Carcinoma in situ of anus and anal canal

This code signifies the presence of non-invasive malignant cells confined to the epithelial layer of the anus or anal canal. It represents an early stage of cancer where the abnormal cells have not spread beyond the original tissue layer. This condition is also known as high-grade dysplasia or intraepithelial neoplasia grade III (AIN III) when referring to the anal canal.

Assign this code when documentation explicitly states "carcinoma in situ" of the anus or anal canal, or "high-grade anal intraepithelial neoplasia (AIN III)" of these specific anatomical sites. This diagnosis is typically confirmed by biopsy and histopathological examination. Use this code for the primary diagnosis when the in situ carcinoma is the reason for the encounter.

• Carefully distinguish between carcinoma in situ of the anus/anal canal and carcinoma in situ of the anal margin, anal skin, or perianal skin, which are coded to D04.5.
• Do not code this alongside AIN I or AIN II (K62.82) due to the Excludes1 note; these represent lower grades of dysplasia.
• Ensure the documentation specifies "in situ" or "high-grade" to differentiate from invasive carcinoma or lower-grade dysplasia.