Quantitative response evaluation in acute myeloid leukemia (AML) and myelodysplastic syndromes (MDSs) relies on the morphologic quantification of bone marrow (BM) blasts. This process is subject to the operator-dependent quality of BM collection and the interobserver variability among pathologists.1???????-9 Determining responses can be further complicated by hemodiluted sampling, declined BM biopsies, dry taps, and confounding drug toxicities that prevent count recovery or give the impression of persistent dysplasia.
We previously observed that the clonal architecture of diagnostic BM samples in AML patients with leukocytosis is recapitulated in their simultaneously obtained peripheral blood (PB).10 Other groups have observed concordant PB NPM1 mutation clearance and PB copy number abnormalities11??-14 and have occasionally used PB for mutation discovery.15?-17 Therefore, we sought to compare the mutation burden in paired serial PB and BM samples in patients with AML or MDS to determine whether sequencing of PB samples is a viable approach for determining clonal architecture and whether it might provide an adjunct, and less invasive, measure of response to therapy.
We quantified mutation burden in PB vs BM samples in a subset of patients treated at Washington University with 10-day courses of decitabine (NCT01687400).18 Twenty-seven patients were selected: 22 with AML and 5 with MDS. Cases were selected based on the presence of at least 2 somatic mutations in the BM sample from each patient using a panel of 264 recurrently mutated AML genes (see supplemental Table 1, available on the Blood Web site) and adequate DNA from matched PB samples at multiple times. PB DNA was analyzed using this recurrently mutated AML gene panel (supplemental Methods; Welch et al18 and Cancer Genome Atlas Research Network19). In total, 138 somatic mutations were detected (median of 4 mutations per patient) across 93 time points (median of 3 time points per patient), providing a total of 446 pairwise comparisons of mutation detection in the blood vs marrow. The median white blood cell count across all time points was 1500/µL (range, 100-75?000/µL). The median age of the patients was 73 years (range, 47-88). Clinical responses included 5 complete remissions, 9 complete remissions with incomplete count recovery, 2 marrow complete remissions, 3 partial remissions, 6 stable disease, and 2 progressive disease. The median read depth in PB samples was ×193; in BM samples, the median read depth was ×295. All patients consented to genome sequencing analysis and were treated in accordance with the Declaration of Helsinki.
Mutation patterns observed in the PB strongly paralleled the BM results, including subclonal architecture (eg, 1012 and 1018), copy number variation (eg, 1038 and 1019), dynamic responses during decitabine therapy (eg, 1009 and 1048), early expansion of relapse subclones (eg, 1009 and 1021), and clonal hematopoiesis during remission unrelated to the malignant clone20 (eg, 1014) (Figure 1; supplemental Figures 1-4).