FDG-PET Scans as a Staging Study for T-Cell Lymphomas: High Rates of Positivity Do Not Result in Frequent Changes in Stage.
Authors: Horwitz Steven M. , Foss Francine , Goldfarb Shari , Molina Ana , Hamlin Paul A. , O’Connor Owen A. , Cammarata Michelle , Moskowitz Craig H. , Zelenetz Andrew D. 
Published: October 2019

Abstract
FDG-PET is emerging as a standard staging study for diffuse large B-cell lymphoma and Hodgkin’s disease. There is little experience with PET in staging T-cell lymphomas (TCL). TCL often involve extranodal sites not well imaged by standard CT. We hypothesized that PET would add to staging by detecting additional sites of disease. To address this question we reviewed our TCL database to identify patients (pt) who had PET as part of complete staging at initial diagnosis or at relapse. Each pt was included once. Staging included physical exam, CT scan of the chest/abdomen/pelvis alone or as part of a PET/CT combination, and bone marrow (BM) biopsy. Studies such as MRI of the sinus or ultrasound of the testes were done as clinically indicated. We reviewed 107 pt who met the above criteria. Histologies were as follows: peripheral T-cell lymphoma NOS (PTCL), angioimmunoblastic T-cell lymphoma (AILT), anaplastic large cell lymphoma, ALK-1-, (ALCL−), anaplastic large cell lymphoma, ALK-1+, (ALCL+), mycosis fungoides (MF), subcutaneous panniculitis-like T-cell lymphoma (SPTCL), adult T-cell lymphoma (ATL), NK lymphoma nasal type (NK-Nas), lymphoblastic lymphoma (LL), enteropathy associated T-cell lymphoma (EATCL), blastic NK lymphoma (BLNK), primary cutaneous ALCL (ALCL-Cut), and hepatosplenic T-cell lymphoma (HSPTCL). All pt with MF had suspicion of extracutaneous disease. Overall 95/107 (89%) had a PET interpreted as positive by visual review. Standard uptake values (SUV) varied from 1.1–20.5 g/ml. Of the 12 pt with negative PET scans, 7(58%) had no evidence of disease on CT including PTCL (n=3, stage I resected), HSPTCL (n=2, liver, spleen, BM disease only), ALCL-Cut (n=2, skin only).
T-cell Lymphoma-PET Results Histology N PET + % positive SUV Range (g/ml) ALL PT 107 95 89% 1.1–20.5 PTCL 27 24 88% 2–20 AILT 19 16 84% 2–11.7 ALCL− 12 12 100% 3–19.6 ALCL+ 4 4 100% 4–12 MF 12 10 83% 1.8–17.6 SPTCL 8 8 100% 1.4–13.1 ATL 5 5 100% 2.9–19.7 NK-Nas 5 5 100% 3.4–13.1 LL 3 3 100% 5.5–20.5 EATCL 3 3 100% 3.5–9.9 ALCL-Cut 5 3 60% 1.1–1.4 BLNK 2 2 100% 1.929.5 HSPTCL 2 0 0 N/A
PET detected additional sites of disease in 34/107 (32%). These sites detected by PET were skin/subcut (n=9), bone (n=7), lymph node (n=6), spleen (n=3), nasopharynx/sinus (n=2), liver (n=2), BM (n=1), bowel (n=1), muscle (n=1), kidney (n=1), tonsil (n=1), testes (n=1). Three new malignancies were incidentally detected by PET including lung cancer (n=1), metastatic renal cell to the parotid (n=1), and mantle cell lymphoma (n=1 in a pt with ALCL-cut). Despite these additional sites, stage was changed in only 10/107 (9%). We did not use negative PET to downstage. Sites resulting in higher stage included bone (n=3), lymph node (n=2), subcut/muscle (n=3), testes (n=1), liver (n=1). Skin lesions were noted on physical exam and therefore did not change stage. In conclusion, TCL are almost universally PET positive. PET often adds information by identifying extranodal disease. However, partly due to many pt being stage IV by other modalities, PET resulted in a change of stage in <10% of pt. PET may be particularly useful in assessing of skin sites. These data suggest that it may be beneficial to include PET in the response assessment of TCL, as has been proposed for DLBCL and HL in revised NHL response criteria.