Grading and staging of cancer

1. Overview

Grading and staging both quantify a malignancy, but answer different questions: grading = how aggressive does the tumor look? (histology); staging = how far has it spread? (extent). Staging is generally the more important prognostic factor.

2. Grading — differentiation/anaplasia

Based on degree of differentiation (resemblance to tissue of origin), anaplasia, and mitotic rate.

Grade	Differentiation	Anaplastic cells
GX	Cannot be assessed	—
G1 (low)	Well-differentiated	<25%
G2 (intermediate)	Moderately differentiated	25–50%
G3 (high)	Poorly differentiated	50–75%
G4 (high)	Poorly differentiated / anaplastic	>75%

• Well-differentiated → better prognosis; anaplastic → worse.

3. Staging — TNM

Component	Meaning
T (T0–T4, Tis)	Primary tumor size / local invasion depth (Tis = carcinoma in situ)
N (N0–N3)	Regional lymph node involvement
M (M0/M1)	Distant metastasis

Stages combine TNM: Stage I (T1–T2 N0 M0, ~93% survival) → Stage IV (any T, any N, M1) — surgery for I–III, chemotherapy for IV.

4. Key principle

• Metastasis (M1) = malignant by definition and upstages disease to IV regardless of T/N. Stage at diagnosis usually guides treatment and predicts outcome more reliably than grade.

💡 High-yield: Grade = histologic differentiation/anaplasia/mitoses (G1 well → G4 anaplastic). Stage = TNM (Tumor, Node, Metastasis) = extent of spread — usually the stronger prognostic factor. M1 metastasis upstages to IV. Tis = carcinoma in situ.