Cancer metastasis

Cancer metastasis refers to the spread of cancer cells from the primary tumor site to distant parts of the body, forming new, secondary tumors. This process is a complex series of steps in which cancer cells leave the original tumor site, travel through the body via the bloodstream or lymphatic system, and establish new tumors in other organs or tissues. Metastasis is a hallmark of cancer malignancy, significantly complicating treatment and often worsening the prognosis.

Overview

The process of metastasis can be divided into several steps: local invasion, intravasation, transport, extravasation, and colonization. Initially, cancer cells invade the local tissue surrounding the primary tumor. Through intravasation, these cells then enter nearby blood or lymph vessels. While in circulation, they must survive the immune system's defenses and physical stresses. After circulating, cancer cells extravasate, exiting the vessels into the surrounding tissue of a distant site. Finally, they must adapt to and colonize this new environment to form a secondary tumor.

Mechanisms

The mechanisms underlying cancer metastasis involve changes in the cancer cells that allow them to become more mobile and invasive. This includes alterations in cell adhesion molecules, enabling detachment from the primary tumor and invasion into surrounding tissues. Cancer cells also undergo changes that allow them to survive and proliferate in a foreign microenvironment, a process known as the epithelial-mesenchymal transition (EMT).

Sites of Metastasis

Different cancers tend to metastasize to specific sites, a phenomenon known as organ tropism. For example, prostate cancer commonly spreads to the bones, while lung cancer prefers the brain and liver. The "seed and soil" theory suggests that certain cancer cells (the "seeds") have a predilection for the environment of specific organs (the "soil"), which are more conducive to their growth.

Diagnosis and Treatment

The diagnosis of metastatic cancer often involves imaging studies such as CT scans, MRI, and PET scans, as well as biopsy of the suspected metastatic lesions. Treatment typically focuses on systemic therapies such as chemotherapy, hormone therapy, targeted therapy, and immunotherapy, aiming to control or reduce the spread of cancer. In some cases, localized treatments like surgery or radiation therapy may be used to control symptoms or reduce tumor burden.

Prognosis

The prognosis for patients with metastatic cancer varies widely depending on the cancer type, the extent of spread, and the response to treatment. Generally, metastatic cancer is considered incurable, with treatments aimed at prolonging life and improving quality of life.

Prevention and Research

Efforts to prevent cancer metastasis are focused on understanding the molecular and cellular mechanisms that underlie the process. Research is ongoing into identifying biomarkers for early detection and targets for new therapies that could prevent or treat metastasis.