Paper I — 2023 January (Supplementary) (2019 Scheme) — Q6

Paper I

2023 January (Supplementary) (2019 Scheme) · 100 marks · 180 min

Question

Microbial carcinogenesis.

Q68 marksShort Essays★✓

Answer

Microbial carcinogenesis refers to the role of infectious agents (viruses, bacteria, parasites) in the initiation and promotion of malignant neoplasms.

Oncogenic DNA viruses

• HPV: E6 protein degrades p53; E7 protein inactivates Rb — implicated in cervical, anogenital, and oropharyngeal carcinoma
• HBV: Chronic hepatocyte injury/regeneration and direct integration into the host genome, promoting genomic instability — implicated in hepatocellular carcinoma
• EBV: Implicated in Burkitt lymphoma, nasopharyngeal carcinoma, some Hodgkin lymphomas, post-transplant lymphoproliferative disorders
• HHV-8: Implicated in Kaposi sarcoma, primary effusion lymphoma

Oncogenic RNA virus

• HTLV-1: Tax protein activates cellular growth pathways — implicated in adult T-cell leukaemia/lymphoma

Oncogenic RNA virus (indirect mechanism)

• HCV: Chronic inflammation and hepatocyte injury/regeneration (mechanism largely indirect, unlike HBV) — implicated in hepatocellular carcinoma

Bacterial carcinogenesis

• Helicobacter pylori: Chronic gastritis, promoting intestinal metaplasia and dysplasia — implicated in gastric adenocarcinoma and gastric MALT lymphoma

Parasitic carcinogenesis

• Schistosoma haematobium: Chronic bladder inflammation — implicated in squamous cell carcinoma of the bladder
• Clonorchis sinensis (liver fluke): Chronic biliary inflammation — implicated in cholangiocarcinoma

Common mechanisms

• Chronic inflammation and tissue regeneration, increasing the rate of DNA replication errors
• Direct viral oncogene expression interfering with tumour suppressor/growth regulatory pathways
• Immunosuppression (e.g., in HIV infection), allowing unchecked proliferation of other oncogenic virus-infected cells

Related Concepts

1. 1Chronic and Granulomatous Inflammation

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