Differential Diagnosis for Atypical Squamous Cells of Undetermined Significance (ASC-US)

Single Most Likely Diagnosis

• Benign cellular changes or reactive cellular changes: This is often due to inflammation, infection, or other non-neoplastic processes that can cause cellular atypia without being indicative of a precancerous or cancerous condition.

Other Likely Diagnoses

• Low-grade Squamous Intraepithelial Lesion (LSIL): ASC-US can sometimes be a precursor or associated with LSIL, which includes conditions like cervical dysplasia or human papillomavirus (HPV) infection.
• High-grade Squamous Intraepithelial Lesion (HSIL): Although less common than LSIL, a small percentage of ASC-US results can be associated with HSIL, which has a higher risk of progressing to cancer if left untreated.

Do Not Miss Diagnoses

• Cervical Cancer: Although rare, it is crucial not to miss a potential case of cervical cancer. ASC-US can occasionally be associated with more severe underlying pathology, including adenocarcinoma or squamous cell carcinoma of the cervix.
• Adenocarcinoma in situ (AIS): This is a rare but significant condition that can progress to invasive adenocarcinoma of the cervix. AIS might not always be detected through cytology alone, making follow-up and further testing critical.

Rare Diagnoses

• Other types of cancer (e.g., glandular cell abnormalities): While extremely rare, other types of cancer or precancerous conditions affecting the cervix or endometrium could potentially present with atypical cytology results.
• Metastatic disease to the cervix: This is exceedingly rare but could potentially cause atypical cells to be seen on a Pap smear, especially in patients with a known history of cancer elsewhere in the body.