Colorectal Cancer: Extension
Critical part of TNM T1-T3 categories
– Codes 00–55: depth of invasion through wall Lumen
Muscularis propria Subserosa
The extension codes document the furthest extension of the primary tumor. Extension codes 00–55 for colon and rectum describe the depth of invasion of the primary tumor through the layers of the intestinal wall. The depth of invasion through the wall is critical to derive T categories 1–3.