Topic
Viral Oncogenesis
How some viruses cause cancer: direct oncogenesis through viral oncoproteins that disable the cell's growth controls, and indirect oncogenesis through chronic inflammation and failed immune surveillance. The shared biology, and the tumour viruses that drive it.
Viral oncogenesis is the process by which infection with a virus contributes to cancer. It is a large and preventable share of the cancer burden: infectious agents cause roughly 13 per cent of cancers worldwide, and oncogenic viruses account for the majority of that, more than one in ten of all cancers. The burden falls hardest on low- and middle-income countries, so it weighs more heavily in South Africa than in high-income settings, driven here above all by human papillomavirus and the cancers of advanced HIV.
Seven viruses are currently recognised as primary human oncoviruses capable of driving cellular transformation. Six of these agents utilise direct mechanisms of oncogenesis, such as genomic integration or the expression of viral oncoproteins that actively dysregulate the host cell cycle. The seventh, HCV, operates strictly via indirect mechanisms, driving oncogenesis through chronic inflammation, oxidative stress, and relentless cycles of hepatocyte regeneration. Parallel to these primary agents is the human immunodeficiency virus (HIV), which is also a recognised human carcinogen despite carrying no viral oncogene itself. Rather than initiating cellular transformation, HIV acts as a profound, indirect promoter by dismantling the host immune surveillance networks that would otherwise hold these primary oncoviruses in check. The distinction that organises the whole topic is between direct oncogenesis, where a viral oncoprotein disables the cell’s growth controls from within, and indirect oncogenesis, where chronic inflammation or failed immune surveillance creates the conditions for cancer.
| Virus | Family; genome | Principal cancers | Mechanism |
|---|---|---|---|
| Human papillomavirus (HPV), high-risk types | Papillomaviridae; dsDNA | Cervical (near 100 per cent), other anogenital, oropharyngeal | Direct (E6, E7) |
| Hepatitis B virus (HBV) | Hepadnaviridae; reverse-transcribing DNA | Hepatocellular carcinoma | Mixed (HBx, integration, inflammation) |
| Hepatitis C virus (HCV) | Flaviviridae; positive-sense RNA | Hepatocellular carcinoma | Indirect (chronic injury, cirrhosis) |
| Epstein-Barr virus (EBV) | Orthoherpesviridae; dsDNA | Burkitt lymphoma, nasopharyngeal carcinoma, Hodgkin lymphoma, B-cell lymphomas, some gastric carcinoma | Direct (LMP1, EBNA) |
| Kaposi sarcoma-associated herpesvirus (KSHV) | Orthoherpesviridae; dsDNA | Kaposi sarcoma, primary effusion lymphoma, multicentric Castleman disease | Direct (viral mimics) |
| Human T-lymphotropic virus type 1 (HTLV-1) | Retroviridae; reverse-transcribing RNA | Adult T-cell leukaemia/lymphoma | Direct (Tax, HBZ) |
| Merkel cell polyomavirus (MCPyV) | Polyomaviridae; dsDNA | Merkel cell carcinoma | Direct (truncated large T, small t) |
| Human immunodeficiency virus (HIV) | Retroviridae; reverse-transcribing RNA | Kaposi sarcoma, lymphomas, cervical cancer, via the other viruses | Indirect (immunosuppression; no oncogene) |
The shared biology lives in a single article, Mechanisms of viral oncogenesis: direct versus indirect oncogenesis, the viral oncoprotein paradigm and the Rb and p53 pathways it targets, viral mimicry of growth and survival signalling, integration and insertional mutagenesis, the indirect routes through inflammation and immunosuppression, and why a virus is necessary but not sufficient. Each tumour virus is then covered end to end in its own profile, human papillomavirus, hepatitis B virus, hepatitis C virus, Epstein-Barr virus, Kaposi sarcoma-associated herpesvirus, human T-lymphotropic virus type 1 and Merkel cell polyomavirus, listed below.