ASC-US of the cervix

by Adnan Karavelic MD FRCPC
August 4, 2025

ASC-US stands for “atypical squamous cells of undetermined significance.” It is a term used in Pap smear results when some cells collected from the surface of the cervix appear slightly abnormal under the microscope. These changes are not completely normal, but they are also not clearly precancerous, which is why they are called “undetermined significance.”

ASC-US is one of the most common abnormal results on a Pap smear. In most cases, it does not mean cancer is present, but it may indicate the need for follow-up testing to make sure more serious changes are not missed.

Does ASC-US mean cancer?

No. ASC-US does not mean cancer. In fact, the vast majority of people with ASC-US do not have cancer or a precancerous condition. However, because ASC-US can sometimes be caused by a low-grade precancerous change called low grade squamous intraepithelial lesion (LSIL), your doctor may recommend further testing.

Follow-up may include:

  • Repeat Pap smear in 6 to 12 months.

  • HPV testing to see if high-risk types of human papillomavirus (HPV) are present.

  • Colposcopy (a closer examination of the cervix) if needed.

These steps help ensure that any significant changes are found and treated early if necessary.

What causes ASC-US?

The most common cause of ASC-US is infection with HPV, particularly in people under the age of 30.

Other causes of ASC-US include:

  • Yeast or bacterial infections.

  • Inflammation (due to irritation or trauma).

  • Hormonal changes, especially after menopause.

  • Recent childbirth or pregnancy.

  • Radiation therapy to the pelvic area.

  • Normal cellular aging or regeneration.

In many cases, the changes seen in ASC-US go away on their own without treatment, especially if caused by temporary factors like infections or inflammation.

What does ASC-US look like under the microscope?

When a pathologist examines the sample from your Pap smear under the microscope, they may see squamous cells (the cells that line the surface of the cervix) that appear slightly abnormal.

These cells may show:

  • Larger than normal nuclei (the center of the cell that holds genetic material).

  • Smaller cytoplasm (the body of the cell) compared to the nucleus.

  • An increased nuclear-to-cytoplasmic ratio (a feature commonly used to assess cell abnormality).

  • Slightly darker nuclei with irregular shapes or outlines (a feature called hyperchromasia).

These changes are not severe enough to make a diagnosis of a squamous intraepithelial lesion (a precancerous condition), which is why the result is reported as ASC-US.

What happens next?

Most people with ASC-US do not require immediate treatment. Instead, your doctor may recommend:

  • HPV testing – If the test is negative, you may return to regular screening. If the test is positive for high-risk HPV, additional follow-up may be needed.

  • Repeat Pap smear – A follow-up test is often done in 6 to 12 months to monitor any changes.

  • Colposcopy – A procedure that allows your doctor to examine your cervix more closely using a special magnifying instrument, typically performed if ASC-US is found in combination with high-risk HPV.

In most cases, ASC-US goes away on its own and never causes serious problems. However, it is important to follow your doctor’s recommendations for follow-up testing.

Questions to ask your doctor

  • What does ASC-US mean in my Pap smear?

  • Do I need an HPV test or another Pap smear?

  • Should I have a colposcopy to look at my cervix more closely?

  • What are the chances that these changes will go away on their own?

  • How often should I be screened going forward?

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