going into a CT scanner
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When lung cancer screening reveals a nodule, what are the chances it is cancer?

The advent of lung cancer screening has the potential to save many lives. But as with a lot of tests, there are often “false positives” something suspicious is found that later on turns out to be nothing. What are the chances that a nodule found on screening is cancer (malignant) and how often are nodules instead benign (non-cancerous?)

First, it’s important to talk about what’s meant by lung cancer screening, as well as a few statistics.

Lung Cancer Screening and Statistics

For a long time, we have hoped for a screening test for lung cancer. After all, we have mammograms to look for breast cancer, pap smears to look for cervical cancer, and colonoscopies to look for colon cancer. The reason is simple. Often (but not always) cancers are most treatable in the early stages of the disease.

That’s certainly true for lung cancer. The survival rate for people with stage 1 lung cancer is roughly 60 to 80 percent. This drops to less than 10 percent for those who are diagnosed with stage 4 of the disease. Unfortunately, a good 40 percent of people already have stage 4 (metastatic) lung cancer at the time of diagnosis. Stage 4 meaning that a cancer has spread to distant regions or the other lung, and is therefore, inoperable. Considering that lung cancer is the leading cause of death for both men and women in the United States that's a big problem.

How Effective Are CT Scans?

But for some people, we now have a screening test. The U.S. National Lung Screening Trial found that screening CT scans (low-dose CT) lowered the death rate from lung cancer by 20 percent when certain individuals have yearly screening low-dose CT scans. This includes people who:

  • Are between the ages of 55 and 74
  • Have at least a 30 pack-year history of smoking, and
  • Continue to smoke, or have quit in the past 15 years.

When counting up numbers, only about 6 percent of people meet the screening guidelines, but it's a start. And with that start comes a few problems. When a nodule is seen on screening — and that's pretty common — what's the chance that it's cancer?

First, it helps to understand how common it is to find nodules on lung CT screening tests. Finding an abnormality on an x-ray or CT of the chest doesn’t necessarily mean cancer. In fact, it’s more likely to be something else — something that you would never know about and would never bother you if you hadn't had the scan.

How Common Are Lung Nodules in People Screened for Lung Cancer?

Since CT screening is relatively new, we haven't known exactly how common nodules are. An estimate found that at least 20 percent of people (individuals who were screened based on the guidelines above) had at least one nodule that required further testing. Here it's important to make a distinction between what a radiologist may call a mass and what she refers to as a nodule. A mass refers to an abnormality greater than 3 cm (about 1 1/2 inches) in diameter.

The term nodule is used to describe abnormalities less than 3 cm in size.

How Often Are Lung Pulmonary Nodules Found on Screening Cancerous?

So if you get that dreaded call, the one in which your doctor says "we found a nodule on your screening CT," how worried should you be?

In the National Lung Cancer Screening trial, between 1 and 4 percent of people required invasive testing to follow-up their CT scans. Among those who had surgery, 25 percent of the nodules turned out to be benign.

Looking at this a different way, In a more recent evaluation researchers looked at people in 2 separate studies.

In one of these (the Pan-American Early Detection of Lung Cancer Study (PanCan,) 7008 nodules were found among 1871 people. Of these 102 were cancerous. In the other (a British Columbia Cancer Agency (BCCA) study,) 5001 nodules were found in 1090 people, with 42 being malignant.

Crunching the numbers, this comes down to 5.5 percent of the people in one study and 3.7 percent in the other who had nodules that turned out to be cancerous.

At this point, it’s important to note that these numbers — the likelihood that a nodule is cancerous —  are for healthy people without symptoms who are being screened. The likelihood of a nodule being malignant may be different for those who have symptoms. It may also be different for those who have a pulmonary nodule on screening but do not meet the criteria noted above.

When is a Nodule More Likely to Be Cancer?

Looking at studies to date, pulmonary nodules found on CT screening were more likely to be cancerous if:

  • They were in the left or right upper lobes, and less likely to be malignant if they were in the right or left lower lobes, or in the right middle lobe.
  • There was speculation of the nodule (meaning that instead of the abnormal area being round, it had spike like areas sticking out from the tumor,) or if the borders were irregular or lobulated.
  • If they were larger.
  • If they occurred in older people more than in younger people.
  • If an individual had a family history of lung cancer.
  • If they occurred in women more often than men.
  • With increasing size of the nodule.
  • In people with a history of emphysema.
  • In people with fewer nodules.

In addition:

  • Part solid nodules were more likely to be cancerous than solid nodules.
  • Solid nodules were more likely to be cancerous than non-solid nodules or nodules with a "ground glass" appearance.

What Is My Nodule If It Isn’t Cancer?

There are many causes of nodules ranging from infections to tuberculosis, to nodules associated with rheumatoid arthritis, and more. The following article discusses several benign and malignant causes of pulmonary nodules.

Calculating Risk

A lung cancer calculator is available for physicians (and the public) to estimate the chances that a nodule found on screening CT is malignant. This Nodule Prediction Calculator was developed based on scientific research, but people are cautioned that it's not a substitute for a physician's advice or treatment. The disclaimer people are asked to read emphasizes a very important point: Not all nodules that are high risk are cancer, and not all nodules that are low risk benign.

Where Do You Go From Here?

If your doctor determines that you have a pulmonary nodule or nodules, there are several approaches she may recommend. These will depend on several things including your risk factors for lung cancer, the appearance of the nodule, the location of the nodule, and your personal preference. Some options may include:


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