Although the cervix (the neck of the uterus as it opens into the vagina) is really part of the uterus, most cancer of the cervix is quite distinct from uterine cancer because the cells involved are very different.
The lining of the uterus is made up of glandular tissue, whereas the outer part of the cervix (the ectocervix) is covered with squamous tissue. Glandular tissue is composed of large, chunky column-type cells; squamous tissue is made up of flat cells. Squamous cell carcinoma is the most common type of cervical cancer. Adenocarcinoma of the cervix, which resembles cancer of the uterus and affects the columnar, glandular cells covering the inner part of the cervix, is the least common.
Before puberty, the cervix is covered with cube-shaped cells. Right after puberty, the cervical cells transform themselves from these columnar cells to natter squamous cells, a process technically called squamous metaplasia. If the cells being transformed during squamous metaplasia receive an insult of some kind, abnormal cells can develop later. But the impact of these abnormal changes will not show up for years, even decades. Researchers are still trying to fathom what kind of agents initiate, however slowly, cancerous changes in the cervix. Are these agents chemicals or viruses or bacteria? Scientists only know that the substances that trigger the changes are associated somehow with sexual intercourse.
Right now the leading candidate is the human papilloma virus (human papilloma virus), the same virus that causes genital warts. Often women who have cervical cancer have had episodes of genital warts, and researchers have actually been able to grow strains of the wart virus from tissue samples of women who have cervical cancer. Yet having genital warts does not necessarily lead to cervical cancer. More than seventy strains of the condyloma or papilloma virus can produce genital warts; only about three can cause cancer. Many, many women carry human papilloma virus, just as many people carry some other virus that does not necessarily make them sick. Some experts believe that 100 percent of women who are sexually active in the United States have been exposed to the human papilloma virus. Most women mount their immunological defenses and have warts at worst, but often no symptoms at all.
There are other theories about the cause of cervical cancer and the final answers are not in, except that we do know cervical cancer has something to do with sex. We just don’t know what. The older a woman is when she begins having intercourse (that is, the further she is from puberty when her cervical cells are changing), the less likely she is to get cervical cancer. Because the cells seldom change quickly from totally normal to cancerous, yearly Pap smears allow early diagnosis and treatment.