• Oncogenic viruses cause cancer.
  • The oncogenic viral DNA is always present in the tumor cells caused by the oncogenic virus.
  • In some tumor cells, the virus DNA gets fused into the cell chromosome.
  • In some cases, the virus DNA is also present as multiple copies of covalently closed DNA (cccDNA).
  • The protein of oncogenic viruses can be detected in tumor cells.
  • Some of the human adenoviruses are seen to be oncogenic.
  • They are can transform cells in culture and cause tumors after inoculating into animals.
  • Adenoviruses do not cause cancer in humans to date.
  • About 20 percent of cancer cases in human females and about eight percent in males are seen to be caused by viruses


Papillomavirus-linked cancers

  • Most of the infections caused by papillomavirus can result in cervical carcinoma in women.
  • It is a small DNA virus that infects mammals and birds.
  • There is approximately 100 human papillomavirus (HPV) types.
  • They are distinguished based on their DNA sequencing.
  • This virus enters the body through small cuts.
  •  It infects keratinocytes present in the skin or a mucous membrane.
  • Each type of this virus either infects the hands or the genitals.
  • It results in a wart or carcinoma.
  • Most of these infections do not become persistent.
  • The one who gets a persistent infection has a small risk of cancer
  • HPV 16 and 18 are the high-risk types of human papillomavirus(HPV).
  • The host cells of this virus i.e. keratinocytes do not divide after differentiation.
  • But when infected the virus induces keratinocyte into the S phase of the cell cycle.
  • When a cell is infected with a high-risk HPV, its division continues unchecked.
  • This eventually results in cancer.
  • HPV can also cause a rare type of skin cancer.
Human Papillomavirus (HPV) Infection: Symptoms, Causes, Risk ...

Polyomavirus-linked cancers

  • These are the same as papillomavirus.
  • JC  and BK viruses are two types of human polyomavirus known.
  • These viruses may have some roles in some cases of the human brain tumor.
Polyomaviridae ~ ViralZone page

Epstein-Barr virus-linked cancers

  • Anthony Epstein grew cell lines from the B cell tumor of a patient
  • He observed that the cells were continuously infected with a herpesvirus.
  • He named it Epstein Barr virus (EBV)
  • Nasopharyngeal carcinoma (NPC) is another tumor that is associated with EBV.
  • In both the tumors, the EBV genome is present as cccDNA.
  • Other cancers that are associated with EBV include – some cases of Hodgkin’s lymphoma, non-Hodgkin’s lymphoma in AIDS, and post-transplant lymphoproliferative disorder.
When Epstein-Barr virus becomes a chronic menace: chronic active ...




Interference in cell cycle 

  • A virus manipulates the internal environment of its host cell.
  • Through this, it gets all the requirements for its replication.
  • The control in the cell cycle is regulated by many proteins.
  • p53 and retinoblastoma protein (pRb) are the two proteins in humans that mediate the cell cycle control.
  • Oncogenic viruses produce several proteins that interact with these host proteins which results in repeated cycles of division.
  •  HPV early proteins E6 and E7 can interfere with control in the cell cycle.
  • E6 binds to p53, which leads to its degradation and E7 binds to pRb–E2F complexes, resulting in their dissociation.
  • The cell is then pushed to the S phase.

Activation of untargeted cell genes

  • Some virus proteins interact with the cell proteins that may not be the intended targets.
  • As a result, events that may be harmful to the host are triggered.
  • A virus protein pushes a cell towards a cancerous state by activating a gene that is switched off.

Damaging the immune defense

  • Interaction between host protein and protein produced by the oncogenic virus can damage the immune defenses.
  • This can lead to the development of cancer.