What is the process of cancerous cells spreading to other body areas?
Metastasis: The Tumour's Invasion and Dispersal
Definition: Metastasis is a complex and multi-step biological process that characterizes the spread of cancer cells from their initial site of origin to distant locations in the body. This hallmark capability of metastasis is what sets malignant tumors apart from benign tumors and is responsible for the majority of cancer-related deaths.
Metastatic Cascade:
Local invasion: Cancer cells acquire the ability to break away from the primary tumor and invade the surrounding healthy tissues. This involves breaching the basement membrane—a thin layer of specialized proteins and collagen that separates the epithelial cells of the tissue from the underlying stroma.
Intravasation: Cancer cells enter the nearby bloodstream or lymphatic vessels. This process is known as intravasation. Through the bloodstream or the lymphatic system, these cancer cells can then spread to other parts of the body.
Circulating tumor cells (CTCs): Within the blood or lymphatic system, circulating tumor cells (CTCs) may form emboli or clusters. These emboli can get trapped in small blood or lymphatic vessels, ultimately leading to the next step in the metastatic cascade: extravasation.
Extravasation: In a similar fashion to intravasation, cancer cells must squeeze their way out of the blood or lymphatic vessels and penetrate the surrounding tissue to form secondary tumors. This step completes the metastatic cascade and ensures the establishment of distant metastases.
Microenvironment: The cells in the new microenvironment play a significant role in the successful establishment and growth of metastatic tumors. These cells can promote the survival, growth, invasion, and angiogenesis (development of new blood vessels) in metastasis, creating a conducive environment for tumor progression.
Dormancy: In some cases, tumor cells may undergo dormancy, remaining in a state of equilibrium at a distant site for a period of time before actively forming a secondary tumor. This phenomenon adds complexity to the metastatic cascade and understanding the mechanisms behind this latency can provide insights for improving cancer treatments.
Consequences of Metastasis:
Metastasis is a devastating process that accounts for over 90% of cancer-related deaths. Secondary tumors can affect vital organs, causing significant dysfunction, pain, and potential organ failure, ultimately leading to death in most cases.
Preventing and Treating Metastasis:
Preventing metastasis is a major focus of cancer research. If caught and treated before metastasis occurs, many cancers have high cure rates. Currently, most cancer therapies aim to eliminate the primary tumor and target metastatic foci to prevent further spread.
Understanding the mechanisms underlying metastasis is crucial for:
Developing effective therapies that prevent tumor cells from metastasizing.
Targeting and eradicating metastatic tumors that have already established.
Studying metastasis has also highlighted the importance of early detection and intervention to improve cancer outcomes and overall survival rates.