Page 240 - Textbook of Pathology, 6th Edition

224 5. In vitro assay of specific viral gene products which supports implication of low-risk HPV types 1,2, 4 and 7 in
produce effects on cell proliferation and survival. common viral warts.
With these general comments, now we turn to specific Low-risk HPV types 6 and 11 are involved in the etiology
DNA and RNA oncogenic viruses and oncogenesis by them. of genital warts (condyloma acuminata).
Viral DNA of high-risk HPV types 16, 18, 31, 33 and 45
Specific DNA Oncogenic Viruses has been seen in 75-100% cases of invasive cervical cancer and
its precursor lesions (carcinoma in situ and dysplasia) and is
DNA oncogenic viruses have direct access to the host cell strongly implicated.
nucleus and are incorporated into the genome of the host High-risk HPVs are also involved in causation of other
SECTION I
cell. DNA viruses are classified into 5 subgroups, each of squamous cell carcinomas and dysplasias such as of anus,
which is capable of producing neoplasms in different hosts perianal region, vagina, vulva, penis and oral cavity.
(Table 8.9). These are: Papovaviruses, Herpesviruses, HPV types 5 and 8 are responsible for causing an
Adenoviruses, Poxviruses and Hepadna viruses. uncommon condition, epidermodysplasia verruciformis. The
condition is characterised by multiple skin warts and a
1. PAPOVAVIRUSES. This group consists of the papilloma
virus including the human papilloma virus (HPV), polyoma genetic defect in the cell-mediated immunity. About one-
virus and SV-40 (simian vacuolating) virus. These viruses third of cases develop squamous cell carcinoma in the sun-
have an etiologic role in following benign and malignant exposed warts.
neoplasms in animals and in humans: Some strains of HPV are responsible for causing multiple
juvenile papillomas of the larynx.
i) Papilloma viruses. These viruses were the first to be
implicated in the etiology of any human neoplasia. These In animals—
Benign warty lesions similar to those seen in humans are
viruses appear to replicate in the layers of stratified squamous produced by different members of the papilloma virus family
epithelium. More than 100 HPV types have been identified; in susceptible animals such as in rabbits by cottontail rabbit
the individual types are associated with different lesions. The papilloma virus, and in cattle by bovine papilloma virus
following examples of benign and malignant tumours are (BPV).
cited to demonstrate their role in oncogenesis:
There is evidence to suggest the association of BPV and
In humans— cancer of the alimentary tract in cattle.
HPV was first detected as etiologic agent in common skin HPV ONCOGENESIS IN HUMAN CANCER—
warts or verruca vulgaris (squamous cell papillomas) by Persistent infection with high-risk HPV types in target
Shope in 1933; the condition is infectious. Current evidence epithelial cells drives the molecular hallmarks of cancer
General Pathology and Basic Techniques

 TABLE 8.9: DNA Oncogenic Viruses.
Virus Host Associated Tumour
1. PAPOVAVIRUSES
Human papilloma virus Humans Cervical cancer and its precursor lesions, squamous cell
carcinoma at other sites
Skin cancer in epidermodysplasia verruciformis
Papillomas (warts) on skin, larynx, genitals (genital warts)
Papilloma viruses Cotton-tail rabbits Papillomas (warts)
Bovine Alimentary tract cancer
Polyoma virus Mice Various carcinomas, sarcomas
SV-40 virus Monkeys Harmless
Hamsters Sarcoma
Humans ? Mesothelioma
2. HERPESVIRUSES
Epstein-Barr virus Humans Burkitt’s lymphoma
Nasopharyngeal carcinoma
Human herpesvirus 8 Humans Kaposi’s sarcoma
(Kaposi's sarcoma herpesvirus) Pleural effusion lymphoma
Lucke’ frog virus Frog Renal cell carcinoma
Marek’s disease virus Chickens T-cell leukaemia-lymphoma
3. ADENOVIRUSES Hamsters Sarcomas
4. POXVIRUSES Rabbits Myxomatosis
Humans Molluscum contagiosum, papilloma
5. HEPADNAVIRUSES
Hepatitis B virus Humans Hepatocellular carcinoma