Carcinoma in situ of rectum

This code signifies the presence of abnormal, non-invasive epithelial cells confined to the mucosa of the rectum, exhibiting features of malignancy but without invasion through the basement membrane. It represents a pre-invasive stage of colorectal cancer, often referred to as high-grade dysplasia or intraepithelial neoplasia.

Apply this code when documentation explicitly states "carcinoma in situ of rectum," "intraepithelial neoplasia, high-grade, rectum," or "severe dysplasia of rectum" based on biopsy or pathology reports. This diagnosis indicates that the cancerous cells are localized and have not spread beyond the superficial layer.

• Differentiate from invasive rectal carcinoma (154.1) where malignant cells have penetrated the basement membrane.
• Ensure pathology reports clearly specify "in situ" or "non-invasive" to support this code.
• Do not use for benign polyps or low-grade dysplasia of the rectum.