Breast cancer can cause breathing problems. These respiratory issues are not always a sign of cancer spreading but can arise from multiple distinct pathways. The difficulty in breathing, known medically as dyspnea, results from three main areas: the physical spread of cancer cells into the chest, side effects from necessary treatments, or broader systemic complications. Understanding these different causes is the first step toward effective diagnosis and management.
Direct Causes: Cancer Spread to the Lungs and Chest
When breast cancer cells travel through the bloodstream or lymphatic system, they can settle and grow in the lung tissue, a process called metastasis. These secondary tumors, or lesions, within the lung parenchyma compromise the organ’s ability to efficiently transfer oxygen into the blood. The presence of these lesions can cause symptoms like a persistent cough, wheezing, or shortness of breath, which may worsen as the tumor size or number increases.
Another common complication is the involvement of the pleura, the thin lining that surrounds the lungs and the inside of the chest wall. If cancer cells irritate this lining, it can lead to a build-up of fluid in the space between the lung and the chest wall, a condition known as malignant pleural effusion. This fluid compresses the lung, preventing it from fully expanding and causing significant breathlessness and sometimes chest pain, which is often worse when taking a deep breath.
Breast cancer cells may infiltrate and block the lymph channels within the lungs, a condition called lymphangitis carcinomatosa. This blockage prevents lymph fluid from draining properly, leading to inflammation and scarring that impairs the lung’s ability to oxygenate the blood. This type of involvement can cause profound breathlessness and a dry cough, sometimes even before the cancer is visible on standard chest imaging.
Indirect Causes: Treatment-Related Lung Toxicity
Many breast cancer therapies can inadvertently cause inflammation or scarring in the lungs, leading to breathing difficulties. Certain chemotherapy agents, such as taxanes (like paclitaxel and docetaxel), gemcitabine, and cyclophosphamide, are known to occasionally cause a side effect called chemotherapy-induced pneumonitis. This inflammatory reaction in the lung tissue presents with fever, dry cough, and shortness of breath, often occurring during or shortly after treatment.
Radiation therapy directed at the breast or chest wall can also damage lung tissue because the lung is often partially included in the treatment field. This can cause acute radiation pneumonitis, which typically develops one to three months after the completion of radiation and is characterized by inflammation, cough, and dyspnea. In some patients, this acute inflammation resolves but is followed by a late effect called radiation fibrosis, where the lung tissue scars and loses elasticity, which can cause long-term breathing issues.
Newer targeted therapies and immunotherapies also carry a risk of lung toxicity. Medications such as antibody-drug conjugates and immune checkpoint inhibitors can trigger an immune-related adverse event in the lungs, sometimes leading to pneumonitis. The mechanism involves the drug causing an unintended inflammatory response against the body’s own lung tissue.
Systemic Complications Affecting Respiration
Systemic problems related to cancer and its treatment can manifest as shortness of breath. Cancer patients have an increased risk of developing blood clots, a condition known as venous thromboembolism (VTE), which can be exacerbated by chemotherapy and limited mobility. If a blood clot travels from the legs or pelvis to the lungs, it causes a pulmonary embolism (PE). This serious condition blocks blood flow to a portion of the lung and causes sudden, sharp shortness of breath and chest pain.
Another cause of breathlessness is anemia, a reduction in red blood cells or the amount of hemoglobin they contain. Anemia is common in cancer patients due to the disease itself, chronic blood loss, or as a side effect of chemotherapy that suppresses bone marrow function. With fewer oxygen-carrying red blood cells, the body struggles to deliver adequate oxygen to tissues, leading to shortness of breath, particularly during physical exertion.
Cancer treatment, especially chemotherapy, often suppresses the immune system, leaving patients vulnerable to respiratory infections like bacterial or viral pneumonia. These infections cause inflammation and fluid accumulation in the air sacs of the lungs, impairing gas exchange. This results in a productive cough, fever, and breathing difficulty. Prompt identification and treatment of these infections are necessary to prevent respiratory failure.
Identifying and Treating Respiratory Distress
Recognizing the signs of respiratory distress is important for anyone undergoing breast cancer treatment. Patients should seek medical attention promptly for symptoms such as a new or persistent cough, sudden or worsening shortness of breath, pain when breathing, or wheezing. These symptoms, especially if accompanied by fever or coughing up blood, require immediate medical evaluation to determine the underlying cause.
Diagnosis begins with a physical examination and medical history, focusing on recent treatments, followed by imaging studies. A chest X-ray or a computed tomography (CT) scan is typically used to visualize the lungs, looking for tumor lesions, signs of inflammation, or fluid accumulation (pleural effusion). If a pulmonary embolism is suspected, a CT pulmonary angiography or a ventilation-perfusion (V/Q) scan may be performed to check for blockages in the lung arteries.
Treatment is specific to the identified cause of the respiratory problem. For malignant pleural effusion, the fluid can be drained using a needle in a procedure called thoracentesis, which immediately relieves pressure on the lung. If the cause is pneumonitis from chemotherapy or radiation, corticosteroids (such as prednisone) are the standard treatment to reduce inflammation in the lungs. When a pulmonary embolism is diagnosed, the patient is treated with blood thinners (anticoagulants) to prevent the clot from growing and allow the body to dissolve it. In cases of severe anemia, a blood transfusion can quickly restore the oxygen-carrying capacity of the blood and alleviate shortness of breath.