Lung nodules: What you need to know

Lung nodules — or pulmonary nodules — are small growths that can develop in the lungs. By definition, they are no larger than 3 cm, or about 1.25” across. Anything bigger than that is considered a mass.  

Lung nodules are very common. But most lung nodules are not due to cancer.  

So, why do lung nodules even form? Do they ever cause any symptoms? And, what should you do if you find out you have one? 

Read on to learn the answers to these and other questions about lung nodules. 

How serious is a lung nodule?

The answer to that question depends on the answer to several others.  

• Number: Is there only one, or are there many lung nodules?  
• Size: How big is it/are they? 
• Age: How old are you? 
• Family history: Does any type of cancer run in your family? 
• Medical history: Have you ever had a lung infection? 
• Work history: Have you ever been exposed to asbestos or radon? 
• Social history: Have you ever smoked, vaped or used other tobacco products?  

The older you get, the more common benign — on non-cancerous — lung nodules become, particularly if you live in certain parts of North America. But it’s more concerning if you have many nodules and have had cancer before than if you only have one and have never had cancer.

Anything larger than a green pea (about 5 mm) is worth investigating, but even smaller nodules might call for monitoring. And, answering “yes” to any of the history-related questions above significantly raises the risk that a nodule might be cancerous. 

Why do lung nodules even occur?

People may develop lung nodules for many reasons. These include:  

• Old infections, which can cause scarring 
• Chronic infections, such as tuberculosis 
• Sarcoidosis and rheumatoid arthritis, both autoimmune disorders 
• Prior trauma, such as a gunshot wound or auto accident 
• Cysts, or hollow sacs filled with fluid 

Congenital conditions

• Arterial venous malformation, which shows up as dark spots in the middle of lung 
• Pulmonary sequestration, when a segment of lung has its own blood supply 
• Congenital emphysema, which some babies are born with 

Certain fungal infections

• Blastomycosis (Great Lakes area)
• Coccidiodomycosis or Valley Fever (San Joaquin Valley)
• Histoplasmosis (Mississippi Valley)

Lung nodules may also be cancerous. When that happens, they could either be caused by lung cancer or a different type of cancer that has spread to the lung from another place.  

Unfortunately, the lung is a very common location for metastatic disease. That means many other cancers tend to spread there. Sarcomas, for instance, often spread to the lungs. So does colorectal cancer. But technically, any type of cancer can spread to the lungs. 

How are lung nodules usually found?

There are four main ways: 

1. An X-ray taken for an unrelated reason, such as an auto accident 
2. Imaging related to a lung problem, such as a cough that won’t go away or pneumonia symptoms 
3. A lung cancer screening  
4. A health screening performed before an operation    

A rapid CT scan of the heart called a calcium score test is done to assess coronary artery disease. Sometimes, it catches the edges of the lungs in its field of vision, revealing nodules. Abdominal CT scans can also sometimes catch nodules in the lower third of the lungs. 

Do lung nodules ever go away on their own? 

Yes, especially if they’re related to an infection. Not so with any of the other possible causes, though. Cancer, in particular, will not go away on its own. 

Do lung nodules ever cause any symptoms?

Yes. Even if they’re benign, the nodules themselves or their underlying causes can cause some of the same symptoms as lung cancer, including: 

• A nagging cough 
• Shortness of breath 
• Chest pain or pressure 
• Persistent or recurrent upper respiratory infections 

How can you tell if a lung nodule is cancerous?

If a nodule appears completely calcified on imaging, as if the whole thing has turned to stone, it is not cancer. If it has some flecks of calcium in it, it might be cancerous. But if there’s no calcium in a nodule at all, we’re always going to find that suspicious. Still, there are three approaches to learning more.  

1. Watch it: Also known as surveillance, this means we monitor a nodule over time to see if it grows bigger, gets smaller or just stays the same. 
2. Re-image it: We use advanced imaging techniques — such as PET scans and high-resolution CT scans — to take a closer look. 
3. Sample it: We can either stick a needle in the nodule or remove the whole thing surgically. Either way, we’ll get a piece of it so we can biopsy the tissue. 

The only way to know for sure if something is cancer is to look at its cells under a microscope. But we have to balance the risk of biopsy with the risk of it being cancer. That’s why we usually take a wait-and-see approach if your risk is very low or there’s a clear reason for a nodule, such as a recent case of the flu.

On the other hand, if you have multiple nodules, smoke a pack a day and have a family history of lung cancer, we might go straight to biopsy, because all of those factors put you at higher risk of lung cancer. 

The longer a nodule remains unchanged, the lower your risk of cancer is and the more justified continued observation is, rather than exposing you to the risk of a biopsy. If a nodule remains stable and doesn’t grow over two years or more, it is not a cancer.  

How are lung nodules usually treated?

That depends on how many there are, what kind they are, and whether they are causing any problems. Even if a lung nodule is not cancerous, if it’s causing repeated infections or making breathing difficult, we’ll often remove it. 

But lung cancers and those that originate in other locations are treated very differently. So, there’s no one-size-fits-all answer.