Human Papillomaviruses and Cancer

Papillomaviruses are small tumor viruses with a genome of approximately 8000 base pairs. They are found in many different types and infect a wide range of animals (from birds to rabbits، dogs، sheep and cattle) and several primates including humans. So far، over 100 different types of human papillomavirus (HPV) have been identified، among which one-third infect epithelial cells in the genital tract. Certain strains of HPV are associated with different risk levels of the transformation into cervical tumors. The HPV types that infect the genital tract are divided into two categories: high risk and low risk. The low-risk HPVs types such as HPV-6 and HPV-11، commonly cause benign warts and low-grade premalignant lesion that regress and do not progress to cancer while the high-risk types of HPV including HPV-16، HPV-18، HPV-31، HPV-33، and HPV-45 are associated with the development of anogenital cancers and are found in more than 99% of all cervical carcinomas، with HPV16 occurring most frequently. Infection by high-risk HPVs is not limited to the genital tract، since approximately 20% of cancers of the oropharynx contain DNA from these HPV types. HPV 16، 18، and 31 are constantly associated with moderate to severe cases of cervical dysplasia and are less associated with invasive cancers of the vulva، penis، and anus. It has been demonstrated that the presence of even minimal amounts of HPV DNA is associated with an increased risk in the development of cervical cancer. HPV DNA is found in up to 100% of cervical tumors، while in cervical tissue of healthy women the figure is typically below 10%. In this study we tried to investigate the role of HPV in human cancer.