A 58-year-old man from rural Maharashtra presents with a 6-month history of progressive constipation alternating with diarrhoea, abdominal pain, and a 4 kg weight loss. On examination, a palpable mass is felt in the left lower abdomen. Colonoscopy reveals a stricturing lesion at the sigmoid colon with irregular, ulcerated mucosa. Biopsy shows infiltrating glands with marked desmoplastic stromal reaction. Which histological grade would carry the worst prognosis in this case?

Explanation

## Histological Grading & Prognosis in Colorectal Carcinoma **Key Point:** Poorly differentiated adenocarcinoma with signet-ring cell morphology represents the worst prognostic histological subtype in colorectal cancer. ### Grading System (WHO/Nottingham) | Grade | Differentiation | 5-Year Survival | Characteristics | |-------|-----------------|-----------------|------------------| | G1 | Well-differentiated | 65–75% | >95% glands formed, minimal mucin | | G2 | Moderately differentiated | 50–65% | 50–95% glands formed | | G3 | Poorly differentiated | 20–40% | <50% glands, signet-ring cells, solid sheets | | G4 | Undifferentiated | <20% | No gland formation, highly aggressive | **High-Yield:** Signet-ring cell carcinoma is a special poor-prognosis variant characterized by: - Mucin-filled cells with eccentric nuclei - Diffuse infiltration (linitis plastica pattern) - Early peritoneal spread - Frequently presents at advanced stage (Stage III–IV) - 5-year survival <15% even with chemotherapy ### Why Signet-Ring Cell Morphology is Worst 1. **Growth Pattern:** Diffuse infiltration rather than mass formation → delayed diagnosis 2. **Peritoneal Involvement:** High propensity for peritoneal carcinomatosis 3. **Lymphatic Invasion:** Extensive intramural spread 4. **Chemotherapy Resistance:** Poor response to standard 5-FU/oxaliplatin regimens **Clinical Pearl:** Signet-ring cell carcinomas often present as "leather bottle stomach" pattern in gastric primaries, but in colon they manifest as stricturing lesions with diffuse wall thickening—exactly as seen in this patient's colonoscopy. **Mnemonic: SRC (Signet-Ring Cell) = Survival Reduced Critically** - S = Signet-ring morphology - R = Resistance to therapy - C = Carcinomatosis (peritoneal spread) ### Mucinous Adenocarcinoma (Option C) While mucinous adenocarcinoma carries intermediate-to-poor prognosis (Stage-for-stage worse than non-mucinous), it is NOT as universally poor as signet-ring cell. Mucinous tumours with extracellular mucin lakes may retain some gland formation and are more chemotherapy-responsive than signet-ring variants. [cite:Robbins 10e Ch 17]