Volume 139: Hepatitis D virus, human cytomegalovirus, and Merkel cell polyomavirus

We are pleased to announce that the results of the recent IARC Monographs evaluation of the carcinogenicity of hepatitis D virus (HDV), human cytomegalovirus (HCMV), and Merkel cell polyomavirus (MCPyV) have now been published in The Lancet Oncology.

HDV, HCMV, and MCPyV were all accorded high priority by the Advisory Group to Recommend Priorities for the IARC Monographs during 2025–2029. HDV and MCPyV were previously evaluated by the IARC Monographs in Volumes 59 and 104, respectively. HCMV was evaluated for the first time.

HDV is an RNA virus classified in the Delta virus genus (family Kolmioviridae). HDV requires hepatitis B surface antigen (HBsAg) as its envelope; therefore, establishing an HDV infection necessitates prior or simultaneous infection with hepatitis B virus. Transmission can occur through contact with infected human blood or other infected body fluids, e.g. via sharing needles, transfusion of contaminated blood products, haemodialysis, or unprotected sex. The prevalence of HDV infection within HBsAg-positive populations ranges from 1% to 10% in most regions of the world, although it is much higher in some countries.

HCMV is a beta-herpesvirus that is transmitted through body fluids such as saliva, blood, urine, semen, and breast milk, and from mother to foetus during pregnancy. Worldwide HCMV seroprevalence is estimated at 83% for the general population and is generally higher in South America, Africa, and South Asia. Infection can occur at all ages but is most common during childhood. Moreover, congenital HCMV infection, occurring in approximately 0.7% of live births, is the most common viral cause of sensorineural hearing loss and neurological disabilities in newborns.

MCPyV is a polyomavirus that has a high prevalence in human populations. Infections are typically acquired in early childhood via close contact, and the virus persists as a common component of the normal skin virome.

The Working Group evaluated HDV as carcinogenic to humans (Group 1) on the basis of sufficient evidence for cancer in humans. HDV causes hepatocellular carcinoma. The mechanistic evidence for HDV was strong for the key characteristics of carcinogens, and the evidence regarding cancer in experimental animals was inadequate.

MCPyV was also evaluated as carcinogenic to humans (Group 1) on the basis of sufficient evidence for cancer in humans and the combination of sufficient evidence for cancer in experimental animals and strong mechanistic evidence in exposed humans. MCPyV causes Merkel cell carcinoma.  

HCMV was classified as possibly carcinogenic to humans (Group 2B) on the basis of limited evidence for cancer in humans. Positive associations have been observed between HCMV and childhood acute lymphoblastic leukaemia. The mechanistic evidence that HCMV exhibits the key characteristics of carcinogens was limited and the evidence regarding cancer in experimental animals was inadequate.

The full scientific assessment will be published as Volume 139 of the IARC Monographs.

Karagas MR, Kaldor J, Michaelis M, Muchengeti MM, Alfaiate D, Argirion I, et al.

Carcinogenicity of hepatitis D virus, human cytomegalovirus, and Merkel cell polyomavirus

Lancet Oncol, Published online 27 June 2025;

https://doi.org/10.1016/S1470-2045(25)00403-6

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