## Histological Types of Colorectal Cancer **Key Point:** Adenocarcinoma (including all subtypes) accounts for >95% of all colorectal cancers. Within adenocarcinomas, the tubular/enteric subtype is most common (~70%), followed by mucinous (~10–15%) and signet-ring cell (<5%) variants. ### Histological Distribution | Histological Type | Frequency | 5-Year Survival | Key Features | |-------------------|-----------|-----------------|---------------| | Adenocarcinoma (tubular/enteric) | 70–75% | 60–65% | Well-differentiated; glandular pattern | | Mucinous adenocarcinoma | 10–15% | 45–55% | Worse prognosis; mucin-rich; T4 at diagnosis | | Signet-ring cell carcinoma | 1–5% | 20–30% | Poorest prognosis; diffuse infiltration | | Neuroendocrine carcinoma | <1% | Variable | Rare; aggressive; often metastatic | | Squamous cell carcinoma | <1% | Poor | Extremely rare | | Lymphoma (MALT, DLBCL) | 1–2% | Variable | Non-epithelial; different treatment | **High-Yield:** Adenocarcinoma is the overwhelmingly dominant histological type. When the question asks for "the most common histological type," the answer is adenocarcinoma unless the stem specifies a subtype. **Clinical Pearl:** Mucinous and signet-ring cell variants are associated with worse prognosis and are often diagnosed at advanced stages (T4, Stage III–IV). They carry higher risk of peritoneal carcinomatosis. ### Adenocarcinoma Subtypes (WHO Classification) 1. **Tubular/Enteric (70–75%)** — Most common; best prognosis 2. **Mucinous (10–15%)** — Worse prognosis; signet-ring cells may be present 3. **Signet-ring cell (<5%)** — Poorest prognosis; diffuse infiltration 4. **Serrated (5–10%)** — Intermediate prognosis; associated with MLH1 methylation 5. **Micropapillary (<5%)** — Aggressive; high T-stage at diagnosis **Mnemonic:** **TAMS** — Tubular (most common), Adenocarcinoma (overall), Mucinous (second), Signet-ring (worst prognosis).
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