In the 1940’s, cervical cancer was the leading cause of death amongst women. In 1941, George Papanicolaou, discovered the technique of screening for cervical cancer which was aptly named the Pap smear. The United States adopted screening with the Pap test in the 1950s and by the mid-1980s cervical cancer incidence decreased by 70 percent. This is an astounding reduction in the incidence of cancer. When healthcare providers use the term Pap smear they are simply referring to the collection of cells from the cervix, which are evaluated for signs of early cancer. The Pap smear is not an evaluation of vagina or uterus or anything else for that matter. I often hear people tell me they had a Pap smear when the doctor didn’t collect a sample from the cervix. This is a pelvic exam without a pap.
The most common and important cause of cervical cancer is infection with the human papilloma virus (HPV). It has been shown that HPV is found in 99.7% of all cervical cancers. HPV is transmitted through sex and it has been estimated that 75-80% of people will be exposed to HPV infection before the age of 50. For the majority of these people, the HPV will resolve without any consequence. The HPV is a virus and usually the body can clear a viral infection on it’s own. However, for a small portion of people, a complex interaction between exposure to HPV, genes, and immune strength allows the HPV to stick around and start to make changes that can eventually turn into cancer. It has been estimated that it take an average of 15 years from the time of acquiring HPV to the development of cervical cancer. Most of the risk factors for developing cervical cancer are the same as those that increase the risk of getting HPV (having sex earlier, multiple sex partners, unprotected sex) or not clearing HPV (immunosuppression).
The pap is one test used to screen for cervical cancer and the HPV screen is another. Right now the recommendation is to perform a Pap test in all women ages 21-65 every three years or a Pap with HPV every 5 years for women age 30-65. My experience is that the majority of healthcare providers use the HPV screen along with the pap for those over 30, making the screening interval every 5 years. They specifically recommend NOT screening with an HPV screen for women under 30, meaning Paps are needed every 3 years for those under 30.
If we understand that young women are more likely to be exposed to HPV, that the majority of them will clear this without consequence, and that women under 20 are very unlikely to develop cervical cancer, it makes sense that the guidelines recommend waiting until 21 years old to start screening.
It also makes sense that we are advised not to screen for HPV in women under 30. Let me give an example to help make this clearer. Let’s say we have a 25 year old who gets an HPV screen that is positive and we decide based on this that we need to evaluate further by taking a biopsy (removing a piece of the cervix to look for possible signs of cancer). There is a very high probability that this patient will clear her HPV infection over the next 15 months. If we had waited, or avoided screening for HPV, we would have avoided exposing her to the biopsy. Biopsies or more invasive procedures can lead to problems with pregnancy, where the cervix isn’t strong enough to hold the fetus and preterm labor is more common. Therefore, for those under 30, it’s better to perform a Pap smear to look for changes in the cervical cells that might suggest a persistent HPV infection rather than screening for HPV.
Given that HPV is found in 99.7% of cancer and that it takes on average 15 years to progress to cancer, it also makes sense to wait 5 years between screening when you are doing both a Pap and HPV in women over 30. By screening more appropriately we are able to avoid exposing women to unnecessary biopsies and surgeries, avoid causing undue anxiety and save a bit on the costs.