Spatial heterogeneity and differential treatment response of acute myeloid leukemia and relapsed/refractory extramedullary disease after allogeneic hematopoietic cell transplantation

Abstract

Although extramedullary manifestations (EMs) are frequent in patients with acute myeloid leukemia (AML), they are often not detected during clinical workup and neither imaging- nor molecularly based diagnostic strategies are established to reveal their existence. Still, the detection of EM is essential for therapeutic decision-making, as EM present with aggressive and resistant disease and since mutational profiling might render patients within a different risk category, requiring personalized therapeutic strategies. Here, we report the case of an AML patient presenting with AML bone marrow (BM) infiltration and molecularly distinct EM at time of diagnosis followed by multiple EM relapses while undergoing several intensive chemotherapies including allogeneic hematopoietic cell transplantations (alloHCTs). ¹⁸Fluorodesoxy-glucose positron emission tomography (¹⁸FDG-PET)-imaging revealed EM sites in the mediastinum, duodenum, skin, and in retroperitoneal tissue, whereas recurrent BM biopsies showed continuous cytomorphologic and cytogenetic remission after alloHCT. To investigate the molecular background of the aggressive character of extramedullary disease and its differential treatment response, we performed amplicon-based next generation sequencing. An exon 4 (c.497_498insGA) frameshift RUNX1 mutation was exclusively found in all of the patient's EM sites, but not in the BM or in peripheral blood samples at time of EM reoccurrence. In addition, we detected an exon 13 (c.3306G>T) ASXL1 point mutation only in the retroperitoneal tumor tissue at the time of the fourth relapse. In contrast to the patient's intermediate-risk BM AML at diagnosis according to ELN2017, EM sites showed molecular adverse-risk features implicating intensified strategies like cellular therapies. Notably, disease relapse could only be detected by imaging throughout the course of disease. This case demonstrates both the necessity of continuous molecular profiling of EM to reveal differential molecular composition of EM and BM-derived AML, supposedly leading to divergent susceptibility to established therapies, as well as recurrent ¹⁸FDG-PET-imaging for detecting residual disease and assessment of treatment response in case of EM AML.

Keywords: AML; allogeneic stem cell transplantation; clonal landscape; extramedullary.

Figure 1.

Cytomorphology of bone marrow aspirates. (a) Bone marrow aspirate smear at time of diagnosis (50× magnification) showed subtotal infiltration of myeloid blasts replacing normal hematopoiesis without evidence of myeloid maturation, leading to diagnosis of acute myeloblastic leukemia without maturation according to WHO criteria. (b) Bone marrow aspirate smear at time of relapse (50× magnification) revealed persistence of cytomorphologic remission with a blast count below 5%, myeloid maturation, and normal findings for erythroid and megakaryocytic components. Bone marrow smears (a and b) were stained with the May–Grunwald–Giemsa kit and examined with the Nikon Eclipse E600 microscope. High-resolution pictures were taken with the mounted Nikon DSFi2 camera and processed with the Nikon Imaging Software Elements.

Figure 2.

Overview of the patient’s extramedullary AML sites. The patient suffered from multiple extramedullary relapses of different sites (1, mediastinal tumor; 2, duodenal tumor; 3, chloroma; 4, retroperitoneal tumor). The chronology of the occurrence of the EM was as follows: first diagnosis with mediastinal tumor (1), first relapse with duodenal tumor (2), second relapse with chloroma (3), and third relapse with retroperitoneal tumor (4). All EMs were (a) histologically confirmed after EM tissue was obtained by CT-supported biopsy (1 and 4), by duodenoscopy (2), or by punch biopsy (3). Histologic samples were prepared with hematoxylin–eosin staining. Images were captured with the Olympus BX 41TF microscope (magnification 1: 18.7×, 2: 40×, 3: 40×, and 4: 40×) and the 3DHistech Pannoramic Desk. (b) 18FDG-PET/CT imaging revealed mediastinal EM manifestation at diagnosis (b1), duodenoscopy pictured the duodenal tumor (b2), and follow-up 18FDG-PET/MRI depicted the retroperitoneal manifestation (b4). Figure was created with BioRender.

Figure 3.

Myeloid panel sequencing of EM, germline, and bone marrow samples. (a) Myeloid panel sequencing revealed recurrent RUNX1:c.497_498insGA frameshift mutation in exon 4 in all extramedullary sites, but not in the bone marrow aspirate or in germline DNA. (b) ASXL1:c.3306G>T point mutation in exon 13 was only detected in the retroperitoneal and latest EM site, while bone marrow, germline DNA, and other EM of the patient showed no ASXL1 aberration at previous AML disease stages.