User:Bfpage/draft/HPV-Associated cancers and precancers

Papilloma Virus (HPV) EM

HPV-associated cancers and precancers are those cancers that have a causal role in the majority of cervical cancers, and cancers in the mouth, throat, anus, penis, vulva and vagina. HPV infection is sexually transmitted. Long-term infections of the anus and genital tissues by some HPV types can progress to neoplasias, carcinomas, and invasive cancers in adolescents, women and men. Human papillomaviruses (HPVs) are sexually transmitted and are common infectious agents. These viruses are typically asymptomatic and resolve with no treatment. These small DNA viruses are part of a group of about 150 types. Only some types have been found to cause cancer.

Classification

Staging

Main article: Cervical cancer staging

Pathogenesis

The HPV alters the regular epithelial cell cycle, reverting terminally differentiated epithelial cells back into actively dividing cells-resuming the cell cycle. Squamous epithelia tissue has a turn over rate every few weeks. The cells of the basal reserve only divide while replacing cells directly above. The cells that are produced by the basal layer are called parabasal transit amplifying (TA) cells. The TA cells have 'committed' to differentiation, and will not revert to basal reserve cells. These TA cells divide daily for up to 80 cell division cycles and then discontinue differentiation. Each time a TA cell divides, it does so in an asymmetrical fashion, with one daughter cell remaining in the TA layer while the other migrates upward, leaving the cell cycle. This final differentiation results in the production of into spinous cells. The spinous cells make up the thickest layer of the epithelial tissue. In the case of cutaneous skin, the spinous cells develop into granulocytes. These then become superficial cells, programmed for death and are sloughed off as cornified envelopes. The virus enters basal cells through an epithelial tear. Viral replication is dependent upon the terminally differentiated cells reentering into the cell cycle during wound healing. This is the mechanism by which HPV infections stimulate unregulated cell cycling. This uncontrolled growth increases the thickness epithelial tissue layers, that results in wart growth.

Prevention

The implementation of Pap smear screening has resulted in the early detection of cell and tissue changes caused by HPV. This has reduced morbidity and mortality.

Managing sex partners

Since a high percentage of those infected with HPV lack symptoms or develop cancer, the identification of all sexual partners carrying the virus remains difficult. Typically, only the current partner is notified. The identification of those with multiple partners remains problematic.

Treatment

No consistently effective drugs for treating HPV infections are currently available. Surgical removal or ablation of infection sites is the standard treatment.

Research

Developing technologies for detecting HPV genotypes and their type-specific RNA transcripts are changing from cytology to molecular-based screening. Biomarkers are now being investigated in the staging of HPV lesions and will be important for developing treatment plans. Viral proteins during productive infections and are anticipated to help understand the triggering of the development of cancer. In addition, pharmacologic treatment of active papillomavirus infections can be developed.

Prognosis

HIV Infections are often without symptoms and are removed by the immune system. An active case of HPV is demonstrated by the presence of many open lesions. These lesions often heal and the infection appears to be subclinical and no symptoms are apparent. The virus persists after symptoms disappear. The infection can be reactivated with symptoms after the patient becomes immunocompromised or triggered by cycles of wounding and healing.

Epidemiology

Worldwide, each year there are about 500,000 new cases of cervical cancer and 275,000 deaths. In the US, HPV is found in approximately 33,000 new cases of cancer yearly in various tissues of the body. Out of these cases HPV causes about 26,800 of these cancers.