Morphology:
The morphology code records the type of cell that has become neoplastic and its biologic activity; in other words, it records the kind of tumor that has developed and how it behaves. There are three parts to a complete morphology code:
4 digits cell type (histology)
1 digit behavior
1 digit grade, differentiation or phenotype
In ICD-O morphology codes, a common root codes the cell type of a given tumor, while an additional digit codes the behavior. The grade, differentiation, or phenotype code provides supplementary information about the tumor.
Behavior:
The behavior of a tumor is the way it acts within the body. Pathologists use a variety of observations to determine the behavior of a tumor.
A tumor can grow in place without the potential for spread (/0, benign); it can be malignant but still growing in place (/2, noninvasive or in situ); it can invade surrounding tissues (/3, malignant, primary site); or even disseminate from its point of origin and begin to grow at another site (/6, metastatic).
| Code | Neoplasm |
|---|---|
| /0 | Benign |
| /1 | Uncertain whether benign or malignant |
| Borderline malignancy | |
| Low malignant potential | |
| Uncertain malignant potential | |
| /2 | Carcinoma in situ |
| Intraepithelial | |
| Noninfiltrating | |
| Noninvasive | |
| /3 | Malignant, primary site |
| /6* | Malignant, metastatic site |
| Malignant, secondary site | |
| /9* | Malignant, uncertain whether primary or metastatic site |
* Not used by cancer registries (used by some pathologists in some parts of the world)

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