Chemotherapy pneumonitis is a serious, but relatively uncommon, inflammatory reaction that occurs in the lungs of people undergoing certain cancer treatments. This adverse drug reaction involves the lung tissue itself and requires prompt medical attention to prevent severe complications. Unlike typical pneumonia, this condition is not caused by a bacterial or viral infection, but rather by the body’s reaction to the cancer medication. This inflammatory process can develop acutely or slowly, making awareness important for patients and caregivers.
What Chemotherapy Pneumonitis Is and Which Drugs Are Responsible
Pneumonitis is the inflammation of the lung tissue, specifically the interstitium and the alveoli, which are the tiny air sacs responsible for gas exchange. This condition is a form of interstitial lung disease (ILD). The chemotherapy drug causes direct injury to the lung cells or triggers an immune-mediated response, where the body’s immune system mistakenly attacks the lung tissue.
The mechanism of injury can vary by drug, ranging from oxidative stress and free radical damage to the activation of inflammatory cells like lymphocytes. Many different chemotherapy agents have been implicated in causing this toxicity, with risk varying significantly based on the specific drug, total dose, and individual patient factors. Classic agents with a high reported incidence include the antibiotic Bleomycin, the antimetabolite Methotrexate, and the alkylating agents Carmustine and Busulfan.
Newer classes of cancer treatments also carry a risk, such as certain targeted therapies like epidermal growth factor receptor (EGFR) inhibitors and mTOR inhibitors, including Everolimus. Immunotherapy agents, known as checkpoint inhibitors like Nivolumab and Pembrolizumab, can also trigger a form of immune-related pneumonitis. The risk increases when these agents are used in combination with each other or with prior radiation therapy to the chest.
How to Recognize the Symptoms
The most common signs of chemotherapy pneumonitis are non-specific and can easily be mistaken for other conditions, such as a cold or an infection. Patients typically experience increasing shortness of breath, medically known as dyspnea, which may worsen with activity.
A persistent, dry cough that does not produce mucus is another frequent symptom reported by patients. A low-grade fever, fatigue, and general malaise can also accompany the respiratory symptoms. The symptoms can be subtle and develop insidiously over several weeks or months.
The timing of onset is highly unpredictable. Symptoms may appear within days or weeks of starting a new regimen, or they can be significantly delayed, sometimes occurring months or even years after the chemotherapy treatment has been completed. Any new or worsening respiratory symptom should be reported immediately to the oncology team.
Confirming the Diagnosis: Testing Procedures
The process of confirming chemotherapy pneumonitis primarily involves ruling out other causes of lung inflammation, especially infection. The doctor will begin with a physical examination, listening to the lungs for abnormal sounds, such as fine crackles, which can indicate fluid or inflammation in the small airways. Initial imaging often includes a Chest X-ray, which may show hazy or diffuse changes in the lung fields. However, High-Resolution Computed Tomography (HRCT) of the chest is considered the gold standard imaging test.
An HRCT provides detailed cross-sectional images that can clearly visualize characteristic patterns of inflammation, such as ground-glass opacities. Blood tests are routinely performed to check for markers of inflammation and to help distinguish between drug-induced inflammation and an active infection. In some cases, a procedure called a bronchoscopy with bronchoalveolar lavage (BAL) may be necessary. During a BAL, fluid is collected for analysis to look for infectious organisms or specific inflammatory cells.
Treatment Strategies and Outlook
The first step in treating chemotherapy pneumonitis is the permanent discontinuation of the chemotherapy agent suspected of causing the reaction. Once the causative drug is stopped, the primary treatment strategy is the use of high-dose corticosteroids, such as prednisone or intravenous methylprednisolone. These potent anti-inflammatory medications are administered to rapidly suppress the immune response and reduce the inflammation in the lung tissue.
The typical initial course involves a high dose for one to two weeks, followed by a gradual tapering of the dose over several weeks to prevent a relapse. Supportive care measures are implemented concurrently, particularly oxygen therapy if the patient has low oxygen levels. In severe cases where the patient does not respond to corticosteroids, other immunosuppressive agents may be considered. Most individuals respond well to treatment, and the inflammation fully resolves, though recovery can be slow.
However, severe or untreated cases can lead to irreversible damage to the lungs, resulting in pulmonary fibrosis, which is the formation of scar tissue that stiffens the lungs. This scarring can permanently impair lung function and, in the most severe instances, can be fatal.