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Atypical Squamous Cells (ASC)
Atypical Squamous Cells of Undermined Significance (ASC-US)
Atypical Squamous Cells - Cannot Exclude HSIL (ASC-H)

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Atypical squamous cell (ASC-US)


Atypical squamous cell (ASC-US)


Colposcopy from above patient


Cervical biopsy from above patient, showing low grade SIL

A report of ASC (Atypical Squamous Cells) is the way the cytologist tells you that there is something on the patient's Pap smear that is not perfectly normal, but they can't tell with any certainty what it is or whether or not it is significant. ASC Paps are subdivided into two types:

  • ASC-US (undetermined significance)
  • ASC-H (cannot exclude high-grade SIL)

Among the women with ASC are a few with high-grade lesions of the cervix:

  • Between 5% and 17% of women with ASC-US will have a high grade SIL present (CIN 2 or CIN 3)
  • Between 24% and 94% of women with ASC-H will have a high grade SIL
  • The risk of invasive cancer of the cervix is about 0.1% to 0.2% among women with any ASC Pap.

Several approaches to management of the patient with ASC are acceptable, among them are:

  1. Immediate colposcopic evaluation
  2. Repeat Pap smear in 4-6 months with colposcopic evaluation of those with persistently abnormal findings. For those without persistence of the abnormality, close followup is usually recommended because of the known error rates of screening Pap smears.
  3. Reflex testing of the Pap smear for the presence of high-risk HPV subtypes. Patients with high risk HPV undergo colposcopy. Patients without high risk HPV are followed closely.
  4. If the patient has previously been evaluated for an abnormal Pap and found to have either mild dysplasia or HPV changes, the occurrence of an occasional ASC-US smear is not surprising and is often considered normal for that person. In higher risk circumstances, further colposcopy is sometimes undertaken to re-evaluate the cervix.
  5. A patient with a history of cervical dysplasia, who has had many normal Pap smears following treatment, and who develops ASC-US should probably be re-evaluated colposcopically if she has not had that procedure done recently, as this could represent the beginning of a new problem.

Military Obstetrics & Gynecology
2003, 2004, 2005, 2006 Medical Education Division, Brookside Associates, Ltd.
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