Human papillomavirus 18 (HPV18) is a high‑risk oncogenic human papillomavirus type. It infects mucosal epithelium and is the second most common HPV type associated with cervical cancer, particularly adenocarcinomas. The virus has a circular double‑stranded DNA genome and belongs to the Papillomaviridae family.
Virology and Oncogenic Properties
HPV18 is a member of the alpha‑7 species group. Its genome is an 8 kb circular double‑stranded DNA molecule encoding early proteins (E1, E2, E4, E5, E6 and E7) and late capsid proteins (L1 and L2). The virus infects basal epithelial cells via microabrasions and establishes episomal persistence. Viral replication is linked to epithelial differentiation, but in persistent infection the genome often integrates into host chromosomes. Integration disrupts the E2 gene and leads to uncontrolled expression of the E6 and E7 oncoproteins. HPV18 E6 promotes degradation of the p53 tumour suppressor and interacts with cellular proteins such as Bak to inhibit apoptosis, while E7 binds to and inactivates the retinoblastoma protein, releasing E2F transcription factors. These disruptions promote genomic instability, telomerase activation and malignant transformation. Compared with HPV16, HPV18 shows a higher affinity for glandular epithelium and is strongly associated with cervical adenocarcinomas. The virus also evades innate and adaptive immunity by downregulating interferon signalling and antigen presentation. Co‑factors such as smoking, long‑term hormonal contraception, multiple pregnancies and co‑infection with other sexually transmitted pathogens increase the likelihood of persistence and progression. Although most infections clear spontaneously within a few years, long‑term persistence markedly increases cancer risk.
Clinical Associations and Prevention
HPV18 is the second most frequent type found in cervical cancers worldwide, particularly adenocarcinoma of the cervix. It is also implicated in cancers of the vagina, vulva, penis, anus and oropharynx at lower frequency. Precursor lesions include adenocarcinoma in situ and high‑grade squamous or glandular intraepithelial lesions. Unlike low‑risk types, HPV18 rarely causes visible genital warts. Prevention strategies include prophylactic vaccination, cervical screening and safe sexual practices. The bivalent, quadrivalent and nonavalent HPV vaccines all incorporate the HPV18 L1 capsid protein and provide strong protection against infection and cervical precancer. Regular screening with Papanicolaou cytology and HPV DNA testing is essential because glandular lesions may be missed by Pap smears alone. Management of high‑grade lesions involves excisional procedures such as loop electrosurgical excision or cold knife conization. Condom use can reduce transmission, and smoking cessation may improve immune clearance. HPV18 is a high‑risk papillomavirus with strong oncogenic properties due to its E6 and E7 proteins. It is the second most common cause of cervical cancer and is notably associated with adenocarcinomas. Vaccination and regular screening are key measures to prevent and detect HPV18‑related disease. Related Terms: Oncogenic HPV, Cervical adenocarcinoma, E6 protein, E7 protein, HPV16