Makindo Medical Notes

Oncogenic viruses are viruses capable of causing cancer by interfering with normal cellular processes such as cell cycle regulation, apoptosis, and DNA repair. These viruses often integrate their genetic material into the host genome or alter cellular signaling pathways, leading to uncontrolled cell growth and malignancy. Below is a detailed discussion of major oncogenic viruses and their associated cancers.

Oncogenic Viruses and Associated Cancers

Oncogenic Virus	Associated Cancers
HTLV-1 (Human T-cell Leukemia Virus Type 1)	Adult T-cell leukemia/lymphoma (ATLL).
HBV/HCV (Hepatitis B and C Viruses)	Hepatocellular carcinoma (HCC).
EBV (Epstein-Barr Virus)	Burkitt's lymphoma, Nasopharyngeal carcinoma, Hodgkin's lymphoma.
HHV-8 (Human Herpesvirus 8)	Kaposi's sarcoma, Body cavity B-cell lymphoma (Primary Effusion Lymphoma).
HPV (Human Papillomavirus)	Cervical cancer (types 16/18), Penile cancer, Anal cancer, Oropharyngeal cancers.

Details of Major Oncogenic Viruses

1. Human T-cell Leukemia Virus Type 1 (HTLV-1)

• Pathogenesis: HTLV-1 integrates into host DNA and promotes T-cell proliferation through the Tax protein, which disrupts cell cycle regulation.
• Associated Cancer: Adult T-cell leukemia/lymphoma (ATLL), a rare and aggressive cancer of mature T-cells.
• Transmission: Blood transfusion, sexual contact, breastfeeding.

2. Hepatitis B Virus (HBV) and Hepatitis C Virus (HCV)

• Pathogenesis: Chronic infection leads to persistent inflammation, fibrosis, and cirrhosis. Viral proteins such as HBx in HBV may disrupt tumor suppressor pathways.
• Associated Cancer: Hepatocellular carcinoma (HCC).
• Transmission: Blood, sexual contact, and vertical transmission from mother to child.

3. Epstein-Barr Virus (EBV)

• Pathogenesis: EBV infects B cells and epithelial cells, driving proliferation through latent membrane proteins (LMP1, LMP2) and EBNA (Epstein-Barr Nuclear Antigen).
• Associated Cancers:
  • Burkitt's lymphoma, especially in malaria-endemic regions.
  • Nasopharyngeal carcinoma, particularly in Southeast Asia.
  • Hodgkin's lymphoma in immunocompromised individuals.
• Transmission: Saliva (often referred to as "the kissing disease").

4. Human Herpesvirus 8 (HHV-8)

• Pathogenesis: HHV-8 encodes viral oncogenes such as vIL-6 and KSHV-GPCR, which drive angiogenesis and tumor formation.
• Associated Cancers:
  • Kaposi's sarcoma, a vascular tumor associated with AIDS.
  • Body cavity B-cell lymphoma (Primary Effusion Lymphoma).
• Transmission: Saliva, sexual contact, and organ transplantation.

5. Human Papillomavirus (HPV)

• Pathogenesis: High-risk HPV types (16, 18) produce oncogenic proteins E6 and E7, which inactivate p53 and Rb tumor suppressor proteins, respectively.
• Associated Cancers:
  • Cervical cancer (the most common HPV-related cancer).
  • Penile and anal cancers.
  • Oropharyngeal cancers, especially in the tonsils and base of the tongue.
• Transmission: Sexual contact, including oral and genital routes.

Prevention and Management

• Vaccination:
  • HBV vaccine prevents hepatitis B and reduces HCC risk.
  • HPV vaccine (e.g., Gardasil) protects against high-risk HPV types and prevents cervical and other HPV-related cancers.
• Screening: Regular cervical screening (Pap smears) for early detection of HPV-associated lesions. Liver ultrasound and alpha-fetoprotein (AFP) levels for HCC in at-risk individuals.
• Antiviral Therapy:
  • Antiretrovirals for HIV/AIDS to reduce HHV-8-associated cancers.
  • Interferon and direct-acting antivirals (DAAs) for HCV infection.
• Education and Lifestyle Modifications: Safe sex practices, reducing alcohol consumption, and smoking cessation reduce oncogenic viral risks.

References

• CDC: Cancers and Viruses
• WHO: Cancer Fact Sheet