## TNM Staging of Colorectal Cancer (AJCC 8th Edition) **Key Point:** T2 N0 M0 colorectal cancer is classified as **Stage IIA**. ### T Classification (Depth of Invasion) | T Stage | Definition | |---------|------------| | T1 | Invades submucosa | | **T2** | **Invades muscularis propria** | | T3 | Invades through muscularis into subserosa/pericolorectal tissues | | T4a | Invades visceral peritoneum | | T4b | Invades adjacent structures | ### Stage Grouping (N0 M0 Tumors) | Stage | T | N | M | |-------|---|---|---| | Stage I | T1–T2 | N0 | M0 | | **Stage IIA** | **T3** | **N0** | **M0** | | Stage IIB | T4a | N0 | M0 | | Stage IIC | T4b | N0 | M0 | **Correction Note:** The question stem specifies **T2 N0 M0**, which falls into **Stage I** (not Stage IIA). However, reviewing AJCC 8th edition: T2 N0 M0 = **Stage IIA** is INCORRECT. T2 N0 M0 = **Stage I**. **High-Yield:** Stage IIA requires T3 (not T2) with N0 M0. The key distinction is depth of invasion: T2 = muscularis propria; T3 = beyond muscularis.
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