ASC-US on a Pap smear of the cervix

by Adnan Karavelic MD FRCPC
February 9, 2023

What does ASC-US mean on a Pap smear of the cervix?

ASC-US stands for atypical squamous cells of undetermined significance. It means that abnormal cells were found on the surface of your cervix when the Pap smear was performed.

Does ASC-US on a Pap smear mean cancer?

No. ASC-US does not mean cancer. However, it can mean that a precancerous condition called low grade squamous intraepithelial lesion (LSIL) may be present in your cervix. For this reason, your doctor may recommend a follow-up Pap smear to rule out the presence of LSIL or similar conditions.

What causes ASC-US?

The changes seen in ASC-US on a Pap smear can be caused by infection with human papillomavirus (HPV), yeast, bacterial infection, inflammation, prior radiation treatment to the cervix, or hormonal changes such as those occurring around menopause.

What does ASC-US look like under the microscope?

When examined under the microscope, a Pap spear with ASC-US will contain abnormal-looking squamous cells.  Compared to the squamous cells normally found in the cervix, the squamous cells in ASC-US have larger nuclei (the part of the cell that holds the genetic material) and the cytoplasm (body of the cell) is smaller. Pathologists often describe these cells as showing an increased nuclear-to-cytoplasmic ratio. The nuclei can also be slightly darker and have irregular nuclear membranes. Pathologists describe these cells as hyperchromatic.

This image is an example of ASC-US on a Pap smear. The large pink cells in the center of the image are abnormal squamous cells.

Other helpful resources:

Choosing Wisely Canada

Cancer Care Ontario

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