What do the topographic codes in ICD-O begin with?

Topographic codes in the International Classification of Diseases for Oncology (ICD-O) are specifically designed to identify the location of tumors within the body. These codes consistently begin with the letter C, which stands for "Coded" and indicates that the code pertains to a specific anatomical site. Each topographic code follows this initial letter, forming a structured coding system that aligns with anatomical classifications and aids in standardized cancer registration and research.

Understanding that topographic codes denote precise locations, such as the lungs, liver, or breast, emphasizes the importance of this coding system for accurate cancer data collection and reporting. This system is essential for tumor registrars when coding cancer cases and contributes significantly to cancer surveillance and epidemiological studies.