Radiation therapy — which destroys cancer cells — can effectively treat breast cancer after a lumpectomy or mastectomy. However, it comes with potential risks to your heart and lung health. Understanding these risks can help you recognize symptoms and get the care you need.

If you’ve had breast cancer radiation therapy — also known as radiotherapy — your doctor will monitor you for side effects in your chest wall with follow-up examinations. Always discuss any chest symptoms with your oncologist and health care team. Importantly, smoking increases your risk of heart and lung problems considerably, so your care team likely will advise you to avoid smoking or join a cessation program.

Some types of heart and lung effects, known as short-term complications, can occur within weeks or months of radiation treatment. Long-term complications can take as long as 20 years to develop.

The following heart and lung conditions may occur from breast cancer radiation.

1. Pneumonitis

Pneumonitis is inflammation or irritation of the lung that is not infectious. A 2023 study found that 38 percent of people who received radiation therapy for breast cancer developed pneumonitis. Of those radiation-induced pneumonitis cases, 10 percent were symptomatic.

The risk of pneumonitis increases with higher doses of radiation. Smoking, age, and treatment in combination with the drugs goserelin (Zoladex) and tamoxifen are also risk factors. Pneumonitis usually develops short term within a few months of radiation therapy but may occur years after treatment. It can potentially lead to pulmonary (lung fibrosis) — scarring and hardening of connective tissue in the lungs.

Symptoms of pneumonitis include:

• Cough
• Shortness of breath
• Fatigue
• Loss of appetite

Treatment options include oral corticosteroids and oxygen therapy.

2. Worsening Asthma Symptoms

If you have asthma or other types of chest problems, your symptoms may worsen due to pneumonitis. Always discuss any preexisting lung conditions with your radiation oncologist and health care providers if you’re planning to have radiation treatment.

3. Lung Fibrosis

About 10 percent to 15 percent of people who have radiation for breast cancer develop radiation-induced lung fibrosis. Symptoms include dry cough and shortness of breath. Lung fibrosis progresses over time, although many people live actively with the condition. Treatment options include medication that slows scarring and oxygen therapy.

4. Lung Cancer

Undergoing radiation treatment for breast cancer may increase your overall risk for lung cancer by almost 60 percent, according to a large-scale 2021 study. The overall cumulative incidence of lung cancer was still low — researchers found that over 20 years, 3 percent of women with breast cancer who’d received radiation therapy went on to develop lung cancer compared to 2.3 percent of those who didn’t receive radiation treatment.

The risk of lung cancer increases in the years following radiation therapy, and it’s higher among people who smoke. Lower doses of radiation and breathing-adaptation exercises may help reduce the risk. Talk to your doctor about whether you may be at risk.

5. Radiation Heart Disease

Radiation therapy may cause a number of different heart conditions. Higher amounts of radiation can further increase those risks. The risk is also higher when radiation treatment is left-sided, which is nearer to the heart.

In one study of women aged 55 and under living with breast cancer, 10.5 percent of those who received left-sided radiation treatment developed coronary artery disease (CAD), the most common form of heart disease in the U.S. By comparison, only 5.8 percent of those who received right-sided radiation therapy developed CAD. Notably, that 5.8 percent is in line with the prevalence of CAD among women 20 and over in the U.S., according to the Centers for Disease Control and Prevention.

Short-Term Heart Complications

People who’ve undergone radiation therapy have a higher risk of developing short-term pericarditis — inflammation of the pericardium (sac) that surrounds the heart. Symptoms include:

• Chest pain
• Pain in the left shoulder, back, or neck
• Difficulty breathing
• Heart palpitations (rapid beating)

Pericarditis is often treated with rest and nonsteroidal anti-inflammatory drugs (NSAIDs) or other anti-inflammatory medication. Most people make a full recovery.

In pericardial effusion, fluid collects in the pericardium, which can cause heart damage and be life-threatening. Symptoms include:

• Chest pain
• Shortness of breath
• Heart palpitations
• Light-headedness or fainting

The condition can be treated with anti-inflammatory medication or, in more serious cases, by draining fluid with a needle or surgery.

Long-Term Complications

Some types of radiation-induced heart disease can develop over years and may be serious, including:

• Congestive heart failure
• Cardiomyopathy (enlarged heart)
• Coronary artery disease
• Arrhythmia (irregular heartbeat)
• Valvular heart disease
• Constrictive pericarditis (thickening of the pericardium)

Factors that increase your risk for heart complications following radiation therapy include:

• History of heart disease
• High cholesterol
• Diabetes
• Combined treatment with chemotherapy drugs that have a risk of cardiotoxicity (heart-damaging properties)

Smoking, excessive alcohol consumption, and high body weight are all highly detrimental to heart health.

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