🧾 Appendix tumour staging (TNM) helps describe how far the tumour has grown locally (T), whether it has spread to regional nodes (N), and whether there is distant/peritoneal spread (M). ⚠️ Important: the exact TNM details vary by histology (e.g. adenocarcinoma/mucinous neoplasms vs well-differentiated NETs), but the framework below matches the common AJCC/UICC approach used in UK cancer datasets.

🧠 Pathology nuance (high yield):
• LAMN/HAMN are staged differently in places (e.g. Tis (LAMN) exists; T1–T2 may be “not applicable” to LAMN in some systems).
• “Tumour deposits” can upgrade node stage to N1c even if nodes are negative.

🦠 Tumour (T)

TX: Primary tumour cannot be assessed.
T0: No evidence of primary tumour.
Tis: Carcinoma in situ (intraepithelial / invasion of lamina propria only).
Tis (LAMN): Low-grade appendiceal mucinous neoplasm confined to appendix (local definitions vary).
T1: Invades the submucosa.
T2: Invades the muscularis propria.
T3: Extends through muscularis propria into subserosa or mesoappendix.
T4a: Perforates / invades the visceral peritoneum (serosa).
T4b: Directly invades adjacent organs/structures (e.g. caecum/colon, small bowel, abdominal wall).

🧬 Nodes (N)

NX: Regional lymph nodes cannot be assessed.
N0: No regional lymph node metastasis.
N1: Regional node involvement (overall category).

N1a: Metastasis in 1 regional lymph node.
N1b: Metastasis in 2–3 regional lymph nodes.
N1c: Tumour deposits in periappendiceal/mesenteric fat with no positive regional nodes.

N2: Metastasis in 4+ regional lymph nodes.

🌍 Metastasis (M)

M0: No distant metastasis.
M1a: Intraperitoneal acellular mucin (mucin present without identifiable tumour cells in deposits).
M1b: Peritoneal metastasis beyond M1a (i.e. deposits contain tumour cells / cellular mucinous disease).
M1c: Metastasis to extra-peritoneal sites (e.g. liver, lung, distant nodes).

🧪 Grade (G)

GX: Grade cannot be assessed.
G1: Well-differentiated / low grade.
G2: Moderately differentiated / intermediate.
G3: Poorly differentiated / high grade.
G4: Undifferentiated (very aggressive biology).

🔎 Clinical interpretation tip: in appendiceal mucinous disease, the “M” category often reflects the biology of pseudomyxoma peritonei-acellular mucin behaves very differently from cellular peritoneal implants, so the staging deliberately separates them.

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TMN Staging tumours

🦠 Tumour (T)

🧬 Nodes (N)

🌍 Metastasis (M)

🧪 Grade (G)

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