The white blood cell count at presentation is a key stratifier in acute promyelocytic leukemia. Patients with WBC at or below 10,000/ml are classified as low or intermediate risk, with a well-defined first-line induction approach supported by current evidence.
APL is risk-stratified by WBC count: above 10,000/ml is classified as high risk, while at or below this threshold — encompassing both low-risk and intermediate-risk patients — most clinicians today apply a unified first-line treatment strategy.
Induction in low/intermediate-risk APL is built around a combination of all-trans retinoic acid (ATRA) and arsenic trioxide (ATO), with concurrent attention to differentiation syndrome and coagulopathy — the full protocol provides the complete regimen.
The primary objectives are hematologic normalization and molecular clearance of PML-RARA by the end of induction, resolution of bleeding symptoms, and maintenance of fibrinogen above 100 mg/dL and platelet count above 30,000/ml.
In the era of ATRA, APL has been stratified into three categories of risk with regards to relapse-free survival (RFS): WBC >10,000/ml (high-risk), WBC ≤10,000 ml with platelet count ≤40,000/ml (intermediate-risk), and WBC ≤10,000/ml with platelet count >40,000/ml (low-risk).
Today, most clinicians will categorize APL within two categories, high risk (>10,000/ml) and low/intermediate risk.
In 2013, Lo-Coco et al. showed that combining ATO with ATRA in patients with non-high-risk APL led to an astounding 2-year DFS of 97% vs 86% in the ATRA plus idarubicin arm with less toxicity, again shifting the paradigm of APL treatment.
Rapid initiation of ATRA should begin at first suspicion of APL and should not be delayed for bone marrow aspiration or specialist consultation.
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