Here is a post from the National Cancer Institute, SEER Training Modules, on International Classification of Diseases for Oncology (ICD-O), third edition, morphology coding. By visiting the webpage you can read about coding for morphology. https://training.seer.cancer.gov/coding/guidelines/morphology.html Also, separately, the ICD-O by World Health Organization, has been used for nearly 35 years, principally in tumor or cancer registries, for coding the site (topography) and the histology (morphology) of the neoplasm, usually obtained from a pathology report. If you want to take a look check out: https://apps.who.int/iris/bitstream/handle/10665/96612/9789241548496_eng.pdf if the link doesn't work, enter ICD-O in your browser search engine. The differences between ICD-O and ICD-10 are on page 4 of the pdf. The snip below is on coding for Morphology. https://training.seer.cancer.gov/coding/guidelines/morphology.html Disclaimer: This guidance is to be used for an easy reference