International classification of diseases for oncology 3rd edition icd o 3 purpose definition used principally in tumour or cancer registries for coding the site topography and the histology morphology of neoplasms usually obtained from a pathology report. Icd o international classification of diseases for oncology international classification of diseases for oncology first revision third edition isbn 978 92 4 154849 6 icd o coverindd 1 11 21 13 850 am. Now in its third edition the international classification of diseases for oncology icd o has been used for nearly 25 years as the standard tool for coding diagnoses of neoplasms in tumour and cancer registrars and in pathology laboratories icd o is a dual classification with coding systems for both topography and morphology the topography code describes the site of origin of the neoplasm and uses the same 3 character and 4 character categories as in the neoplasm section of chapter ii icd 10. Now in its third edition the international classification of diseases for oncology icd o has been used for nearly 25 years as the standard tool for coding diagnoses of neoplasms in tumour and cancer registrars and in pathology laboratories icd o is a dual classification with coding systems for both topography and morphology the topography code describes the site of origin of the