Metastasis — Routes & Patterns
Pathology · Neoplasia · lean revision notes
Metastasis — Routes & Patterns
Metastasis is the spread of malignant cells from a primary tumour to a non-contiguous distant site where they establish a secondary growth. It is the single most reliable evidence of malignancy and the dominant cause of cancer death. This topic is a perennial NEET PG favourite for its crisp one-liners — Virchow node, Krukenberg tumour, Sister Mary Joseph nodule, and the lytic-vs-sclerotic bone metastasis distinction.
High-yield: The presence of metastasis = definitive proof of malignancy. The two features that unequivocally distinguish a malignant from a benign tumour are metastasis and invasion — of the two, metastasis is the more reliable single criterion (invasion can occasionally be mimicked).
Definition & basic concepts
- Primary tumour — the site of origin.
- Secondary / metastatic deposit — the colony at the distant site; histologically resembles the primary, not the host organ.
- Roughly 30% of patients with newly diagnosed solid tumours already have clinically detectable metastases; many more harbour micrometastases.
- Benign tumours and most tumours of the CNS (gliomas) and skin (basal cell carcinoma) essentially do not metastasise despite local aggressiveness — a classic exam exception.
High-yield: Gliomas (e.g. glioblastoma) and basal cell carcinoma are highly invasive but rarely metastasise. Conversely, even tiny primaries (e.g. occult papillary thyroid carcinoma, choriocarcinoma) can metastasise widely.
The metastatic cascade (pathophysiology)
Metastasis is a stepwise, grossly inefficient process — fewer than 0.01% of cells entering circulation form metastases. The sequence:
Invasion of basement membrane → detachment & loosening → degradation of ECM → migration → intravasation → survival in circulation (as tumour emboli, often platelet-coated) → arrest & extravasation → micrometastasis → angiogenesis & colonisation (overt metastasis)
Key molecular players (frequently asked):
| Step | Key molecule / event |
|---|---|
| Loosening of cell-cell contacts | Loss/down-regulation of E-cadherin |
| ECM degradation | MMPs (matrix metalloproteinases), cathepsin D, urokinase plasminogen activator |
| Attachment to ECM | Laminin receptor, integrins |
| Migration | Autocrine motility factor, cleavage products of collagen/laminin |
| Vascular dissemination | Tumour cells aggregate with platelets (homotypic + heterotypic adhesion) for protection |
| Colonisation | Angiogenesis via VEGF, escape from immunity |
High-yield: Loss of E-cadherin is the central early event permitting detachment and is the hallmark of epithelial-to-mesenchymal transition (EMT). E-cadherin loss is characteristic of lobular carcinoma of breast and diffuse (signet-ring) gastric carcinoma — both then favour transcoelomic/peritoneal spread.
Seed and soil hypothesis (Stephen Paget, 1889): Metastatic colonisation depends not only on cells reaching a site (the "seed") but on a compatible microenvironment (the "soil"). This explains organ tropism that cannot be predicted by blood flow alone (e.g. prostate → bone).
Routes of metastasis
There are four classic routes. Carcinomas typically prefer lymphatics first; sarcomas typically prefer the bloodstream — though overlap is large.
| Route | Typical tumours | Classic destinations |
|---|---|---|
| Lymphatic | Carcinomas (most) | Regional draining nodes → Virchow node |
| Haematogenous | Sarcomas; also RCC, HCC, follicular thyroid, choriocarcinoma | Liver, lung, bone, brain |
| Transcoelomic (seeding of body cavities) | Ovary, stomach, colon, pancreas; mesothelioma; lung | Peritoneum (Krukenberg, omental cake), pleura, pericardium |
| Implantation / iatrogenic | Surgical/needle-track seeding | Scar, biopsy track, surgical field |
1. Lymphatic spread
- Predominant route for carcinomas.
- Follows natural lymphatic drainage → the first regional node is reached initially (basis of the sentinel lymph node biopsy, especially in breast cancer and melanoma).
- Skip metastasis — nodes may be bypassed due to venous-lymphatic anastomoses or obstructed channels.
- Sentinel node identified using blue dye (isosulfan/patent blue) + radiolabelled colloid (technetium-99m sulfur colloid).
