Role of Positron Emission Tomography Imaging in Myeloid Sarcoma

Sir,

We read with great pleasure the recent article wrote by Chandra et al. on “Role of positron emission tomography/computed tomography (PET/CT) scan in acute myeloid leukemia (AML).”[1] Myeloid sarcoma (MS) is a challenging entity for both diagnosis and treatment. Literature provides very limited information about MS diagnosis and treatment, and hence, oncologists all over the world follow their institution-formulated approach.

Tissue biopsy is considered as a gold standard for any pathological mass. However, in certain cases, where location or size of mass prevents from getting adequate specimen, treatment depends on other leading clues provided by advanced diagnostic tools. PET/CT imaging has proven to be an important asset in the management of solid hematological malignancies such as lymphomas and extramedullary plasmacytomas.[2] However, unfortunately, diagnosis and follow-up for liquid malignancies such as acute leukemias rely mostly on bone marrow examination and flow cytometry. Although minimal residual analysis has revolutionized the field of diagnosis and management in case of leukemia to some extent, we still lag behind in managing special subsets of leukemia such as MS. The stormy course of AML, high prevalence of opportunistic infections, intense chemotherapy, and use of granulocyte colony-stimulating factor (G-CSF) are few of the factors causing false-positive readings while analyzing PET/CT scan. Similar to Chandra et al., Stölzel et al. in his report of 10 AML patients had similar findings with detection of occult granulocytic sarcoma in 60% of cases.[3] This suggests that PET/CT imaging certainly helps to know the exact tumor burden in an individual thereby helpful in proper counselling and better formulating a more intense chemo regimen.

In some cases, the histopathological specimen is difficult to retrieve from inoperable sites. A recent review on the role of PET/CT imaging on cardiac MS has justified its pivotal role.[4] PET/CT has made possible image-guided biopsy from the most suitable site with highest standardized uptake value, thereby increasing the possibility to get the most appropriate sample. During follow-up, as many patients express their unwillingness for bone marrow punctures, PET/CT may prove to be a pivotal substitute in such cases.

Cost factor, insurance coverage, and false-positive rates (due to chemotherapy, G-CSF, and infections) are few relevant obstacles which still need to be addressed before any fixed guidelines could be laid down. In the era of molecular assessment, in which remission is evaluated with documentation of the status of minimal residual disease in an AML case, it would be interesting to witness to how much extent PET/CT would be able to establish its role.

At present, we recommend the judicial use of PET/CT in selected cases to improvise patient management. Well-designed prospective trial will certainly answer the queries related to timings of PET/CT scan assessment, target cases, measures to tackle the confounding factors, and it's role during follow-up.