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Cervical cancer and precursors

What is cervical cancer and what causes it?

The cervix is the part of the uterus (womb) that opens into the vagina. The cervix is covered with a special lining that doesn't exist anywhere else in the uterus. When cervical cancer occurs, it usually starts in that lining. Cancer of the cervix is a completely different disease from cancer of the rest of the uterus.

Cervical cancer used to be one of the most common cancers in Canadian women. Thanks to improvement in screening and treatment, deaths from cervical cancer have declined in the last decades.

We now know that most cervical cancers are caused by a family of viruses, the human papillomaviruses, called HPV for short. Over 40 different HPVs can infect the genitals, but not all of them lead to cancer. Some HPVs cause condylomas or genital warts; these HPVs do not cause cancer, and condylomas are not cancer precursors.

HPVs are transmitted by sexual contact. They are so common that most sexually active women will encounter them in their lifetime. Fortunately, this will be of no consequence for the vast majority of women. Our immune system can fight the virus and clear the infection.

What is a cervical cancer precursor?

Even when the lining of the cervix is infected by an HPV that has the potential to cause cancer, most of the time the lining will heal without consequences. However, in a very small number of women some cells will undergo changes which, if left untreated, may eventually become cancerous. The stage when the lining is not normal but not yet cancerous is called the precancerous stage, and the abnormal part of the lining is said to contain a cancer precursor. These cancer precursors are divided into two categories: mild and severe precancers. Most mild precancers will go away by themselves. However, some of them do progress to the severe precancer stage; thus, they need to be observed carefully. Severe precancers carry a higher risk of progressing to cancer, and for this reason they need to be treated. Treatment is usually done at the clinic, in less than 30 minutes. Lesions are taken out using one of several methods that remove or destroy the abnormal tissue. The success rate of the various treatment strategies is over 90%.

Why screen for cervical cancer and its precursors?

When screening programs started in the 1950s, cervical cancer was one of the most frequent cancers in Canadian women but, thanks to screening, it is now considered a relatively rare disease. The fact that cervical cancer has a long precancerous stage, lasting many years most of the time, makes it easier to catch it when it has not yet reached the full cancer stage. This is the main reason why screening is so important.

Precancerous lesions do not produce symptoms, so the only way to find them is for the doctor to "look" for them with a screening test. The treatment options for precancers and early cancers are highly effective, simple, and preserve the ability to bear children. When there was no screening for cervical cancer women presented to their doctors with symptoms, which meant the cancer was in late stages. Major surgery and radiotherapy were the only treatment options. Many cancers were found only when it was too late.


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