18F-FDG-PET/CT Imaging in Leukemia

FDG PET can be used for the assessment of CML patients. Nakajo et al., have reported2 cases of CML in the chronic phase that showed increased FDG uptake in the bone marrow in pretreatment period which got reduced in follow-up FDG PET scan in a patient after termination of treatment and in the other under treatment [11]. Varoglu et al., described a case of CML in a patient of renal cell carcinoma which showed increased FDG uptake in bone marrow prominent in the vertebral bodies, pelvic bones and proximal parts of the upper and lower extremities on FDG PET/CT imaging. It was suggested that FDG PET is useful in diagnosis and monitoring of chronic myeloid leukemia after treatment [12]. Extra-medullary blast proliferation may also be detected by FDG PET/CT in CML in patients revealing normal or CML in chronic phase morphology in peripheral blood smear/ bone marrow examination. So that local radiotherapy or change in systemic chemotherapy can be offered to the patients for appropriate management [19]. Falchi et al., suggested that FDG/PET is a useful diagnostic tool in patients with CLL and suspected Richter’s transformation. It can guide the site of biopsy for histologic confirmation of transformation. Patients with higher SUVmax are associated with worse clinical characteristics and worse prognosis. A SUV max>10 associated with inferior progression-free survival and overall survival in CLL patients [10]. In patients with different CLL phases, SUVmax reflects tumor aggressiveness. It was suggested that a SUV cutoff value equal or greater than 10 to diagnose the transformation of CLL into Richter syndrome [7-10]. Histologically aggressive CLL and Richter syndrome have higher SUV max and is associated with poorer performance status, lower hemoglobin and platelets, and higher lactate dehydrogenase and b-2-microglobulin [7].

There are few limitations of ¹⁸F- FDG PET-CT. FDG is not a very tumor-specific substance, in as much as the leukocytes and macrophages of inflammatory processes also accumulate the tracer which is a major source of false-positive diagnoses in the application of FDG-PET in oncology. Diffuse bone marrow uptake in FDG PET/CT may be due to an inflammatory reaction, recent chemotherapy or administration of hematopoietic growth factors/ colony stimulating factor. To reduce the potentially negative impact of occasional false-positive FDG-PET results on patient management, it is absolutely mandatory to carefully select the candidates for an FDG-PET scan to wait 8-10 weeks after surgery,10-12 weeks after local RT and 4-6 weeks after chemotherapy before an FDG PET scan is done.

To conclude, FDG PET/CT is useful in diagnosis and follow-up of patients with bone marrow malignancy.¹⁸F-FDG PET/CT may be useful for guiding the site of BM aspiration in cases with localized bone marrow involvement. It has an important role in diagnosing extra-medullary disease in de novo or relapsed AML patients. It can guide a diagnostic biopsy and may also provide prognostic information in patients with CLL. It is also useful in detection of Richter's transformation in CLL cases. Possibility of leukemia in known case of solid malignancies also kept in mind in follow up cases in which diffuse marrow uptake may be misinterpreted as chemotherapy effect or bone marrow metastasis by solid tumors. Bone marrow aspiration/biopsy must be performed for correct diagnosis and early management.