Both the interior and exterior surfaces of your body are made up of epithelial cells. These cells form the barriers that protect organs — such as the deeper layers of the skin, the lungs, and the liver — and allow them to carry out their functions.

Koilocytes, also known as halo cells, are a type of epithelial cell that develops following a human papillomavirus (HPV) infection. Koilocytes are structurally different from other epithelial cells. For instance, their nuclei, which contain the cell’s DNA, are an irregular size, shape, or color.

Koilocytosis is a term that refers to the preasence of koilocytes. Koilocytosis can be considered a precursor to certain cancers.

On its own, koilocytosis doesn’t cause symptoms. But it’s caused by HPV, a sexually transmitted virus that can cause symptoms.

There are more than 200 types of HPV. Many types don’t cause any symptoms and clear up on their own. However, certain high-risk types of HPV have been linked to the development of epithelial cell cancers, also known as carcinomas. The link between HPV and cervical cancer, in particular, is well-established.

Cervical cancer affects the cervix, a narrow passageway between the vagina and the uterus. According to the World Health Organization (WHO), almost all cervical cancer cases are caused by HPV infections.

Symptoms of cervical cancer don’t usually appear until the cancer has progressed to an advanced stage. Advanced cervical cancer symptoms can include:

  • bleeding between periods
  • bleeding after sexual intercourse
  • pain in the leg, pelvis, or back
  • weight loss
  • loss of appetite
  • fatigue
  • vaginal discomfort
  • vaginal discharge, which may be thin and watery or more like pus and have a foul odor

HPV is also associated with cancers that affect the epithelial cells in the anus, penis, vagina, vulva, and parts of the throat. Other types of HPV don’t cause cancer, but may cause genital warts.

HPV is transmitted through sexual intercourse, including oral, anal, and vaginal sex. You’re at risk if you have sex with someone who has the virus. However, since HPV rarely causes symptoms, many people don’t know they have it. They may unknowingly pass it on to their partners.

When HPV enters the body, it targets epithelial cells. These cells are typically in the genital regions, for instance in the cervix. The virus encodes its own proteins into the cells’ DNA. Some of these proteins can trigger the structural changes that turn cells into koilocytes. Some have the potential to cause cancer.

Koilocytosis in the cervix is detected through a Pap smear or cervical biopsy.

A Pap smear is a routine screening test for HPV and cervical cancer. During a Pap smear test, a doctor uses a small brush to take a sample of cells from the face of the cervix. The sample is analyzed by a pathologist for koilocytes.

If the results are positive, your doctor might suggest a colposcopy or a cervical biopsy. During a colposcopy, a doctor uses a tool to illuminate and magnify the cervix. This exam is very similar to the exam you have with collection of your Pap smear. During a cervical biopsy, a doctor removes a small tissue sample from your cervix.

Your doctor will share the results of any tests you. A positive result may mean that koilocytes were found.

These results don’t necessarily mean that you have cervical cancer or that you’re going to get it. However, you’ll need to undergo monitoring and treatment to prevent possible progression into cervical cancer.

Koilocytosis in the cervix is a precursor for cervical cancer. The risk increases when more koilocytes resulting from certain strains of HPV are present.

A diagnosis of koilocytosis after a Pap smear or cervical biopsy increases the need for frequent cancer screenings. Your doctor will let you know when you need to get tested again. Monitoring may include screenings every three to six months, depending on your risk level.

Koilocytes are also implicated in cancers that appear in other areas of the body, such as the anus or throat. However, screening procedures for these cancers are not as well-established as those for cervical cancer. In some cases, koilocytosis is not a reliable measure of cancer risk.

Koilocytosis is caused by HPV infection, which has no known cure. In general, treatments for HPV target medical complications, such as genital warts, cervical precancer, and other cancers caused by HPV.

The likelihood of recovery is higher when cervical precancer or cancer are detected and treated early.

In the case of precancerous changes in the cervix, monitoring your risk through frequent screenings may be enough. Some women who have cervical precancer may require treatment, while spontaneous resolution is seen in other women.

Treatments for cervical precancer include:

  • Loop electrosurgical excision procedure (LEEP). In this procedure, abnormal tissues are removed from the cervix using a special instrument with a wire loop that carries an electrical current. The wire loop is used like a blade to gently scrape away precancerous tissues.
  • Cryosurgery. Cryosurgery involves freezing abnormal tissues to destroy them. Liquid nitrogen or carbon dioxide may be applied to the cervix to remove the precancerous cells.
  • Laser surgery. During laser surgery, a surgeon uses a laser to cut and remove precancerous tissues inside the cervix.
  • Hysterectomy. This surgical procedure removes the uterus and the cervix; this is usually used for women who have not had resolution with the other treatment options.

If koilocytes are found during a routine Pap smear, it doesn’t necessarily mean you have cervical cancer or are going to get it. It does mean you’ll likely need more frequent screenings so that if cervical cancer does occur, it can be detected and treated early, therefore giving you the best possible outcome.

To prevent HPV, practice safe sex. If you are 45 years old or younger, or if you have a child who is, talk to your doctor about the vaccine as further prevention against certain types of HPV.