PET-CT Scan for Detection of Extramedullary Acute Myeloid Leukemia

Acute myeloid leukemia (AML) at initial diagnosis or relapse may present with extramedullary (EM) AML. Data on the prevalence of EM AML at diagnosis are scarce and rely mostly on retrospective, clinical analyses. However, previous studies attributed EM AML as an impacting prognostic factor in AML. Furthermore, studies have not been carried out so far in order to define the prevalence and the prognostic impact of EM AML at diagnosis prior to initiation of therapy. ¹⁸Fluorodesoxy-Glucose Positron Emission Tomography (¹⁸FDG-PET) is able to detect highly metabolic tissue and has proven efficacy in imaging studies in various types of malignant diseases. The aim of this pilot study was to perform ¹⁸FDG-PET-CT scans on patients with newly diagnosed AML as well as relapsed AML in order to study its feasibility on detection of EM AML.

A total of 15 patients with AML (newly diagnosed AML, n = 10 and relapsed AML, n = 5) had total body ¹⁸FDG-PET-CT scans at diagnosis after giving informed consent to the study. Patients were included only if a delay of ≤ 5 days of initiation of induction- or re-induction chemotherapy was necessary to perform the study. ¹⁸FDG-PET-CT scans were performed using a Siemens Sensation 16 as part of a biograph with i.v. application of ¹⁸FDG (range of activity of 225 to 391 MBq).

A total of 15 patients with newly diagnosed or relapsed AML (age 26 to 80) underwent total body ¹⁸FDG-PET-CT imaging prior to initiation of induction- or re-induction therapy. Adverse reactions due to the application of i.v. ¹⁸FDG were not observed. A positive ¹⁸FDG-PET imaging result detecting an EM manifestation of AML was observed in 8 patients (53%). Sites of EM AML were soft tissue (n=7), mammary gland (n=1), liver (n=1), ovary (n=1), and lymph nodes (n=2). In 6 patients with clinically overt EM AML additional EM manifestations were detected. In 5 patients in whom there was no EM manifestation suspected, 2 had ¹⁸FDG-PET positive findings. Finally, most patients with positive ¹⁸FDG-PET uptake with either isolated EM or in combination with systemic AML relapsed within a short period of time after initiation of therapy or had a progressive disease despite therapy.

¹⁸FDG-PET-CT imaging is a useful tool in order to study EM AML either in combination or as a solitary event without fulfilling the criteria of systemic AML. ¹⁸FDG-PET is a feasible and safe imaging procedure and can therefore be performed prior to initiation of chemotherapy without a delay of time. ¹⁸FDG-PET might be a diagnostic tool in order to delineate the prevalence of EM AML and to define its impact to the prognosis of AML patients. Future studies to identify the prevalence and define the relevance of imaging studies in order to detect extramedullary AML are necessary.

Platzbecker: Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding.