When cancer cells from a tumor in the colon or rectum travel to the lungs and form new tumors, it is known as colon cancer metastasis to the lung. This development represents an advanced stage of the disease and is still classified as colon cancer, not primary lung cancer. The cancerous cells in the lungs retain the characteristics of the original colon tumor. Therefore, treatments are designed to target the biological makeup of colon cancer cells, which is a foundational concept for diagnosis and therapy.
How Colon Cancer Spreads to the Lungs
The process by which colon cancer spreads is called metastasis. It begins when cancer cells break away from the original tumor in the colon and enter the bloodstream or the lymphatic system.
Once in circulation, the cancer cells travel until they become lodged in small blood vessels, or capillaries, in a distant organ. Blood from the intestinal walls first passes through the liver and then returns to the heart, which pumps it directly to the lungs. This circulatory route makes the lungs one of the first capillary beds that stray colon cancer cells encounter. The dense network of small vessels in the lungs can trap these traveling cells.
If the trapped cells adapt to the new environment, they can multiply and form new tumors. This requires creating their own blood supply, a process called angiogenesis, to receive nutrients for growth. The specific molecular properties of certain colon cancer cells may make them more adept at surviving this journey and thriving in lung tissue.
Symptoms and Diagnosis of Lung Metastases
The spread of colon cancer to the lungs may not produce noticeable symptoms at first. Metastases are often discovered during routine follow-up imaging for the primary colon cancer, which is a standard part of post-treatment surveillance.
When symptoms do appear, they can be subtle. Potential indicators include:
- A persistent cough that does not resolve
- Shortness of breath
- Chest discomfort or pain
- Wheezing
- Coughing up blood
General fatigue and unexplained weight loss can also accompany the spread of cancer.
Imaging studies are the primary tool for detecting nodules in the lungs. A computed tomography (CT) scan of the chest provides detailed cross-sectional images. A positron emission tomography (PET) scan, which detects areas of high metabolic activity, may also be used, often in combination with a CT scan (PET-CT).
If imaging scans reveal suspicious nodules, a biopsy is performed to confirm the diagnosis. This involves taking a small tissue sample from the lung nodule for examination. A biopsy can be done with a needle guided through the chest wall or a bronchoscopy, where a flexible tube is passed into the airways. The examination verifies that the cells are cancerous and originated from the colon.
Blood tests for tumor markers, such as carcinoembryonic antigen (CEA), are also part of the diagnostic and monitoring process. While not used for the initial diagnosis of lung metastases, a significant rise in CEA levels in a patient with a history of colon cancer can prompt further investigation with imaging.
Treatment for Colon Cancer in the Lungs
Treatment for colon cancer that has spread to the lungs is individualized, depending on the number and location of tumors, the patient’s health, and the cancer’s molecular characteristics. A combination of systemic and local therapies is often employed, with systemic treatments circulating throughout the body to target cancer cells.
Systemic therapies form the basis of treatment for many patients. Chemotherapy uses drugs to kill cancer cells, while targeted therapy uses drugs that attack specific aspects of cancer cells. Before starting targeted therapy, biomarker testing looks for genetic mutations like KRAS, NRAS, and BRAF to determine which drugs are most effective. Immunotherapy, which helps the body’s immune system fight cancer, is an option for tumors with high microsatellite instability (MSI-H) or mismatch repair deficiency (dMMR).
Alongside systemic treatments, local therapies focus directly on the tumors in the lungs. Surgery to remove the lung metastases, known as a metastasectomy, may be an option if there are a limited number of tumors in safe locations. For patients who are not candidates for surgery, other local therapies are available, such as Stereotactic Body Radiation Therapy (SBRT) or ablation techniques like radiofrequency ablation (RFA), which uses heat to destroy cancer cells.
Oligometastatic disease is a state where a person has a small number of metastatic tumors, such as five or fewer nodules in the lungs. Patients with this condition may be candidates for more aggressive local treatments like surgery or SBRT. These treatments can sometimes achieve long-term disease control or a cure, and the decision to pursue them is made by a multidisciplinary team of specialists.
Outlook and Follow-Up Care
The outlook for individuals with colon cancer that has spread to the lungs varies. The number of metastases, the person’s overall health, and how the cancer responds to treatment all influence the prognosis. While metastases indicate an advanced stage of cancer, outcomes have improved with modern treatments.
Follow-up care is a continuous part of managing the disease and involves regular visits with an oncologist. A component of follow-up is scheduled imaging, such as CT or PET scans, to monitor for any cancer recurrence or progression. Blood tests to monitor tumor markers like CEA are also standard, as changes in these levels can provide an early indication of changes in disease activity. This regular monitoring allows the healthcare team to adjust the treatment plan if needed.
Palliative care, which focuses on providing relief from the symptoms and stress of a serious illness, may be integrated into the care plan at any stage. The goal is to improve the quality of life for both the patient and their family. It can help manage symptoms like pain or shortness of breath and provide emotional and psychological support.