Sarcomas: malignant mesenchymal tumours
How malignant tumours of fat, fibrous tissue, muscle, vessels and nerve sheaths arise, why they are named by the tissue they imitate, how they grow within compartments and spread through the blood to the lungs, and what their grade measures.
By the end, you can
- Describe the mesenchymal tissues and explain why sarcomas are named by the tissue they resemble.
- Contrast translocation-driven sarcomas with sarcomas that have complex, unstable genomes, and name the main risk factors.
- Explain how a sarcoma grows within a compartment, forms a pseudocapsule and recurs locally.
- Explain why sarcomas spread mainly through the blood to the lungs, and what a sarcoma grade measures.
- Compare sarcomas with carcinomas in origin, structure and spread.
What it is
A sarcoma is a malignant tumour whose cells show mesenchymal differentiation: they resemble fat, fibrous tissue, smooth or skeletal muscle, blood vessels, peripheral nerve sheath, cartilage or bone. Soft tissue sarcomas are rare (roughly 1 in 100 adult cancers, a larger share in children) and are classified, in the WHO Classification of Tumours (5th edition), by their line of differentiation and graded by how aggressive they look.
3 types to tell apart
- Translocation-driven (simple genome)
- One characteristic genetic change, usually a gene fusion from a balanced translocation, on an otherwise stable genome: Ewing sarcoma, synovial sarcoma, alveolar rhabdomyosarcoma, myxoid liposarcoma. Often in children and young adults.
- Complex genome
- Many chromosome gains and losses, with loss of the TP53 and RB1 pathways: leiomyosarcoma, undifferentiated pleomorphic sarcoma, pleomorphic liposarcoma, osteosarcoma. Mostly in older adults.
- Intermediate tumours
- Between benign and malignant: locally aggressive but not metastasising (desmoid fibromatosis, atypical lipomatous tumour), or rarely metastasising (dermatofibrosarcoma protuberans).
US spelling: tumours → tumors, tumour → tumor.
Normal function
Connective tissues: cells in the matrix they make
Mesenchymal tissues support and move the body. make the collagen of and , adipocytes store fat in , chondrocytes make , and smooth muscle, skeletal muscle, blood vessels and the sheaths of peripheral nerves complete the group pathologists call soft tissue.
Unlike an epithelium, these cells do not sit side by side on a basement membrane. Each cell lies in the matrix it makes (collagen, ground substance, cartilage or bone), with capillaries and thin-walled veins running between the cells. In adults most mesenchymal cells divide slowly; progenitor cells renew them when needed.
Soft tissue makes up a large part of the body, yet malignant tumours of it are rare. Benign soft tissue tumours, mostly lipomas, are far more common than sarcomas.
Underlying change · Step 1 of 4
How a sarcoma begins: two kinds of genetic change
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 9 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Underlying change · Step 2 of 4
Named by the tissue they imitate
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 9 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Disrupted function · Step 3 of 4
Growing within compartments: the pseudocapsule
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 9 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Consequences · Step 4 of 4
Spread through the blood, and what the grade measures
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 9 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Symptoms and signs
Symptoms, signs and findings
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 9 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Recap
Recap
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 9 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Self-check
Check your understanding
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 9 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .