PB1815 CLINICAL IMPLICATIONS OF T CELL RECEPTOR (TCR) GENE REARRANGEMENT, 18F‐FDG‐PET/CT AND UNILATERAL BONE MARROW TREPHINATION FOR DETECTING BONE MARROW INVOLVEMENT IN PERIPHERAL T CELL LYMPHOMAS

Abstract

Background:Bone marrow involvement (BMI) is an important prognostic factor for the treatment of peripheral T‐cell lymphomas (PTCLs). The trephining of bone from the iliac crest is the most generally accepted diagnostic approach to evaluate BMI to date. However, iliac bone trephination has some limitations such as low sensitivity owing to patch or focal lymphomatous involvement, problems of procedure technique and diversity according to the inspectors.Aims:So, we investigated that whether the combined evaluation with 18F‐FDG PET/CT and molecular analysis of T‐cell receptor (TCR) gene rearrangement could increase the prognostic information of BMI at the time of diagnosis in PTCLs.Methods:This study conducted prospectively in 46 patients with newly diagnosed PTCL from April 2017 to January 2019. Three patients were excluded due to the lack of baseline 18F‐FDG PET/CT and 4 patients were excluded due to the diagnostic pathology of anaplastic lymphoma kinase (ALK)‐positive anaplastic large cell lymphoma and indolent cutaneous T‐cell lymphomas. Finally, 39 patients were investigated based on three parameters at diagnosis. The specimens for TCR gene rearrangement polymerase chain reaction (PCR) to detect the clonality were obtained by fine‐needle aspiration and unilateral iliac trephination biopsy.Results:Fifteen (37.5%) patients were diagnosed with NK/T cell lymphoma, 11 (27.5%) with angioimmunoblastic T cell lymphoma (AITL), 7 (17.5%) with peripheral T cell lymphoma, not otherwise specified (PTCL‐NOS), 3 (7.5%) with ALK negative anaplastic large cell lymphoma and 3 (7.5%) with enteropathy‐associated T cell lymphoma. Twenty‐three (59.0%) patients showed advanced stage and 9 (22.5%) patients were confirmed morphologic bone marrow involvement (mBMI) by trephination biopsy. TCR gene rearrangement (TCR BMI) was detected in 29 (72.5%) patients and bony involvement on 18F‐FDG PET/CT assessment (PET BMI) was detected in 8 (20.0%) patients. Seven out of 9 patients with mBMI were concordant with TCR BMI, however, only two patients with mBMI showed the positivity in FDG PET/CT.Overall diagnostic accuracy of TCR BMI for detection of conventional mBMI was calculated with sensitivity of 77.8%, specificity of 26.7%, positive predictive value (PPV) of 24.1% and negative predictive value (NPV) of 80.0%, respectively. Five patients were detected to have the positivity in both TCR rearrangement and FDG PET/CT but no bone marrow involvement in morphologic trephination. The median progression‐free survival (PFS) of these patients was as poor as those with mBMI (6.93 months vs. 13.33 months, P = 0.250).Summary/Conclusion:Althouth both FDG PET/CT and TCR gene rearrangement PCR have low relevance to conventional mBMI, the combined evaluation with FDG PET/CT and TCR gene rearrangement could be useful to predict bone marrow microinvolvement and poor prognosis.