Table 6. Proposed classification and criteria of basophilic leukemiasa .
| Disease variant | Proposed criteria |
|---|---|
| ABL | Myeloblasts+metachromatic blasts ⩾ 20% and basophilsb ⩾ 40% of nucleated BM or PB cells (and HB criteria are fulfilled) |
| Primary ABL | - No preceding or underlying BM neoplasm |
| Secondary ABLc | - Known preceding/underlying BM neoplasmd |
| CBL | Myeloblasts+metachromatic blasts < 20% and basophils ⩾40% of nucleated BM or PB cells (and HB criteria are fulfilled) |
| Primary CBL | - No preceding or underlying BM neoplasm |
| Secondary CBLc | - Known preceding/underlying BM neoplasmd |
Abbreviations: ABL, acute basophilic leukemia; BM, bone marrow; CBL, chronic basophilic leukemia; HB, hyperbasophilia; PB, peripheral blood; WHO, World Health Organization.
The diagnosis basophilic leukemia (ABL or CBL) is established on the basis of the criteria shown in this table, investigations proposed in Table 4, and exclusion of reactive HB. A diagnostic algorithm is shown in Supplementary Figure S2.
In ABL, many or even most of the basophils may be quite immature cells. When all these cells are metachromatic blasts, they can only be regarded (counted) as ‘basophils’ when the basophil lineage has been confirmed by immunophenotyping or electron microscopy.
Secondary BL variants should be further sub-classified according to the type of preceding or underlying BM neoplasm—these neoplasms should be classified according to the WHO proposal.
The presence of the Ph-chromosome or BCR-ABL1 p210 counts as a definitive sign of an underlying BM neoplasm even if no known prephase of overt CML had been diagnosed before. In these patients, the treatment plan also needs to be adjusted according to the detection of BCR-ABL1.