As research in recent years has shown, a very large proportion of cervical cancers (about 95% of cases) originate from a previous infection with a Human Papilloma Virus. This virus is sexually transmitted.
Cervical cancer is the consequence of an infection with these human papillomaviruses. This cancer develops from lesions caused by these viruses of the Human Papillomavirus (HPV) family. However, not all HPV infections develop into cancer.
What is Human Papilloma Virus?
It is a family of viruses, some of which have few carcinogenic effects, but among them, viruses 16 (about 50% of this type of cancer in France) and 18 (about 20%) are very dangerous (also, but to a lesser degree because they are less present in France: viruses 31, 33 and 35). They have an important carcinogenic power, and they are responsible for a considerable percentage of cervical cancers. In some regions of the world, other human papillomaviruses will be more present, and therefore responsible for more cancers, for example in Colombia, virus 45 is responsible for half of all cervical cancer lesions.
Within this family of viruses, which includes more than one hundred different viruses (*), two subfamilies can be distinguished. Some affect the skin and others the vaginal mucous membranes. The conditions are benign, such as warts on the hand and the arch of the foot, but other conditions can develop into cancers, including cervical cancer.
In the case of an infection transmitted by sexual intercourse, most often the evolution is without consequences (condylomas: small benign formations proliferating on the vaginal mucous membrane), but sometimes there can be the development of precancerous lesions, which can themselves evolve into cervical cancer, if they are not detected and treated. For example, HPV viruses are responsible for 85-100% of cervical cancers. However, in women who are not infected with HPV, the risk of cancer is very low.
Infections with this family of viruses are very common. Among sexually active women, about 80% of them will have had contact with at least one virus from this family by the age of 50. Most often, the infection is without consequences, usually undetected by the affected person, and recovery is spontaneous after a few months. The exact process that will induce cancer is unknown, but it is currently believed that the age of the infection is what will start the cancerous process: the persistence of the infection by this oncogenic virus leads to cellular abnormalities (the most important marker of tumour).
(*) There are approximately 120 genotypes of HPV, 40 of which infect the genital epithelium, some HPVs being oncogenic (in particular HPV16 and HPV18) and may cause cervical, vulvar and anal cancer, others being non-oncogenic and may cause condylomas or venereal vegetations (in particular HPV6 and HPV11).
What are the effects induced by these viruses in case of cervico-vaginal infection?
A certain number of viruses (see above) of this family create small benign formations that will multiply on the vaginal mucosa, these are condylomata. On examination (vaginal smear), these are deformations of the vaginal cells, called dysplasia. They can be mild, moderate or severe (the latter being the first stage of a very localised cervical cancer).
Only a small number of HPV produce these cancerous lesions: in France, viruses 16, 18, 31, 33 and 35 are responsible for almost all of these lesions. Lesions on the cervix are identified by "colposcopy" (examination of the cervix with a magnifying process) and then by microscopic examination of the lesion removed by biopsy.
(In Western Europe, genotypes 16 and 18 are involved in about 73% of cervical cancers).
It is important to know:
- that not all HPV infections produce condylomata,
- that condylomas can:
- disappear naturally,
- either remain present (in this case, it is preferable to remove it by laser or other means)
- or, if not detected and eliminated, they can lead to cervical cancer. Because this transformation can be very slow, the cancer can occur several decades after contamination.
- that the risks increase with the number of sexual partners.
According to some studies, papillomaviruses are probably responsible for other cancers (larynx, skin, stomach, oesophagus, prostate, ...). Current work is investigating the exact role of HPV in different types of cancers where their responsibility is being investigated.
HPV infections are mandatory but not sufficient for the growth of lesions that will lead to cervical cancer. It appears that a combination of several factors is needed that would eventually lead to changes in cervical cells.
HPV vaccines
These are preventive vaccines, not curative. That is to say, if the woman has already been infected with the virus, it will have no effect on the subsequent development of condylomata. Therefore, vaccination is only useful and will only be recommended to women who have not had contact with HPV, i.e. before the first sexual intercourse (the use of condoms only partially protects against HPV8 infection - source http://www.hcsp.fr).
In France there are two vaccines, Cervarix (active against the two most carcinogenic types of HPC, 16 and 18) and Gardasil (active against viruses 16, 18, as well as 6 and 11). The High Council of Public Health gives preference to the quadrivalent vaccine.
Vaccination protocol: two injections one month apart and the third to the sixth month.
Warning!
The HPV vaccine does not replace regular cervical cancer screening by vaginal smear. The smear is therefore still recommended for women between 25 and 65 years of age, every 3 years, after 2 normal initial smears one year apart.