Morphology — Numerical List

The morphology section of ICD-O, First and Second Editions, has been revised in ICD-O-3. New terms have been added and the non-Hodgkin lymphoma and leukemia sections have been revised on the basis of the WHO Classification of Hematopoietic and Lymphoid Diseases (21, 22). The numerical list displays the structure of the coded morphology nomenclature and constitutes the primary point of reference for retrieval or decoding.

In revising the morphology section, every effort has been made to include new terms that have appeared in the recent literature. In several instances the terms for neoplasms from more than one classification scheme have been included, for example malignant lymphomas (M-959 through M-971). It should be stressed that ICD-O is a coded nomenclature and not a classification scheme for neoplasms; the listing of terms from different classifications does not represent endorsement of any particular one.

Morphology terms have five-digit codes ranging from M-8000/0 to M-9989/3. The first four digits indicate the specific histologic term (Table 8). The fifth digit, after the slash or solidus (/), is a behavior code, which indicates whether a tumor is malignant, benign, in situ, or uncertain whether malignant or benign.

Table 8. Structure of a Morphology Code

A separate one-digit code for histologic grading or differentiation is provided. For a lymphoma or leukemia, this element of the code is used to identify T-, B-, Null-, and NK-cell origin.

A complete ICD-O code thus requires 10 digits or characters to identify the topographic site (4 characters), morphologic type (4 digits), behavior (1 digit), and grade or differentiation of a neoplasm or its equivalent in leukemias and lymphomas (1 digit). Table 10 provides an example of the structure of a complete code.