Atypical patterns of primitive marker expression in acute myeloid leukaemia
From haematologyetc.co.uk
Table: Atypical marker patterns associated with specific AML subtypes
| While blast cells typically cause low side scatter of light and have an expression of CD45 that is lower than normal lymphocytes or monocytes, atypical pattterns may cause difficulty. These are often associated with particular AML subtypes. |
| AML with monocytic differentiation In AML with monocytic maturation those primitive cells with more mature monocytic features may show higher side scatter (consistent with their size and cytological features) and some or all of the blast cells may also have high expression of CD45 (comparable with normal or CMML monocytes). In such cases the neoplastic cells may lie in the typical monocyte area, and so are difficult to distinguish from reactive monocytes, or from typical or transforming CMML. It is important to compare with clinical and morphological features to ensure appropriate classification (click for further detail). |
| Acute promyelocytic leukaemia Cells of APL can vary in size and granularity an will often express a range of side scatter features may resemble those of maturing granulocytic cells, similarly CD45 expression may be similar to maturing granulocytic cells. The distribution of cells will be abnormal however and may variably include cells with wide range light scatter features that differ from those of typical blast cells. It is important to distinguish APL blasts from reactive myeloid cells or (in some cases) from cells of MDS. Morphological examination is essential, but consider also the pattern of additional markers (click for further detail). |
| Other patterns While most frequently blast cells with myeloid differentiation form a relatively homogenous group with moderately weak CD45 expression, in some cases very weak expression may be seen, or CD45 may have a broad width of expression. These patterns may more closely resemble the appearances of ALL or even of non-haematopoietic tumours. Stronger CD45 expression may also occasionally be seen. |