Correct Answer: A. Cholangiocarcinoma
Clonorchis sinensis (Chinese liver fluke) is a trematode endemic in Southeast Asia, including parts of India (Assam, Northeast regions), acquired through consumption of raw or undercooked freshwater fish. The adult worms reside in the bile ducts and cause chronic inflammation through mechanical irritation, toxic metabolite release, and repeated epithelial injury. This chronic cholangitis leads to cholangiocarcinoma (bile duct adenocarcinoma), making it a WHO Group 1 carcinogen. The pathophysiology involves persistent epithelial regeneration in response to parasitic damage, increasing mutation risk. Clonorchis sinensis is one of only three parasites definitively linked to human malignancy (alongside Opisthorchis viverrini and Schistosoma haematobium). In endemic regions like Thailand and Laos, cholangiocarcinoma incidence is 100–300 times higher than non-endemic areas. Indian clinicians must recognize this association in patients with unexplained cholangitis or bile duct strictures from endemic zones. The latency period is typically 10–30 years of chronic infection before malignant transformation.
Why the other options are wrong
B. Gastric carcinoma — While Clonorchis sinensis causes chronic cholangitis, it does not directly invade or chronically inflame the gastric mucosa. Gastric carcinoma is classically associated with Helicobacter pylori (not a parasite) and Schistosoma japonicum (which causes intestinal schistosomiasis, not gastric disease). NBE may trap students who confuse parasitic infections broadly with all GI malignancies. C. Cervical cancer — Cervical cancer is causally linked to human papillomavirus (HPV), not parasitic infections. Clonorchis sinensis has no anatomical or pathophysiological connection to the cervix. This is a distractor that tests whether students conflate parasitic carcinogens with viral carcinogens—a common NBE trap in oncology-parasitology overlap questions. D. Bladder carcinoma — Bladder carcinoma is specifically associated with Schistosoma haematobium (urinary schistosomiasis), not Clonorchis sinensis. While both are parasitic carcinogens, they target different organs: S. haematobium → bladder; C. sinensis → bile ducts. Students may confuse the two parasites if they memorize 'parasites cause cancer' without organ specificity.
High-Yield Facts
- Clonorchis sinensis is acquired by eating raw/undercooked freshwater fish; endemic in Southeast Asia and parts of Northeast India (Assam).
- Bile duct adenocarcinoma (cholangiocarcinoma) is the malignancy directly caused by chronic C. sinensis infection; WHO Group 1 carcinogen.
- Latency period for malignant transformation is typically 10–30 years of chronic parasitic infection.
- Three parasitic carcinogens in humans: Clonorchis sinensis (cholangiocarcinoma), Opisthorchis viverrini (cholangiocarcinoma), Schistosoma haematobium (bladder cancer).
- Chronic cholangitis from parasitic bile duct invasion → epithelial regeneration → increased mutation accumulation → carcinogenesis.
Mnemonics
PARASITIC CARCINOGENS (WHO Group 1) Clonorchis sinensis → Cholangiocarcinoma; Opisthorchis viverrini → Obile duct cancer; Schistosoma haematobium → Schistosomiasis → bladder cancer. Remember: Organ invaded = organ at risk for cancer.
NBE Trap
NBE pairs parasitic infections broadly with 'cancer risk' to trap students who don't know organ specificity. Students may select gastric carcinoma (confusing parasites with H. pylori) or bladder carcinoma (confusing Clonorchis with Schistosoma haematobium). The key discriminator is bile duct location of adult worms.
Clinical Pearl
In Indian practice, unexplained cholangitis or intrahepatic bile duct strictures in patients from Assam or Northeast India with a history of eating raw fish should raise suspicion for clonorchiasis. Serology (antibody detection) and stool microscopy (eggs) confirm diagnosis; praziquantel is the DOC. Early recognition prevents progression to cholangiocarcinoma.
_Reference: Jawetz, Melnick & Adelberg's Medical Microbiology Ch. 45 (Trematodes); Robbins & Cotran Pathologic Basis of Disease Ch. 7 (Infectious Diseases & Parasites)_