Named lymph node metastases (exam gold):
| Eponym / node | Significance |
|---|---|
| Virchow node (left supraclavicular, Troisier sign) | Classically gastric carcinoma; also other GI/abdominal malignancies via thoracic duct |
| Sister Mary Joseph nodule | Periumbilical metastatic nodule; GI (stomach) and ovarian primaries |
| Irish node | Left axillary node from gastric carcinoma |
| Krukenberg tumour | Bilateral ovarian metastasis (signet-ring) — usually transcoelomic/lymphatic from stomach |
High-yield: Virchow node = left supraclavicular node; palpable enlargement = Troisier sign. Classic primary = carcinoma stomach. It drains via the thoracic duct which empties near the left subclavian–internal jugular junction.
2. Haematogenous spread
- Predominant route for sarcomas; also for certain epithelial cancers with a propensity for vascular invasion.
- Veins (thin-walled) are invaded more often than arteries.
- Two anatomical drainage patterns determine first capillary bed reached:
- Portal drainage (GI tract organs: stomach, colon, pancreas) → liver first.
- Caval drainage (most other sites) → lung first.
High-yield: Liver and lung are the two most common sites of haematogenous metastasis overall, because they are the first capillary beds encountered by portal and caval venous return respectively.
Cancers notorious for early/predominant haematogenous spread (mnemonic "RCC FoCH"):
- Renal cell carcinoma (cannonball lung mets, IVC tumour thrombus)
- Choriocarcinoma
- Cell carcinoma — follicular thyroid (vs papillary which is lymphatic)
- Hepatocellular carcinoma
- (also testicular, osteosarcoma)
High-yield: Follicular thyroid carcinoma → haematogenous (bone, lung). Papillary thyroid carcinoma → lymphatic (cervical nodes). This contrast is asked repeatedly.
Batson's vertebral venous plexus — a valveless network of veins connecting pelvic/thoracic viscera to the vertebral column and brain, allowing prostate and breast cancer to seed the vertebrae and pelvis without first passing through the lungs.
High-yield: Batson plexus explains why prostate carcinoma preferentially metastasises to the lumbar spine and pelvis (osteoblastic lesions), bypassing the pulmonary filter.
3. Transcoelomic (serosal seeding) spread
- Tumour cells penetrate a serosal surface and seed a body cavity.
- Most common cavity = peritoneum; also pleura and pericardium.
- Produces malignant effusions and serosal studding.
Classic manifestations:
- Krukenberg tumour — bilateral ovarian deposits of signet-ring mucin-secreting cells, classically from gastric (diffuse/linitis plastica) carcinoma; less often colon/breast.
- Omental caking — diffuse omental tumour (ovarian carcinoma).
- Pseudomyxoma peritonei — gelatinous mucinous peritoneal disease from appendiceal (or ovarian mucinous) tumours.
- Blumer shelf — palpable rectal-shelf deposit in the pouch of Douglas on PR examination.
High-yield: Krukenberg tumour = bilateral ovarian metastasis with signet-ring cells in a mucin-rich, cellular stroma; commonest primary = stomach (then colon, breast). Spread is typically transcoelomic ± lymphatic/retrograde.
4. Implantation / iatrogenic spread
- Mechanical transfer of cells along instruments, needle tracks, or surgical fields.
- Examples: needle-track seeding after biopsy of HCC or mesothelioma; port-site recurrence after laparoscopy; surgical wound implantation.
- Rare but exam-worthy as the "fourth route."
Organ-specific metastatic patterns
Beyond simple anatomy, organ tropism (seed & soil) governs preferred sites.
| Common metastatic site | Most frequent primaries |
|---|---|
| Liver | GI tract (colorectal), pancreas, lung, breast |
| Lung | Breast, colorectal, kidney (RCC), head & neck, sarcomas, choriocarcinoma |
| Bone | Breast, prostate, lung, kidney, thyroid |
| Brain | Lung, breast, melanoma, kidney, colorectal |
| Adrenal | Lung, breast |
Mnemonic for cancers that commonly metastasise to bone — "BLT with a Kosher Pickle": Breast, Lung, Thyroid, Kidney, Prostate.
High-yield: Lung carcinoma is the single most common source of brain metastases. Most metastatic brain deposits lie at the grey–white junction and are multiple and well-circumscribed — a useful imaging clue versus primary gliomas.
