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PA6.4-6 | Tumour Effects, Immunology & Laboratory Diagnosis — SDL Guide (Part 4)

Grading vs Staging — TNM System

Two distinct frameworks communicate very different information about a tumour:

Grading (histological) — how differentiated is the tumour?

Reflects biological aggressiveness (degree of dedifferentiation, mitotic activity, nuclear pleomorphism, necrosis).
Determined by the pathologist on biopsy/resection specimen.
Scale: Grade 1 (well-differentiated) → Grade 3 (poorly differentiated) → Grade 4 (undifferentiated/anaplastic).
Low grade = more closely resembles normal tissue = less aggressive. High grade = anaplastic = rapidly growing, aggressive.

Staging (clinical/radiological/pathological) — how far has the tumour spread?

Reflects extent of disease — is it confined to the primary site, lymph nodes, or distant organs?
Determined by imaging + surgical findings + pathology combined.
TNM system (AJCC/UICC):

Component	Assesses	Scale
T (Tumour)	Size/local extent of primary	T1–T4 (+ Tis = in situ, T0 = no evidence)
N (Node)	Regional lymph node involvement	N0 (none) → N1–N3 (increasing involvement)
M (Metastasis)	Distant metastasis	M0 (absent) → M1 (present)

TNM groupings → Stage I–IV:
• Stage I: Small, localised (T1N0M0) — best prognosis.
• Stage IV: Any M1 — distant metastasis — worst prognosis.

A three-panel medical infographic contrasts histological tumour grading with anatomical staging and summarizes the TNM system. — **Panel A:** Histological grading progression: Grade 1 well-differentiated, Grade 2 moderately differentiated, Grade 3 poorly differentiated, Grade 4 undifferentiated/anaplastic, nuclear pleomorphism, mitotic activity, necrosis, loss of architecture, low-grade to high-grade aggressiveness arrow.. **Panel B:** Staging overview: primary tumour, local invasion, regional lymph node involvement, distant metastasis to organ, anatomical extent of disease.. **Panel C:** TNM system summary: T for tumour size/local extent with Tis/T0 and T1-T4, N for regional lymph nodes with N0-N3, M for distant metastasis with M0-M1..

Practical distinction: A Grade 3 tumour may still be Stage I (small, no spread) and curable with surgery; a Grade 1 tumour may be Stage IV (already metastasised) and incurable. Grading and staging are independent and complementary.

SELF-CHECK

Histopathology of a resected colon tumour shows poorly differentiated adenocarcinoma with marked nuclear pleomorphism. Post-operative staging reveals: tumour invades through the muscularis propria (T3), 4 regional lymph nodes positive (N2), no distant metastasis (M0). What are the correct grade and stage grouping?

A. Grade 1, Stage II

B. Grade 3, Stage III

C. Grade 2, Stage IV

D. Grade 3, Stage IV

Reveal Answer

Answer: B. Grade 3, Stage III

Poorly differentiated = Grade 3 (high grade). T3N2M0 places this tumour in Stage III (regional lymph node involvement, no distant metastasis). Stage IV requires M1 (distant metastasis), which is absent here. This distinction matters: Stage III colon cancer is treated with surgery + adjuvant chemotherapy; Stage IV requires palliative/systemic therapy.

CLINICAL PEARL

The term 'staging laparotomy' — once routine in Hodgkin lymphoma — is largely obsolete since PET-CT provides non-invasive staging. But the concept it embodied (staging must reflect ALL sites of disease) remains essential. A surgeon who grades a tumour 'low' on biopsy but fails to stage it properly may offer curative surgery to a patient who already has micrometastases — a significant under-treatment error.