The Use of Synonyms
In the Second Edition of ICD-O, cases could be coded using
terms from any of the current classifications, as well as
a number of archaic terms. This made comparison of datasets
very difficult, especially where terms from multiple classifications
where used in the same dataset. ICD-O-3 incorporates terms
from the WHO systems as preferred terms for hematological
malignancies, but terms from older systems are retained to
permit universal coding and analysis of historical data. In
some cases a synonym may not be an exact equivalent of the
preferred (WHO) term, but in the judgment of experts in this
field the majority of cases would lie within the category
concerned.
Compatibility with ICD-10
In order to ensure compatibility with ICD-10, there are a
number of ways in which the Third Edition of ICD-O difers
from the structure of the WHO classification of hematological
malignancies. Separate codes have been allocated to B-cell
chronic lymphocytic leukemia and B-cell small lymphocytic
lymphoma. These are now recognized to be exactly the same
entity, and for presentation of data these categories may
therefore be combined. The same argument applies to lymphoblastic
lymphoma and acute lymphoblastic leukemia, which are now regarded
as the same disease but for which separate codes are provided.
Immunophenotypic Data
The use of cell marker studies has transformed hematopathology
and is a major element in achieving a high standard of diagnostic
accuracy. In the WHO classification, the lineage of the tumor
is almost always implicit in the diagnostic term used. For
example, a follicular lymphoma is by definition a B-cell malignancy.
The only instance where this does not apply is lymphoblastic
leukemia and lymphoblastic lymphoma, for which the lineage
(T-cell or B-cell) must be specified. This was not the case
in the Second Edition of ICD-O, where many of the terms were
ambiguous with respect to cell lineage. In the Third Edition,
the cell lineage is implicit in the four-digit morphology
code, and an additional (6th) digit is not required. However,
registries may wish to retain the additional digit to identify
cases in which the diagnosis is supported by immunophenotypic
data.
Cytogenetic Data
Cytogenetics and molecular biological data are now of key
- and increasing - importance in the diagnosis of many types
of hematologic malignancies. In ICD-O-3, an important change
has been the introduction of subcategories of acute myeloid
leukemia described according to cytogenetic abnormalities.
Where these abnormalities are included in a laboratory report,
they take precedence in classification over other data such
as the FAB morphology type.
|
