1 ASC - atypical squamous cells. Squamous cells are the thin flat cells that form the surface of the cervix.  ASC–US - atypical squamous cells of undetermined significance. The squamous cells do not appear completely normal, but doctors are uncertain about what the cell changes mean. Sometimes the changes are related to human papillomavirus (HPV) infection (see Question 13). ACS–US are considered mild abnormalities.