Atypical squamous cells of uncertain significance

• In the majority of smears, the distinction between benign epithelial cells and neoplastic cells  can be made by an experienced cytotechnologist or cytopathologist with a high degree of confidence and the smears can be classified as  “LSIL” or “HSIL” in accordance with The Bethesda System
• However in a small proportion of cases there may be genuine doubt as to whether the epithelial cells are benign or  neoplastic.
• In accordance with The Bethesda System such smears are classified as  containing “atypical squamous cells of undetermined  significance (ASCUS)”.
• Alternative terminology (Equivalent terminology) for such smears  includes “Squamous cell atypia not definitely neoplastic “ and   “Borderline nuclear changes not amounting to neoplastic change”
• There are two situations in which the ASCUS category applies:
  • In association with HPV changes. (koilocytotic atypia)
  • In smears in which it is genuinely difficult to distinguish benign, reactive or degenerative change from LSIL , HSIL or invasive cancer
• Follow up  studies of ASCUS cases   by colposcopy, biopsy or repeat cytology have shown that they comprise a diverse group of cases. In 50-60% no significant abnormality is found whereas CIN2 or CIN3 has been reported in up to  20% of cases. These findings indicate that  women with an ASCUS smear must be carefully followed up.
• ASCUS and Human papillomavirus infection:
  • Koilocytes  and the dyskeratotic cells associated with HPV infection almost always show nuclear changes amounting to ASCUS or CIN1 (LSIL).
  • Occasionally koilocytes with markedly abnormal nuclei which are consistent with CIN2/3(HSIL) can be seen
  • Smears containing squamous cells showing the morphological changes a associated with  HPV infection should be classified according to the most severe nuclear abnormality in the smear.

Cytological features of Atypical Squamous Cells of Undetermined Significance (ASCUS)