Bone metastasis — lytic vs sclerotic (osteoblastic)
This is one of the most asked single facts in the chapter.
| Feature | Osteolytic (bone destruction) | Osteoblastic / sclerotic (bone formation) |
|---|---|---|
| X-ray | Radiolucent, "punched-out" | Radiodense, sclerotic |
| Classic primaries | Kidney (RCC), thyroid, lung, GIT, multiple myeloma, melanoma | Prostate (most classic), breast (mixed) |
| Calcium | Hypercalcaemia common | Usually normal/low |
| Alk phos | Variable | Often raised |
High-yield: Prostate carcinoma → osteoblastic (sclerotic) bone metastasis. Most other carcinomas (RCC, thyroid, lung) and multiple myeloma → osteolytic lesions. Breast cancer is typically mixed.
High-yield: Multiple myeloma produces lytic lesions but the bone scan is often "cold"/falsely negative because there is little osteoblastic reaction — use a skeletal survey / MRI, not a Tc-99m bone scan. In most other lytic/blastic mets, the bone scan is the screening test of choice.
- Most common overall site of skeletal metastasis = vertebral column (axial, red-marrow-rich skeleton via Batson plexus).
- Bone metastases are far more common than primary bone tumours.
Clinical features
Metastatic disease may be the presenting feature (cancer of unknown primary, CUP):
- Liver mets — hepatomegaly, nodular liver, deranged LFTs (raised ALP/GGT), jaundice late.
- Lung mets — often asymptomatic; "cannonball" nodules (RCC, choriocarcinoma, sarcoma); lymphangitis carcinomatosa causes dyspnoea.
- Bone mets — bone pain, pathological fracture, hypercalcaemia, spinal cord compression, marrow infiltration (leucoerythroblastic anaemia).
- Brain mets — headache, seizures, focal deficits, raised ICP.
- Peritoneal — ascites, bowel obstruction, palpable masses, Sister Mary Joseph nodule.
High-yield: A leucoerythroblastic blood picture (nucleated RBCs + immature myeloid cells in peripheral blood) suggests marrow infiltration by metastases (commonly breast, prostate).
Diagnosis & investigation of choice
A stepwise approach to suspected metastatic disease / cancer of unknown primary:
- History & examination including nodal survey, breast, prostate (PR), pelvis.
- Imaging — contrast CT chest/abdomen/pelvis for staging; MRI for brain/spine; bone scan (Tc-99m MDP) for skeletal screening.
- Whole-body FDG-PET/CT — best single modality to locate an occult primary and assess distant disease.
- Tissue diagnosis — biopsy of the most accessible deposit; histology resembles the primary.
- Immunohistochemistry (IHC) to assign origin:
| IHC marker | Tissue / tumour of origin |
|---|---|
| CK7+/CK20− | Lung, breast, thyroid, ovary, pancreas |
| CK7−/CK20+ | Colorectal carcinoma |
| CK7+/CK20+ | Urothelial, pancreatic, some gastric |
| TTF-1 | Lung adenocarcinoma, thyroid |
| PSA / NKX3.1 | Prostate |
| Thyroglobulin | Thyroid (follicular/papillary) |
| ER/PR, GATA3, GCDFP-15 | Breast |
| CDX2 | GI (colorectal) |
| PLAP, OCT3/4, SALL4 | Germ cell tumours |
| HMB-45, Melan-A, S-100, SOX10 | Melanoma |
High-yield: CK7 / CK20 panel is the workhorse first step in CUP — CK20+ / CK7− strongly favours colorectal carcinoma, whereas CK7+ / CK20− points to lung/breast/ovary. TTF-1 confirms lung adenocarcinoma; PSA/NKX3.1 confirms prostate.
High-yield: PET/CT is the investigation of choice to detect an occult primary and to assess whole-body metastatic burden in many solid tumours.
Management / drug of choice (principles)
Treatment is largely systemic and palliative, individualised by primary type and biology:
- Systemic therapy — chemotherapy, targeted agents, hormonal therapy (e.g. tamoxifen/aromatase inhibitors for ER+ breast; GnRH analogues / anti-androgens for prostate), immunotherapy (checkpoint inhibitors for melanoma, lung, RCC).
- Bone metastasis supportive care — bisphosphonates (zoledronic acid) or denosumab (anti-RANKL) to reduce skeletal-related events and treat hypercalcaemia; local radiotherapy for painful deposits.
