Marked Improvement in Staging Accuracy in Mycosis Fungoides/Sézary Syndrome Using Integrated Positron Emission Tomography and Computed Tomography (PET/CT).
Authors: Tsai Eunice Y. , Taur Alan , Espinosa Leandro , Quon Andrew , Dick Sarah E. , Chow Steve , Advani Ranjana , Warnke Roger A. , Kohler Sabine , Hoppe Richard T. , Kim Youn H. 
Published: October 2019

Staging of mycosis fungoides/Sézary syndrome (MF/SS), the most common cutaneous T cell lymphoma (CTCL), is primarily based on the type and extent of skin involvement and the presence or absence of extracutaneous disease. In patients with large cell transformation, tumors, erythroderma, or abnormal lymph nodes on physical exam, staging includes CT scan to look for visceral or lymph node (LN) disease followed by biopsy of enlarged LN. Integrated PET/CT combines anatomic data from CT with functional data from PET and has been useful in the staging of many non-Hodgkin’s lymphomas. To date, however, its role in staging MF/SS has not been investigated. We assessed the utility of integrated PET/CT in staging thirteen patients with MF (T2=1,T3=4,T4=1) or SS (T4B2=7) at high-risk for LN disease. Based on anatomic data from the CT component alone, only five of thirteen had enlarged LN (axillary/inguinal LN short axis ≥1.5cm or cervical LN short axis ≥1.0cm) and would have been referred for biopsy. In comparison, PET showed that all thirteen patients had hypermetabolic activity in at least one LN region. All patients had excisional LN biopsy and the extent of LN involvement was classified according to NCI criteria (LN1-4 classification). Six patients had LN1-3 and seven had effacement of LN architecture by lymphoma cells (LN4). Of the seven LN4 patients, four had SS and three had tumor MF. PET/CT helped identify the most suspicious LN region for biopsy, which led to the accurate stage of IVA. Notably, two patients had LN smaller than the CT size criteria and would have been incorrectly staged without the use of integrated PET/CT. Furthermore, we quantified the intensity of PET activity using standardized uptake value (SUV) and correlated this with LN grade. Patients with LN1-3 had a mean SUV of 2.7, median 2.2 (2.0–4.7) and patients with LN4 had a mean SUV of 5.4, median 3.9 (2.1– 11.8); p value 0.08. Ongoing analysis of additional patients may further define whether PET/CT can be used to significantly differentiate between LN1-3 vs LN4. Thus, for staging MF/SS, integrated PET/CT was more sensitive and specific in detecting malignant LN compared to CT alone and consequently provided more accurate staging and prognostic information. A larger scale study would be essential to confirm the superior staging capability of PET/CT over CT alone in MF/SS.

Summary of PET/CT correlation with LN pathology results in MF/SS

Patient T class Max SUV LN size (SA,cm) LN region NCI grade WHO grade Final stage Abbreviations: T, tumor; SUV, standardized uptake value; LN, lymph node; SA, short axis; cm, centimeter 1 T3 2.0 1.2 Axillary LN1 1 IIB 2 T4 2.1 1.3 Axillary LN1 1 IIIB 3 T2 2.2 1.0 Inguinal LN2 1 IIA 4 T4 4.7 1.0 Axillary LN2 1 IIIB 5 T4 3.0 1.2 Inguinal LN2 1 IIIB 6 T4 2.0 1.1 Inguinal LN3 2 IIIB 7 T3 3.7 1.4 Cervical LN4 3 IVA 8 T4 3.2 1.5 Inguinal LN4 3 IVA 9 T3 3.9 1.3 Inguinal LN4 3 IVA 10 T4 11.8 3.2 Inguinal LN4 3 IVA 11 T4 6.6 1.3 Inguinal LN4 3 IVA 12 T4 6.3 2.1 Inguinal LN4 3 IVA 13 T3 2.1 2.1 Axillary LN4 3 IVA