Utility of Positron Emission Tomography/Computed Tomography In Extranodal Natural Killer/T-Cell Lymphoma
Authors: Fujiwara Hideaki , Maeda Yoshinobu , Nawa Yuichiro , Yamakura Masayuki , Ennishi Daisuke , Miyazaki Yukihiro , Shinagawa Katsuji , Hara Masamichi , Tanimoto Mitsune , Matsue Kosei 
Published: October 2019

Abstract
Abstract 3101

Background:
Natural killer (NK/) T-cell lymphoma, nasal type, is an aggressive form of extranodal lymphoma that is common in Asia, but rare in Europe and North America. Although NK/T-cell lymphoma involves upper aerodigestive sites such as the nasal cavity and nasopharynx, it frequently involves other extranodal sites, including the gastrointestinal tract, bone marrow, adrenal gland, and skin. Because of the frequency of extranodal site involvement, pretreatment evaluation of disease extension is important for staging and treatment. Recently, 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) was evaluated for its usefulness in the prognosis and treatment response of aggressive B-cell lymphoma and Hodgkin's lymphoma, and relevant results were obtained. Many studies have evaluated the value of PET/CT for various types of B-cell lymphomas, but other similar studies involving T-cell and NK-cell lymphomas are rare. In the present study, we compared the utility of PET/CT and conventional modalities, particularly CT, in extranodal NK/T-cell lymphoma.

Patients and Method:
From January 2006 to April 2010, 19 untreated patients with extranodal NK/T-cell lymphoma (11 males and 8 females; median age 61 years; range 13–90 years) were included in the study. PET/CT and conventional procedures (e.g., CTs and biopsies) were compared and evaluated for their abilities to detect tumor lesions and their influence in staging and treatment strategies. PET/CT was performed as an initial staging procedure. In addition to PET/CT, all patients underwent initial staging workups, including whole-body CT with contrast media, biopsies from the bone marrow and other sites, and panendoscopies of the upper aerodigestive tract. Patients were evaluated for clinical stage by both evaluation modalities (PET/CT and conventional modalities) according to the Ann Arbor Staging System, and treatment strategies were first planned based on staging results. Following PET/CT, the clinical stage was reevaluated in each patient, and treatment strategies were decided based on the re-staging results.

Result:
Seven patients (37%) had bone marrow involvement, eight (42%) were in Ann Arbor stage I–II, and 11 (58%) had a systemic dissemination. Most patients with systemic dissemination (9/11, 82%) had cutaneous lesions. The median number of disease sites was 4 (range, 1–15). The median number of positive lesions was 3 (range, 1–15) by PET/CT compared to 2 (range, 0–14) by CT (p = 0.12). Using PET/CT, 108 lesions (93%) were detected, and at least one FDG-avid lesion was observed at initial staging workups in all patients. In contrast, 70 lesions (60%) were detected by CT, and three patients (16%) did not show any positive lesion. Two lesions (2%) at the nasal cavity that were detected by biopsy were undetectable by either PET/CT or CT. The nodal and extranodal regions were separately evaluated by PET/CT and conventional modalities. In total, 28 nodal lesions were detected: all (100%) were positive by PET/CT and 26 (93%) by CT. Conversely, 89 extranodal lesions were detected, and 83 (93%) and 44 (49%) were positive by PET/CT and CT (p = 0.003), respectively. For the detection of upper aerodigestive lesions, PET/CT and CT demonstrated similar results: 23 lesions (92%) vs. 17 (68%), respectively. Notably, PET/CT was superior to CT in detecting cutaneous lesions [31 lesions (100%) vs. 19 lesions (61%), respectively; p = 0.026]. Bone marrow involvement was confirmed pathologically in only seven patients; four cases (57%) were positive by PET/CT and none by CT. Using conventional modalities, 11 patients (58%) were in the localized stage and eight (42%) were in the advanced stage. Using PET/CT, eight (42%) were in stage I–II and 11 (58%) were in stage III–IV. Most patients received chemotherapy plus local irradiation in stage I–II, and intensive chemotherapy with or without hematopoietic stem cell transplantation in stage III–IV. One patient did not receive treatment because of unwillingness for treatment and older age. PET/CT findings altered the stage and treatment strategy in four (21%) and two cases (11%).

Conclusion:
In extranodal NK/T-cell lymphoma, PET/CT demonstrated a high detection rate for nodal and extranodal lesions, except in the bone marrow. PET/CT may have an impact on treatment strategy and is essential for risk-adapted treatment.

Disclosures:
No relevant conflicts of interest to declare.