Neoplasia
Introduit| English | Sens |
|---|---|
| benign tumour/bɪˈnaɪn ˈtjuːmə/ | benign tumour |
| malignant tumour/məˈlɪɡnənt ˈtjuːmə/ | malignant tumour |
| metastasis | metastasis |
| grade | grade |
| stage | stage |
A billion cells before you can feel it
- A tumour you can just feel, about 1 cm across, already holds about a billion (10⁹) cells. It has grown silently for years.
- What matters next is whether it stays put or spreads. That single question separates benign from malignant.
Benign or malignant
- A benign tumour 良性肿瘤 looks like its tissue, grows slowly, is often encapsulated and stays local.
- A malignant tumour 恶性肿瘤 has abnormal, varied cells, grows fast, invades and can spread. Metastasis 转移 is the defining feature: benign tumours do not metastasise.
Which feature proves a tumour is malignant?
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Only malignant tumours metastasise.
The metastatic cascade
- Cells detach (E-cadherin is lost), break down the basement membrane with enzymes, enter a vessel, survive the bloodstream, leave it and colonise a new site.
- Every step is a gate. A tumour can shed about 10⁶ cells a day, yet fewer than 1 in 10,000 survive the trip.
Put the steps of metastasis in order.
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Each step is a gate most cells fail.
A tumour sheds 10⁶ cells into the blood each day, and 1 in 10,000 survives the bloodstream. How many survive each day?
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10⁶ × 10⁻⁴ = 100; most of these still fail to colonise.
Grade: how the cells look
- Grade 分级 measures how abnormal the cells look: well, moderately or poorly differentiated.
- Prostate cancer uses the Gleason score, the sum of the two commonest patterns (6–10 in modern practice), reported as Grade Groups 1–5.
Stage: how far it has reached
- Stage 分期 measures how far the tumour has spread. TNM: T1–T4 for size and local invasion, N0–N3 for lymph nodes, M0 or M1 for distant metastasis.
- Prognosis depends on stage first and grade second; treatment uses both.
Stage describes how abnormal the tumour cells look.
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That is grade. Stage describes how far the tumour has spread.
Routes predict the destination
- Carcinomas usually spread by lymph first (breast to the armpit nodes). Sarcomas spread by blood, and so do kidney and liver cancers.
- Ovarian cancer seeds across the peritoneum (transcoelomic spread). Prostate cancer reaches the spine through the valveless vertebral veins.
Match each cancer to its typical route of spread.
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The route predicts where to look first.
Worked example: how many doublings?
- (Fictional) One cell doubling n times gives 2ⁿ cells. 2¹⁰ ≈ 1,000, so 2³⁰ ≈ 10⁹: a 1 cm tumour is about 30 doublings old.
- Ten more doublings give 2⁴⁰ ≈ 10¹² cells, about 1 kg, which is often fatal. Most of a tumour's life happens before it can be detected.
How many doublings take one cell to 10⁹ cells? Give the nearest whole number.
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log₂(10⁹) ≈ 29.9, so about 30 doublings, since 2¹⁰ ≈ 1,000.
Worked example: reading TNM
- (Fictional report) Breast cancer T2 N1 M0: a tumour 2–5 cm, spread to movable nodes in the armpit, no distant metastasis.
- If a bone scan later finds a deposit, it becomes M1: stage IV, whatever the T and N.
What does T2 N1 M0 tell you?
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N1 means node spread; M0 means no distant metastasis.
Three common slips
- Mixing grade and stage. Grade is how the cells look; stage is how far the tumour has spread.
- Assuming bigger is always worse. Nodes and distant spread (N and M) count for more than size.
- Saying a benign tumour has metastasised. Metastasis is what makes a tumour malignant.
Recap
- Benign: differentiated, slow, local. Malignant: abnormal cells, invasion, metastasis.
- Cascade: detach → degrade the membrane → enter a vessel → survive → leave → colonise (fewer than 1 in 10,000 survive).
- Grade = appearance (Gleason 6–10, Grade Groups 1–5); stage = TNM extent; routes: lymph, blood and transcoelomic.