Melanoma is a cancer originating from melanocytes, the pigment-producing cells typically found in the skin, eyes, and mucous membranes. When melanoma cells detach from the primary tumor and travel to distant organs, the condition is classified as metastatic or Stage IV disease. The lungs are one of the most common sites for these secondary tumors to develop, making pulmonary involvement a frequent concern for individuals with advanced melanoma. While distant spread carries a serious outlook, modern therapies have significantly altered the trajectory of this disease.
Understanding Metastatic Spread to the Lungs
Melanoma cells achieve distant spread by entering the body’s circulatory systems, primarily traveling through the bloodstream in a process known as hematogenous dissemination. Once in circulation, these cells must survive the journey and evade immune surveillance before becoming lodged in the small blood vessels of a distant organ. The lungs are highly susceptible because all blood returning from the body must pass through the pulmonary capillaries for oxygenation, acting like a filter that traps circulating tumor cells.
After becoming trapped, the melanoma cells must adapt to the new microenvironment to establish a viable secondary tumor, known as a metastasis. This colonization process involves the cells manipulating their surroundings to promote tumor growth. The secondary tumors can vary widely, sometimes appearing as a single, isolated lesion, or more often as multiple nodules scattered throughout the lung tissue.
Recognizing Specific Lung Symptoms
The presence of melanoma metastases in the lungs does not always produce immediate or obvious symptoms, especially when the tumors are small. When symptoms manifest, they relate to the physical space the growing tumors occupy and the irritation they cause within the respiratory system. A frequently reported sign is a persistent cough that does not resolve, sometimes accompanied by bloody phlegm.
Shortness of breath (dyspnea) is a concerning symptom, which can occur as tumors restrict usable lung capacity or if fluid accumulates around the lungs (pleural effusion). Patients may also experience unexplained chest pain or discomfort. Beyond these respiratory signs, systemic symptoms like fatigue and a noticeable loss of appetite leading to weight loss are common indicators of advanced disease.
Diagnostic Procedures for Lung Metastases
Confirming the spread of melanoma to the lungs requires imaging technology and tissue analysis to locate the lesions and verify their cellular origin. Initial screening often involves a chest X-ray, but a computed tomography (CT) scan of the chest is the standard imaging method. CT scans provide detailed, cross-sectional images that clearly show the size and number of pulmonary nodules. Metastatic nodules typically appear as well-defined, round areas, often concentrated in the peripheral regions of the lungs.
To assess the full extent of the disease throughout the body, a positron emission tomography (PET) scan, frequently combined with a CT scan (PET/CT), is often employed. Melanoma cells exhibit high metabolic activity, causing them to intensely absorb the radioactive glucose tracer used in the PET scan, highlighting distant tumors. While imaging locates suspicious lesions, a tissue biopsy is necessary for definitive diagnosis and molecular analysis.
For centrally located lesions, a doctor may perform a bronchoscopy, passing a tube down the airway to take a sample. A CT-guided needle biopsy is used for tumors situated closer to the chest wall. This tissue sample is then analyzed to confirm the cells are melanoma and to identify specific genetic mutations, such as the BRAF V600 mutation, which directly informs treatment selection.
Current Treatment Approaches
The management of metastatic melanoma involving the lungs has been revolutionized by systemic therapies that specifically target the cancer’s biology. The choice of treatment is guided by the molecular profile of the tumor identified during the biopsy.
Targeted Therapy
For tumors with the common BRAF V600 mutation, targeted therapy is a first-line option. This utilizes a combination of BRAF inhibitors (like dabrafenib or vemurafenib) and MEK inhibitors (like trametinib or cobimetinib). This combination therapy blocks the specific signaling pathway that drives the rapid growth of the melanoma cells, often leading to a quick and significant tumor response.
Immunotherapy
For patients whose tumors do not have the BRAF mutation, or for those who stop responding to targeted therapy, immunotherapy is the standard approach. This therapy uses immune checkpoint inhibitors to release the natural brakes on the immune system’s T-cells. By freeing the T-cells, these drugs enable the body’s defenses to recognize and attack the cancer cells. Immune checkpoint inhibitors include:
- PD-1 blockers (like nivolumab or pembrolizumab)
- CTLA-4 blockers (like ipilimumab)
The combination of PD-1 and CTLA-4 inhibitors can offer superior effectiveness compared to using a single agent, though it also increases the risk of immune-related side effects.
Localized Treatments
In specific, carefully selected cases where the disease burden is limited to a few isolated lesions (oligometastasis), localized treatments may play a role. This can involve surgical removal of the tumor (pulmonary metastasectomy) or using focused radiation therapy to destroy the lesions. Surgical resection, when complete, can offer a significant survival benefit, with some studies showing a five-year survival rate of approximately 27% for highly selected patients.
Chemotherapy, while historically used, is now less frequently the primary treatment for metastatic melanoma. The overall outlook for metastatic melanoma has improved substantially with these modern agents, changing the standard of care from one focused on palliative measures to one where long-term survival is increasingly possible for a subset of patients. Participation in clinical trials is often encouraged, as researchers continue to investigate new combination strategies to overcome resistance and further improve outcomes.