- Brain metastasis — surgery/stereotactic radiosurgery for limited disease; whole-brain RT for multiple; dexamethasone for oedema.
- Spinal cord compression (oncologic emergency) — high-dose dexamethasone immediately + MRI whole spine + urgent RT or surgical decompression.
- Oligometastatic disease — selected resection/ablation (e.g. solitary liver or lung metastasis from colorectal cancer) can be curative-intent.
High-yield: Malignant spinal cord compression is an emergency — start IV dexamethasone without delay, then obtain MRI of the whole spine and arrange radiotherapy/surgery. Do not wait for imaging to give steroids.
Complications
- Hypercalcaemia of malignancy — from osteolysis or PTHrP; most common metabolic emergency in cancer.
- Pathological fractures and spinal cord compression.
- Malignant effusions — pleural, pericardial (tamponade), ascites.
- Liver failure / obstructive jaundice from hepatic deposits.
- Marrow failure — anaemia, leucoerythroblastic picture.
- Lymphangitis carcinomatosa — diffuse lymphatic infiltration of lung → severe dyspnoea.
- Raised intracranial pressure / seizures from brain deposits.
Key differentials
- Metastasis vs primary tumour at the site — IHC, imaging pattern (multiple lesions, grey–white junction in brain favour metastasis).
- Krukenberg tumour vs primary ovarian carcinoma — Krukenberg is bilateral with signet-ring cells in cellular stroma; primary mucinous ovarian tumours are usually unilateral, larger, no signet-ring infiltration.
- Lytic met vs multiple myeloma — myeloma: cold bone scan, M-band, Bence-Jones proteinuria, plasma cells on marrow.
- Cannonball lung lesions — RCC, choriocarcinoma, sarcoma, endometrial carcinoma.
- Reactive vs metastatic lymph node — cytology/biopsy; sentinel node assessment.
Recently asked / exam angle
- Krukenberg tumour — most common primary (stomach), histology (signet-ring cells in mucin-rich stroma), bilaterality, and route (transcoelomic ± lymphatic). Repeatedly tested.
- Virchow node = left supraclavicular, Troisier sign, drains via thoracic duct, classic primary = gastric carcinoma.
- Sister Mary Joseph nodule — periumbilical metastatic deposit.
- Osteoblastic metastasis = prostate (single-best-answer staple); osteolytic = RCC/thyroid/myeloma.
- Follicular thyroid → haematogenous; papillary → lymphatic.
- Most common route for carcinoma = lymphatic; for sarcoma = haematogenous.
- Loss of E-cadherin as the key step in EMT/invasion.
- CK7/CK20 IHC for cancer of unknown primary; CK20+CK7− = colon.
- Seed and soil hypothesis — Paget; explains organ tropism.
- Batson vertebral venous plexus — prostate/breast spine metastasis.
- Multiple myeloma — cold bone scan (use skeletal survey/MRI).
Rapid revision
- Metastasis is the single most reliable hallmark of malignancy; gliomas and BCC invade but rarely metastasise.
- Four routes: lymphatic, haematogenous, transcoelomic, implantation — carcinomas favour lymphatic, sarcomas favour haematogenous.
- E-cadherin loss drives detachment and EMT; MMPs degrade ECM; tumour cells shelter with platelets in blood.
- Liver and lung are the commonest haematogenous sites (portal vs caval drainage).
- Virchow node = left supraclavicular = Troisier sign; classic primary = stomach.
- Sister Mary Joseph nodule = periumbilical metastasis; Blumer shelf = pouch of Douglas deposit on PR.
- Krukenberg tumour = bilateral ovarian signet-ring metastasis, usually from stomach, transcoelomic spread.
- Prostate → osteoblastic (sclerotic) bone mets; RCC, thyroid, lung, myeloma → osteolytic; breast = mixed.
- Multiple myeloma = cold bone scan — screen with skeletal survey/MRI, not Tc-99m scan.
- Follicular thyroid = haematogenous (bone/lung); papillary thyroid = lymphatic (nodes).
- Batson plexus explains prostate/breast metastasis to the spine; vertebral column is the commonest skeletal site.
- PET/CT finds the occult primary; CK7/CK20 + TTF-1/PSA/CDX2 IHC panel assigns origin (CK20+CK7− = colon).