Invasion and metastasis of neoplasms

1. Invasion

	Invasion	Metastasis
Benign	Expansive (capsule)	No
Malignant	Infiltrative (no capsule)	Yes
Semi-malignant	Expansive, encapsulated	No
Borderline (CIS)	Localized, BM preserved	No

• Benign — expansive growth → atrophy of surrounding tissue → fibrous capsule (easily removed); not all are encapsulated (uterine leiomyoma).
• Malignant — infiltrative, destructive, non-cohesive, no capsule; local invasiveness = malignancy.
• Carcinoma in situ (borderline) — does not penetrate the basement membrane → no access to vessels/lymph → no metastasis.

2. Metastasis

Breaking away from the primary to form distant tumors. Metastasis = definitive sign of malignancy; more likely with larger, more anaplastic primaries.

Routes

Route	Typical of	Examples
Lymphatic	Carcinomas (most common)	Breast → axillary nodes; lung → bronchial/hilar nodes
Hematogenous	Sarcomas (via veins)	Intestine → portal → liver; caval → lung; thyroid/prostate → vertebrae (paravertebral plexus)
Transcoelomic (seeding)	Body cavities	Ovarian → peritoneum; lung → pleura; CNS → CSF

• Sentinel lymph node — first node draining a tumor (blue dye/radiotracer biopsy).
• Skip metastases — alternative channels bypass the next node.
• Veins are invaded more than arteries (renal cell carcinoma → renal vein; HCC → hepatic/portal vein).

3. Metastatic cascade

1. Detachment — loss of E-cadherin (also removes anti-growth signal).
2. ECM/BM degradation — matrix metalloproteinases (collagenase, gelatinase).
3. Migration — attachment to ECM (fibronectin) + autocrine motility factor; matrix remodeling.
4. Vascular dissemination → arrest at distant site → extravasation → colonization (“seed and soil” organ tropism); EMT underlies the phenotype.

💡 High-yield: CIS = malignant cytology, BM intact, no metastasis. Cascade: ↓ E-cadherin → MMP degradation → migration → vascular spread (EMT). Routes: carcinoma = lymphatic, sarcoma = hematogenous, ovarian = transcoelomic. Sentinel node = first draining node; “seed and soil” tropism.