Metastatic Patterns & Cancer Epidemiology
Where cancers land, how they travel, and which ones kill most
Why Metastases Dominate Certain Organs
Metastases outnumber primaries. In adults, a malignant lesion in the brain, liver, or bone (and in the lung) is more often a metastasis than a primary tumor. Distant spread is the one feature that proves malignancy, although basal cell carcinoma and most gliomas are malignant yet rarely metastasize.
Plumbing plus soil. Circulating tumor cells arrest in the first capillary bed downstream: caval drainage leads to the lungs, portal drainage to the liver. The "seed and soil" principle adds biology; breast cancer cells bearing the chemokine receptor CXCR4, for example, home to organs rich in its ligand CXCL12 (lung, liver, marrow, lymph nodes).
Routes of Spread
Lymphatic. The default for carcinomas, which reach the regional (sentinel) node first; hence sentinel node biopsy to stage breast cancer and melanoma.
Hematogenous. The default for sarcomas (e.g., osteosarcoma, leiomyosarcoma), which invade thin-walled veins and most often seed the lungs.
- Carcinomas that use the blood: follicular thyroid carcinoma (capsular and vascular invasion; bone and lung, whereas papillary carcinoma goes to cervical nodes), choriocarcinoma, renal cell carcinoma (renal vein → IVC), and hepatocellular carcinoma (portal and hepatic veins). RCC and choriocarcinoma classically give "cannonball" lung nodules.
- Sarcomas that use nodes: rhabdomyosarcoma, synovial sarcoma, epithelioid sarcoma, clear cell sarcoma, and angiosarcoma.
Cavity seeding. Ovarian carcinoma implants over the peritoneum and omentum (omental caking) with malignant ascites. Pseudomyxoma peritonei, an abdomen filled with gelatinous mucin, usually follows rupture of an appendiceal mucinous neoplasm; mucinous ovarian lesions in these patients are usually secondary. In the CNS, medulloblastoma seeds the CSF and produces "drop" metastases.
Named metastases: Krukenberg tumor (bilateral ovarian deposits of signet-ring cell carcinoma, usually gastric), Virchow node (left supraclavicular), Sister Mary Joseph nodule (umbilicus), and Blumer shelf (rectouterine or rectovesical pouch).
Organ Patterns: Brain, Liver, Lung
| Organ | Leading primaries | Typical appearance |
|---|---|---|
| Brain | Lung > breast > melanoma, then colorectal and renal | Multiple well-circumscribed, ring-enhancing lesions at the gray-white junction with vasogenic edema |
| Liver | Colon ≫ stomach > pancreas (portal); breast, lung, melanoma (hepatic artery) | Multiple well-demarcated nodules, often umbilicated by central necrosis |
| Lung | Breast, colorectal, renal, sarcomas, choriocarcinoma | Multiple round peripheral nodules; "cannonball" lesions (RCC, choriocarcinoma) |
Brain. Emboli lodge at the gray-white junction, where arterioles narrow abruptly; lesions are circumscribed, often multiple, with edema out of proportion to their size, unlike a single infiltrative glioblastoma. Per patient, melanoma has the highest brain tropism; lung leads in total numbers only because it is so common. Hemorrhagic metastases suggest melanoma, renal cell carcinoma, choriocarcinoma, or thyroid carcinoma.
Liver. A primary liver tumor is more often a single mass (hepatocellular carcinoma usually arises in a cirrhotic liver). Liver metastases also unmask carcinoid syndrome: serotonin from a small-bowel neuroendocrine tumor escapes degradation by hepatic monoamine oxidase.
Bone Metastases
Sources and sites. Breast and prostate lead, then lung, thyroid, and kidney. Deposits favor red marrow of the axial skeleton: vertebrae (most common), pelvis, ribs, skull, and proximal femur and humerus. Metastatic carcinoma is the most common malignant tumor of adult bone.
Batson plexus. The vertebral venous plexus is valveless, so rising intra-abdominal pressure (coughing, straining) drives blood retrograde from pelvic veins into vertebral veins, carrying prostate cancer to the lumbar spine and pelvis without a stop in the lungs.
| Pattern | Typical primaries | Clues |
|---|---|---|
| Osteoblastic (sclerotic) | Prostate; small cell lung carcinoma | Dense lesions; ↑alkaline phosphatase |
| Osteolytic | Renal cell, thyroid, non-small cell lung carcinoma; melanoma | Hypercalcemia, pathologic fracture |
| Mixed | Breast | Features of both |
Lytic mechanism. Tumor PTHrP and cytokines induce osteoblast RANKL, activating osteoclasts; resorbed matrix releases TGF-β that feeds the tumor. Denosumab (anti-RANKL antibody) and bisphosphonates reduce pain, fracture, cord compression, and hypercalcemia.
Bone scans detect osteoblastic activity, so purely lytic lesions (renal cell carcinoma, thyroid carcinoma, multiple myeloma) can be missed.
US Cancer Epidemiology
| Ranking | Men | Women | Both sexes |
|---|---|---|---|
| Incidence | Prostate > lung > colorectal | Breast > lung > colorectal | Breast, prostate, lung, colorectal |
| Deaths | Lung > prostate > colorectal | Lung > breast | Lung > colorectal > pancreas |
Adults. Lung cancer overtook breast cancer as the leading cancer killer of US women in 1987. Pancreatic cancer ranks third in deaths despite far lower incidence because it is usually found late. Nonmelanoma skin cancer (chiefly basal cell carcinoma) is the most common cancer overall but is excluded from registry counts.
Children. Leukemia (mostly acute lymphoblastic leukemia) is most common, followed by CNS tumors and then neuroblastoma, the most common extracranial solid tumor of childhood. Brain tumors now cause more pediatric cancer deaths than leukemia.