Accelerated-phase CML: de novo and transformed

Despite the dramatic improvements in outcomes for the majority of chronic myeloid leukemia (CML) patients over the past 2 decades, a similar improvement has not been observed in the more advanced stages of the disease. Blast phase CML (BP-CML), although infrequent, remains poorly understood and inadequately treated. Consequently, the key initial goal of therapy in a newly diagnosed patient with chronic phase CML continues to be prevention of disease progression. Advances in genomic investigation in CML, specifically related to BP-CML, clearly demonstrate we have only scratched the surface in our understanding of the disease biology, a prerequisite to devising more targeted and effective therapeutic approaches to prevention and treatment. Importantly, the introduction of the concept of "CML-like" acute lymphoblastic leukemia (ALL) has the potential to simplify the differentiation between BCR::ABL1-positive ALL from de novo lymphoid BP-CML, optimizing monitoring and therapeutics. The development of novel treatment strategies such as the MATCHPOINT approach for BP-CML, utilizing combination chemotherapy with fludarabine, cytarabine, and idarubicin in addition to dose-modified ponatinib, may also be an important step in improving treatment outcomes. However, identifying patients who are high risk of transformation remains a challenge, and the recent 2022 updates to the international guidelines may add further confusion to this area. Further work is required to clarify the identification and treatment strategy for the patients who require a more aggressive approach than standard chronic phase CML management.

Abnormal B-lymphoblasts in myelodysplastic syndromes and myeloproliferative neoplasms other than chronic myeloid leukemia

BACKGROUND

Lineage infidelity is characteristic of mixed phenotype acute leukemia and is also seen in blast phase of chronic myeloid leukemia (CML), myeloid/lymphoid neoplasia with eosinophilia and gene rearrangements, and subtypes of acute myeloid leukemia. Driver genetic events often occur in multipotent progenitor cells in myeloid neoplasms, suggesting that multilineage output may be more common than appreciated. This phenomenon is not well studied in myelodysplastic syndrome (MDS) and non-CML myeloproliferative neoplasms (MPN).

METHODS

We systematically evaluated phenotypic lineage infidelity by reviewing bone marrow pathology and flow cytometry (FC) studies of 1262 consecutive patients with a diagnosis of MDS and/or non-CML MPN. We assessed B- and T-cells in these patients by FC. When abnormal B-lymphoblast (ABLB) populations were detected, we additionally evaluated immature B-cells using a high sensitivity FC assay for B-lymphoblastic leukemia/lymphoma (B-ALL).

RESULTS

We identified 9 patients (7 MDS, 7/713, 1%; 2 non-CML MPN, 2/312, 0.6%; 0 in MDS/MPN) with low-level ABLB populations (0.012%-3.6% of WBCs in marrow) with abnormal immunophenotypes. Genetic studies on flow sorted cell populations confirmed that some ABLB populations were clonally related to myeloid blasts (4/6, 67%). On follow-up, ABLB populations in 8/9 patients remained stable or disappeared. Only 1 case progressed to B-ALL.

CONCLUSIONS

These findings demonstrate that phenotypically detectable abnormal immature B lineage output occurs in MDS and non-CML MPN, albeit rarely. While presence of ABLB does not necessarily reflect blast crisis, the underlying disease biology of our findings may ultimately be relevant to patient management and warrants further investigation.

Incidence and immunophenotype of abnormal lymphoblast populations at diagnosis of chronic myeloid leukaemia in chronic phase

Chronic myeloid leukaemia most commonly presents in chronic phase (CML-CP) and it is characterised by granulocytic proliferation. Many patients have an excellent response to tyrosine kinase inhibitor therapy; however, a small proportion will develop lymphoid or myeloid blast crisis, with inferior clinical outcomes. Detection of lymphoblasts at diagnosis of CML-CP has been reported in small case series with conflicting results on the risk of subsequent blast crisis. The aim of this study was to identify the incidence and immunophenotype of abnormal lymphoblast populations in CML-CP. Retrospective review of bone marrow flow cytometry results of consecutive patients with newly diagnosed CML-CP between June 2012 and February 2021 was performed. Lymphoblasts, myeloblasts, haematogones, and mature lymphocytes were evaluated. Fifty-nine patients had bone marrow flow cytometry results available for review. Abnormal lymphoblast populations were detected in four patients (7%) comprising 0.05–0.19% of bone marrow events. The immunophenotype was similar but distinct from haematogones. The most common distinguishing features of the abnormal lymphoblast populations were abnormally bright expression of CD19 or CD10, weak CD38 or aberrant CD20 expression on CD34 + cells. The clinical case of one of the patients with abnormal lymphoblasts detected at diagnosis who went on to subsequent blast crisis is discussed. Abnormal lymphoblasts can be identified in CML-CP and may be under-recognised. Their detection requires careful analysis in order to distinguish them from normal precursors. The clinical significance of such populations requires further study.

Sudden blast phase in pediatric chronic myeloid leukemia-chronic phase with abnormal lymphoid blasts detected by flow cytometry at diagnosis: Can it be considered a warning sign?

BACKGROUND

Inconclusive knowledge persists regarding the course of chronic myeloid leukemia-chronic phase (CML-CP) patients with detectable abnormal blasts by flow-cytometry at diagnosis. The 2016 WHO classification is not specific regarding sub-classification of CML with <10% abnormal B-lymphoid blasts (ABLB), and suggests these patients often show rapid progression. We report the clinical course of pediatric CML-CP patients who had detectable abnormal blasts by flow-cytometry at baseline.

METHODS

Retrospective audit of all pediatric CML patients between January 2013 and December 2017 were included. Their clinical presentation, demographic profile, and treatment outcomes were extracted from electronic medical records. Some of these patients got flow-cytometry done by default, though it was not a routine part of diagnostic CML marrow studies.

RESULTS

Amongst 65 pediatric CML patients, flow-cytometry at initial diagnosis was available in 15 (CP-12; AP-3). Of the 12 CML-CP patients, 10 (83%) had abnormal flow-cytometric findings-5 (50%) with mixed lineage blasts (4-B/Myeloid, 1-B/T/Myeloid), and myeloid lineage blasts in the remaining 5 (50%). At a median follow-up of 26 months (range: 9-34 months), 3/5 patients with ABLB at diagnosis progressed to frank blast crisis (2 B-cell; 1 Mixed lineage). None among the five patients with diagnostic myeloid-alone aberrant blasts progressed to blast crisis. Imatinib resistant mutation was also found in 3/5 (60%) CML-CP patients with these ABLB at baseline.

CONCLUSIONS

Although a retrospective study with limited sample size, presence of ABLB detected on flow-cytometry in CML-CP patients, had a noticeable early conversion to CML-BC in our cohort. Incorporation of flow-cytometry in diagnostic work-up can provide useful insight regarding the behavior of pediatric CML-CP patients and guide therapy.