Key points
- Carcinomas usually spread first by lymphatics; sarcomas usually by blood.
- GI cancers reach the liver through the portal vein.
- The sentinel node is the first node that drains the tumour.
- Limited (oligometastatic) disease, such as colorectal liver metastases, can sometimes be resected for cure.
The metastatic cascade
To spread, a cancer cell must invade through the basement membrane, enter a vessel (intravasation), survive in the circulation, leave it (extravasation) and grow in a new organ. Most cells fail. Paget’s “seed and soil” idea explains why some cancers favour particular organs.
The routes
| Route | How | Examples |
|---|---|---|
| Direct invasion | Into neighbouring tissue and organs | Rectal cancer into the bladder; T4 tumours |
| Lymphatic | To regional nodes, then beyond | Most carcinomas: breast to the axilla, stomach to the perigastric nodes |
| Blood-borne | Portal vein to the liver; systemic veins to the lungs | Colorectal to liver; sarcomas and kidney to lung; bone from breast, prostate, lung, kidney and thyroid |
| Transcoelomic | Across a body cavity | Peritoneal spread from stomach, ovary and colon: ascites, omental cake |
| Perineural | Along nerves | Pancreas, head and neck cancers: pain and recurrence |
| Implantation | Cells seeded during a procedure | Rare: needle tracks, wound or port sites |
The sentinel lymph node
The sentinel node is the first node to receive lymph from the tumour. If it is free of cancer, the rest of the basin very likely is too. Sentinel node biopsy, using a radioactive tracer and blue dye (or newer magnetic tracers), spares clinically node-negative patients with breast cancer or melanoma a full lymph node dissection and its lymphoedema.
Signs of spread to look for
- Virchow’s node (Troisier’s sign): a hard left supraclavicular node from abdominal cancer, classically gastric.
- Sister Mary Joseph nodule: an umbilical deposit.
- Blumer’s shelf: peritoneal deposits felt in the rectovesical or rectouterine pouch on rectal examination.
- Krukenberg tumour: ovarian metastasis, classically from signet-ring gastric cancer.
- Hepatomegaly with an irregular edge, ascites, bone pain, a pathological fracture, new neurology.
Oligometastatic disease
A few metastases in one organ do not always mean incurable disease. Resecting colorectal liver metastases, often with chemotherapy, gives long-term survival in a substantial proportion of selected patients. This is decided at the MDT.
Frequently asked questions
What are the routes of cancer spread?
Direct invasion, lymphatic spread, blood-borne (haematogenous) spread, transcoelomic spread across body cavities, perineural spread and, rarely, implantation.
What is a sentinel lymph node?
The first lymph node to receive lymph from a tumour. If it is free of cancer, the rest of that lymph node basin very likely is too, so a full dissection can be avoided.
Why do colorectal cancers spread to the liver?
Blood from the bowel drains through the portal vein to the liver, so the liver is the first capillary bed that cancer cells meet.
Further reading
- Paget S. The distribution of secondary growths in cancer of the breast. Lancet 1889;1:571–3.
- Lyman GH, et al. Sentinel lymph node biopsy for patients with early-stage breast cancer: ASCO guideline update. J Clin Oncol 2017;35:561–4.