Cancer Metastasis: Step-by-Step How Cancer Spreads Through the Body

Metastasis—the spread of cancer from its primary site to distant organs—is a complex, multi-step process responsible for most cancer deaths. Understanding each step reveals targets for therapy.

The Metastatic Cascade

1. Local Invasion

Cancer cells breach the basement membrane and invade surrounding stroma. Enzymes (matrix metalloproteinases) degrade extracellular matrix. Cells acquire motility via epithelial-mesenchymal transition (EMT).

2. Intravasation

Cells enter blood vessels (hematogenous spread) or lymphatic vessels (lymphogenous spread). Lymphatic spread often reaches regional lymph nodes first.

3. Circulation & Survival

Circulating tumor cells (CTCs) face shear stress, immune attack (NK cells), and anoikis (detachment-induced death). Survivors often cluster with platelets for protection.

4. Extravasation

CTCs adhere to vessel endothelium (via selectins, integrins), transmigrate, and infiltrate the new tissue microenvironment.

5. Colonization & Outgrowth

The "seed and soil" hypothesis: only compatible organs (the "soil") support growth. Dormant cells may persist for years before reactivating. Angiogenesis and immune evasion are critical.

Common Metastatic Patterns

• Breast → bone, lung, liver, brain
• Lung → brain, bone, liver, adrenal glands
• Prostate → bone, lymph nodes
• Colorectal → liver, lung, peritoneum
• Melanoma → skin, lung, brain, liver, bone

Clinical Implications

• Staging (TNM) depends on metastatic spread.
• Liquid biopsies (CTC, ctDNA) detect metastasis early.
• Targeting EMT, angiogenesis, or organ-specific niches are active research areas.

Early detection and systemic therapies (chemotherapy, targeted therapy, immunotherapy) aim to interrupt this cascade.