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AML Blast Clearance

A study published in Blood (2007;110:4172-4174) showed that, as in childhood acute lymphoblastic leukemia (ALL), the time to clearance of circulating blasts from peripheral blood also serves as an independent prognostic marker of relapse-free survival (RFS) and overall survival (OS) for acute myeloid leukemia (AML).

In an effort to evaluate the impact of time to peripheral blood blast (PBB) clearance on RFS and OS, researchers from the Mayo Clinic and Northwestern University retrospectively analyzed a cohort of 86 adult patients with AML (excluding acute promyelocytic leukemia) who received uniform induction and consolidation chemotherapy. Patients with PBBs at initiation of induction chemotherapy (n = 73) were separated into 2 groups based on whether blasts were cleared on or before day 5 (n = 45) or after day 5 (n = 28). Significant differences were observed with regard to different rates of relapse of 33% and 79% between the day 0 to 5 and day 6 or later subgroups, respectively. Significant differences in OS were also noted between these 2 subgroups.

The researchers also divided patients into 3 “blast risk groups” (good, intermediate, and poor) based on blast clearance on or before day 3, days 4 to 5, or day 6 or later. The good, intermediate, and poor risk groups had significantly different relapse rates of 12.5%, 47%, and 78%, respectively.

Univariate analysis of multiple variables at the time of diagnosis showed that only the day to blast clearance, number of induction cycles and the cytogenetic risk group had a significant impact on RFS. Multivariable analysis of these 3 variables showed that only the day of blast clearance or "blast-risk group" was an independent prognostic marker of RFS. Similar findings were noted with univariate analysis for OS in which only "blast-risk group" and number of induction cycles to achieve complete remission significantly impacted prognosis.

This study’s findings demonstrated that in AML patients achieving complete remission following standard chemotherapy, the time to PBB clearance had the strongest independent prognostic impact on RFS and OS. Additionally, the authors concluded that the time to PBB clearance, in acting as an early marker of in vivo chemosensitivity, potentially serves as a valuable measure of treatment response in AML patients.

At most hospital laboratories the time to PBB clearance can be determined by a daily complete blood count (CBC) with a differential count, which is routinely performed on an automated analyzer in the hematology laboratory. Manual slide differential counts of one hundred cells are performed in all cases which are flagged by the analyzer due to immature granulocytes, including circulating blasts.

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