Lung cancer is just one of many types of respiratory diseases. Some are contagious, and some aren’t. A group of bacteria called Mycobacterium avium complex (MAC) can cause a noncontagious lung infection known as pulmonary MAC disease, or MAC lung disease for short.

Having two lung diseases at the same time may leave you wondering if one caused the other. Although scientists haven’t established a cause and effect between MAC lung disease and lung cancer, the two diseases do share some similarities. Here’s what you should know.

What Are MAC Bacteria and MAC Lung Disease?

People are constantly exposed to MAC bacteria, which is naturally found in the environment. Activities like gardening can expose you to this bacteria, but fortunately, it’s usually harmless.

MAC exposure is most likely to affect people who:

• Are postmenopausal
• Are over age 65
• Have a history of smoking
• Have another lung disease, such as chronic obstructive pulmonary disease (COPD) or bronchiectasis

In addition, people with a weakened immune system, either from an autoimmune disorder or side effects of medical treatment — such as lung cancer treatment — have a higher risk of developing a MAC infection.

MAC Lung Disease

In the United States, MAC bacteria are responsible for about 80 percent of lung diseases. Over the past 20 years, this condition has been on the rise. Unlike contagious respiratory diseases, like tuberculosis, you can’t catch MAC lung disease from another person.

MAC lung disease is a serious condition that requires a lengthy course of antibiotics. Most people need to stay on antibiotics for 15 to 18 months — sometimes even longer. MAC lung disease can damage the lungs, so it’s important to get it treated as soon as possible.

Common MAC Lung Disease Symptoms

MAC lung disease causes many symptoms that may be confused with lung cancer and other lung diseases. Symptoms include a chronic (long-lasting) cough that can either produce mucus or be dry. It’s also possible to cough up blood with MAC lung disease and be short of breath.

Other symptoms that seem unrelated to the lungs can make it difficult to tell if you have MAC lung disease or another illness. Called nonspecific symptoms, these include:

• Low-grade fever
• Fatigue
• Night sweats
• Poor appetite

If your symptoms don’t go away after you’ve been treated for other lung diseases, it’s possible that you also have MAC lung disease.

Diagnosis of MAC Lung Disease

Your doctor can perform a few tests to figure out if you have MAC lung disease. They may start with a chest X-ray to look for lung abnormalities. Testing the excretions or sputum from your lungs over the course of several days will show if MAC bacteria are multiplying.

Since most people are exposed to MAC bacteria, testing positive once doesn’t necessarily mean you have an active infection. In some cases, your doctor may insert a small tube into your lungs to test and diagnose MAC lung disease. This procedure is called a bronchoscopy.

Potential Links Between MAC Lung Disease and Lung Cancer

Case reports have discussed some possible connections between MAC lung disease and lung cancer, but researchers haven’t yet shown a direct relationship between the two diseases. One study described three older people with lung cancer who received immune checkpoint inhibitors (ICIs, drugs that help the body recognize and attack cancer cells) and later developed MAC lung disease. The time between starting ICI treatment to being diagnosed with MAC disease was about 17 months.

A 2021 study in Japan focused on 79 people with cancer and pulmonary MAC disease, including 17 with lung cancer. The researchers noted that MAC disease was more commonly found in the same lobe (part) as the lung cancer in 9 of the 11 participants who hadn’t had lung cancer surgery. Most of the participants with lung cancer had adenocarcinoma (cancer of the cells that secrete mucus) and had stage 1 to 3 disease.

A retrospective study (research that looks back in time at a group of people) from South Korea examined the relationship between lung infections like MAC disease and lung cancer procedures. The researchers found that people who’d undergone lung cancer surgery had a 40 times higher chance of MAC disease than that of the general population.

Improvements in screening and the ability to diagnose lung cancer early have led to more people having lung cancer surgery sooner. However, infections are serious complications that can compromise quality of life and outcomes, so the impact of surgery on MAC infections is worth understanding better.

Shared Risk Factors

It’s still unclear how lung cancer or lung cancer treatments affect the development of MAC infections. The two diseases do share some risk factors. For example, older people are more likely to have MAC disease or lung cancer compared with younger people. Heavy alcohol consumption and exposure to smoke are also common risk factors, and certain environmental contributors affect who gets lung diseases like these.

When To Call Your Doctor

If you have lung cancer, it can be easy to assume that any lung symptoms are the result of your lung cancer. However, if your symptoms get worse while you’re being treated, tell your doctor. They can assess your symptoms and run tests to understand if you have another infection or condition like MAC lung disease.

It’s important to follow up with your oncology team about your concerns so they can ensure you’re getting the right treatment for all your medical conditions. Lung cancer treatment won’t cure MAC disease, and getting treated for MAC disease can help prevent further damage to your lungs.

Talk With Others Who Understand

MyLungCancerTeam is the social network for people with lung cancer and their loved ones. On MyLungCancerTeam, more than 13,000 members come together to ask questions, give advice, and share their experiences with others who understand life with lung cancer.

Have you developed other lung diseases or infections on top of lung cancer? How were you diagnosed and treated? Share your experiences in the comments below, or start a conversation by posting on MyLungCancerTeam.