A 58-year-old man from rural Maharashtra presents with a 4-month history of alternating constipation and diarrhoea, along with blood-stained stools. He reports a 6 kg weight loss over the past 3 months. On examination, a palpable mass is felt in the left lower abdomen. Colonoscopy reveals a stricturing lesion at the sigmoid colon with irregular edges and friable mucosa. Biopsy shows adenocarcinoma. CT abdomen demonstrates the tumour invading the muscularis propria but not penetrating the visceral peritoneum; regional lymph nodes are enlarged but distant metastases are absent. What is the TNM stage of this tumour?

Explanation

## TNM Staging of Colorectal Carcinoma ### Tumour (T) Assessment **Key Point:** The tumour invades the muscularis propria but does NOT penetrate the visceral peritoneum (peritoneal surface). This defines **T3** disease. - T1: Invades submucosa - T2: Invades muscularis propria - T3: Invades through muscularis propria into subserosa/non-peritonealised pericolic tissues - T4a: Invades visceral peritoneum - T4b: Invades adjacent structures ### Node (N) Assessment **Key Point:** Enlarged regional lymph nodes are present on imaging. This indicates **N1** disease (1–3 regional lymph nodes involved). - N0: No regional lymph node metastasis - N1: 1–3 regional lymph nodes involved - N2: ≥4 regional lymph nodes involved ### Metastasis (M) Assessment **Key Point:** Distant metastases are absent, so **M0**. ### Overall Stage Assignment T3N1M0 corresponds to **Stage IIIA** according to AJCC 8th edition staging for colorectal carcinoma. | Stage | T | N | M | | --- | --- | --- | --- | | Stage IIA | T3 | N0 | M0 | | **Stage IIIA** | **T3** | **N1** | **M0** | | Stage IIB | T4a | N0 | M0 | | Stage IIIB | T4a | N1–N2 | M0 | **Clinical Pearl:** Sigmoid colon tumours with altered bowel habits and weight loss are classic presentations of left-sided colonic obstruction. The presence of lymph node involvement upstages the tumour from Stage IIA to Stage IIIA, which mandates adjuvant chemotherapy post-surgery. **High-Yield:** Stage III colorectal cancer (any T, N1–N2, M0) requires both surgery and adjuvant chemotherapy (5-FU/LV ± oxaliplatin) for optimal survival.