From which tissue does signet‑ring cell carcinoma originate, and what are its clinical manifestations based on its location, type, and classification?

Signet Ring Cell Carcinoma: Tissue Origin and Clinical Manifestations

Signet ring cell carcinoma (SRCC) is an adenocarcinoma that originates from epithelial glandular tissue, most commonly arising from the gastric mucosa (stomach), but can also develop in the colorectum, appendix, breast (as lobular carcinoma), and rarely the lung.

Tissue of Origin

SRCC derives from epithelial cells with glandular differentiation that produce abundant intracellular mucin, which displaces the nucleus to the periphery creating the characteristic "signet ring" appearance 1, 2. The cell of origin varies by anatomic location:

• Gastric SRCC: Arises from gastric mucosal epithelium, classified as a "poorly cohesive" adenocarcinoma subtype in the WHO classification 1
• Colorectal SRCC: Originates from colonic/rectal glandular epithelium 3, 4
• Hereditary Diffuse Gastric Cancer (HDGC): Associated with CDH1 germline mutations, with precursor lesions including in situ SRCC and pagetoid spread of signet ring cells within the basal membrane 2
• Breast: Manifests as invasive lobular carcinoma in CDH1 carriers 2
• Appendiceal: Arises from appendiceal mucinous epithelium 5

Classification Systems

Gastric SRCC Classification

The WHO classification recognizes SRCC as a subtype of poorly cohesive adenocarcinoma 1. The Laurén classification categorizes it under the diffuse subtype 1, 6.

Key pathological features in gastric SRCC 2:

• Precursor lesions (in CDH1 carriers): In situ SRCC and pagetoid spread
• Early lesions: Tiny foci of signet ring cells confined to superficial lamina propria
• Advanced disease: Linitis plastica pattern with diffuse wall infiltration, cords, microglands, and mucin lakes

Macroscopic Classification

• Early gastric cancer: Paris classification (0-I protruded, 0-II superficial, 0-III excavated) 1
• Advanced gastric cancer: Borrmann classification, with SRCC typically presenting as Type IV (diffusely infiltrative with wall thickening) 1

Clinical Manifestations by Location

Gastric SRCC

Demographics and presentation 6, 7:

• Younger age at diagnosis (mean 48 years vs. 62 years for non-mucinous adenocarcinoma)
• No significant sex predilection in early disease; mixed findings in advanced disease
• Often presents with advanced stage due to horizontal submucosal spread

Stage-specific characteristics 6, 7:

• Early gastric cancer (EGC): Similar prognosis to other histotypes; no survival difference
• Advanced gastric cancer (AGC): Significantly worse prognosis than differentiated types; 5-year survival 23-31% in various studies
• Metastatic disease: Poorer outcomes with immunotherapy (ORR 31.3% vs. 50.7% in non-SRCC) 8

Molecular features 1:

• Lower HER2 overexpression (10-20% overall, less common in diffuse/SRCC types)
• Associated with genomically stable (GS) subtype in TCGA classification
• CDH1 mutations in hereditary cases 2

Colorectal SRCC

Clinical characteristics 3, 9, 4:

• Incidence: 0.1-2.4% of colorectal cancers (1.39% in one series)
• Age: Significantly younger (mean 48 years vs. 63 years for non-mucinous)
• Location: Proximal colon preference; 46% in lower rectum when rectal
• Tumor size: Larger tumors (mean 5.68 cm vs. 3.76 cm for non-mucinous)
• Stage: 90% present with TNM stage III-IV disease

Metastatic patterns 9, 4:

• Lymphatic spread: Higher rate (44.4% vs. 12.3% in non-mucinous stage IV)
• Hematogenous spread: Lower rate (18.5% vs. 69% in non-mucinous)
• Peritoneal seeding: Intermediate rate (22.2% vs. 2.7% in non-mucinous, 43.5% in other mucinous)
• Peritoneal metastasis is the critical poor prognostic factor 4

Molecular profile 3:

• Reduced mutations in WNT/β-catenin, RAS/RAF/MAPK, PI3K/AKT/mTOR pathways
• Increased alterations in RNF43, CDH1, SMAD4, and TGF-β pathway
• Two molecular subtypes:
  • MSI-H/CIMP+/BRAF+/PD-L1+: Proximal colon, potential immunotherapy candidates
  • MSS subtype: More common distally

Prognosis 9, 4:

• 5-year overall survival: 0-46% (typically 23-30%)
• Stage III R0 resection: 5-year disease-free survival 30.3%
• Curative resection rates lower (21-82% vs. higher in other types)

Appendiceal SRCC

Critical prognostic distinction 5:

• Signet ring cells within mucin pools only: 5-year OS 35.8% (similar to high-grade mucinous without signet rings)
• Signet ring cells invading tissue: Median OS 0.5 years vs. 2.4-2.9 years (p=0.03-0.04)
• Report tissue invasion specifically when present

Primary Pulmonary SRCC

Extremely rare presentation 10:

• Subtype of lung adenocarcinoma
• Aggressive behavior
• Early diagnosis and active treatment associated with prolonged survival
• Limited data available

Key Clinical Pitfalls

1. Endoscopic detection difficulty: SRCC spreads horizontally in submucosa with minimal mucosal changes, making endoscopic diagnosis challenging 2, 11

2. Staging underestimation: Consider exploratory laparoscopy to detect peritoneal metastases, especially in colorectal SRCC 4

3. Histological heterogeneity: Gastric SRCC shows significant intratumoural heterogeneity 1; ensure adequate sampling

4. Age-appropriate screening: Consider HDGC genetic testing (CDH1, CTNNA1) in young patients with diffuse gastric cancer or family history 1, 2

5. Treatment selection:

   • Peritoneal metastasis predicts poor immunotherapy response in gastric SRCC (PFS 6.6 vs. 13.6 months without peritoneal disease) 8
   • Cytoreductive surgery with HIPEC should be highly selective in colorectal SRCC with peritoneal disease 4

6. Prophylactic gastrectomy: In CDH1 carriers, total gastrectomy with confirmed squamous esophageal and duodenal margins; D1 lymphadenectomy sufficient (D2 not required for true prophylactic cases) 2