Spread and metastasis of lung cancer

The growth rate, spread and metastasis of lung cancer depend on the histological type and degree of differentiation of cancer cells and the immune function status of the patient. Generally, there are several pathways as follows.

1. Local direct spread

After the cancer occurs in the bronchial wall, it can grow into the bronchial cavity, causing the cavity to narrow or completely block. When the cancer grows outside the bronchus, it invades the lung tissue, and then spreads to invade the adjacent organs and tissues. After the central lung cancer spreads to the hilum and mediastinum, it can compress or invade the lymph, blood vessels, nerves, and various organs and tissues located in the mediastinum. Peripheral lung cancer near the edge of the lung often invades the pleura, causing pleural effusion and chest wall metastasis. The cancer can also penetrate the interlobar fissures and invade other adjacent lobes. Huge tumors form cancerous cavities due to ischemia, tissue necrosis, and liquefaction in the central part.

2. Lymphatic metastasis

Lymphatic metastasis is a common and main route of spread of bronchogenic lung cancer. Well-differentiated small cell carcinoma can metastasize via the lymph nodes at an early stage, and squamous cell carcinoma metastasizes via the lymph nodes very frequently. Adenocarcinoma often metastasizes via the blood vessels, but lymphatic metastasis can also occur. Cancer cells first invade the adjacent lung segments or lobes, parabronchial lymph nodes through the lymphatic vessels around the bronchi and pulmonary blood vessels, and then reach the hilar, subtracheal carina, mediastinal, paratracheal lymph nodes according to the location of the lung cancer, and then involve the supraclavicular, anterior scalene muscles, and cervical lymph nodes. Mediastinal paratracheal and cervical lymph node metastasis generally occurs on the same side of the lung cancer, while lymphatic metastasis of left-sided lung cancer can occur on the opposite side of the lung cancer, which is the so-called cross-metastasis. After lung cancer invades the chest wall and diaphragmatic pleura, it can metastasize to the axillary, cervical, and upper abdominal lymph nodes via the lymphatic channels.

3. Hematogenous metastasis

Lung cancer with hematogenous metastasis has entered the late stage. Undifferentiated cancer can metastasize to the bloodstream earlier, and adenocarcinoma metastasizes more often through the bloodstream. Advanced squamous cell carcinoma metastasizes through the bloodstream as well. Cancer cells usually invade the pulmonary venous system and then metastasize to organs and tissues throughout the body through the left heart with the systemic blood flow. The most common sites of metastasis are the liver, bones, adrenal glands, kidneys, brain, etc.

4. Airway spread

In a few cases of lung cancer, cancer cells that have shed can spread through the trachea and implant into other lung segments or lobes on the same or opposite side, forming new cancer foci. Bronchioloalveolar carcinoma is more likely to spread through the airways.