A lung mass is a growth in the lung that measures more than 3 centimeters (about 1.25 inches) across. Anything smaller than that threshold is called a lung nodule. The distinction matters because larger growths carry a higher probability of being cancerous, which changes how quickly doctors pursue testing. That said, not every lung mass is cancer. Infections, benign tumors, and inflammatory conditions can all produce growths that cross the 3-centimeter line.
How a Mass Differs From a Nodule
The 3-centimeter cutoff is the dividing line radiologists use when reading a CT scan. Below that size, a growth is a pulmonary nodule. Above it, it’s classified as a mass. This isn’t just a naming convention. Size is one of the strongest predictors of malignancy. Nodules smaller than 5 millimeters have a cancer probability of roughly 0.4%, which is essentially the same risk as having no nodule at all. Nodules between 5 and 10 millimeters carry about a 1.3% cancer probability. Once a growth reaches 10 millimeters or larger, the probability jumps to around 15%, and it continues to climb with size. By the time a growth qualifies as a mass, the chance of malignancy is significant enough that doctors typically move straight to a diagnostic workup rather than a wait-and-watch approach.
What Causes a Lung Mass
Lung cancer is the most concerning possibility, but several non-cancerous conditions produce masses as well. Understanding the range of causes can help put the finding in context.
Benign Causes
Hamartomas are the most common benign lung tumors. They’re made up of normal tissues like cartilage, fat, and connective tissue, just arranged in abnormal amounts. They tend to stay contained and rarely press on surrounding structures. Bronchial adenomas grow in the airways and mucus gland ducts. Papillomas are less common and grow as projections inside the bronchial tubes. Infections, particularly fungal infections and tuberculosis, can also leave behind granulomas (clumps of inflammatory tissue) large enough to be classified as masses. Sarcoidosis, an inflammatory disease that causes clusters of immune cells in the lungs, is another possibility.
Malignant Causes
Lung cancer is the primary concern when a mass is found, especially in people with risk factors. Smoking remains the leading cause, but it’s far from the only one. Occupational exposure to asbestos, arsenic, beryllium, cadmium, chromium, and silica dust all raise the risk. Radon gas, which seeps into homes from underground, is the second leading cause of lung cancer after smoking. Indoor and outdoor air pollution also contribute. A mass can also represent cancer that started somewhere else in the body and spread to the lungs, known as a metastatic lesion.
What Doctors Look for on Imaging
When a lung mass shows up on a CT scan, radiologists examine several features to gauge how suspicious it looks. The edges of the growth are particularly telling. Smooth, well-defined borders are more common in benign growths. Spiculated margins, where the edges look jagged or spiky with projections radiating outward, are a hallmark of malignancy. Location matters too. Masses in the upper lobes of the lungs carry a higher cancer risk statistically.
Calcification patterns within the mass also provide clues. Certain patterns of calcium deposits, like a central or “popcorn” pattern, suggest benign causes such as old infections or hamartomas. Irregular or absent calcification is more worrisome. Doctors also factor in the patient’s age, smoking history, and whether the mass has grown compared to any prior imaging.
PET Scans and Activity Levels
If a CT scan raises concern, doctors often order a PET scan. This test works by injecting a small amount of radioactive sugar into your bloodstream. Cancer cells are metabolically active and absorb more sugar than normal cells, so they light up on the scan. The intensity of that uptake is measured as a standardized uptake value, or SUV.
An SUV of 2.5 is the most widely used threshold for flagging a mass as suspicious. At that cutoff, PET scans correctly identify about 89% of cancerous growths and correctly clear about 84% of benign ones. Some research suggests that raising the threshold to 4.0 or 4.5 improves overall accuracy, but the lower cutoff catches more true cancers at the cost of some false alarms. A PET scan isn’t definitive on its own. Some infections and inflammatory conditions also produce high uptake, and some slow-growing cancers may not light up at all.
How a Biopsy Is Done
When imaging can’t rule out cancer, a tissue sample is needed. There are two main approaches, and the choice depends largely on where the mass sits in the lung.
A transthoracic needle biopsy involves passing a needle through the chest wall, guided by real-time CT images. It’s highly accurate, providing a diagnosis in up to 90% of cases. The main drawback is the risk of pneumothorax, a partial lung collapse caused by the needle puncturing the lung lining, which happens in up to 25% of procedures. Most cases are minor and resolve on their own, though some require a small chest tube.
Navigational bronchoscopy takes a different route. A thin, flexible catheter is guided through your airways to reach the mass, using a GPS-like system mapped from your CT scan. Because the approach stays inside the airways and doesn’t pierce the lung lining, the pneumothorax rate drops to about 2%. This method works best for masses that are accessible through the airway tree. For masses sitting at the edge of the lung, a needle biopsy may be the better option.
Risk Factors That Raise Concern
Doctors assess your overall risk profile alongside the imaging findings. The factors that push a lung mass higher on the suspicion scale include older age, a heavy smoking history (current or past), upper lobe location of the mass, and spiculated or irregular margins. If your annual risk of developing lung cancer exceeds about 5%, guidelines classify you as high risk, which changes how aggressively the mass is investigated and how quickly.
People with no smoking history and no occupational exposures can still develop lung masses, both benign and malignant. But the statistical probability of cancer is substantially lower in this group, which may allow for a more measured diagnostic timeline in borderline cases.
What Happens if Surgery Is Needed
If a mass is confirmed as cancerous, or if it’s large and suspicious enough to warrant removal without a definitive biopsy, surgery is often the next step. One of the least invasive options is a wedge resection, which removes a small, wedge-shaped section of lung tissue containing the mass along with a margin of healthy tissue around it.
This can be done two ways. An open thoracotomy, the traditional approach, involves a larger incision and typically requires five to seven days in the hospital. A video-assisted thoracoscopic surgery (VATS) approach uses small incisions and a camera, often allowing you to go home after just one night. After recovery, most people with otherwise healthy lungs return to normal activities, even with that small portion of tissue removed. For larger or more centrally located masses, more extensive surgery such as removing an entire lobe of the lung may be necessary.
Follow-Up for Uncertain Findings
Not every lung mass goes straight to biopsy. When the features are ambiguous, doctors may recommend a follow-up CT scan in a few weeks or months to check whether the mass is growing. The speed of growth, measured as the volume-doubling time, helps stratify risk. Masses that double in volume in under 400 days carry a cancer probability of about 10%. Those that take longer than 600 days to double have a probability closer to 1%. Very slow growth or no growth at all over multiple scans is reassuring, though it doesn’t completely eliminate the possibility of a slow-growing cancer.
The Fleischner Society guidelines, last updated in 2017, provide the framework most radiologists and pulmonologists follow for deciding when to scan again, when to biopsy, and when to simply monitor. These recommendations are tailored to each patient’s individual risk level and the specific characteristics of the mass on imaging.