Mid-Treatment Evaluation of 18-FDG-Positron Emission Tomography/Computed Tomography (PET) as Predictive Value of Response Assessment in Aggressive Non Hodgkin Lymphoma (NHL).

Introduction: The PET is mostly used in staging of NHL patients at diagnosis and as response assessment at the end of treatment. The evaluation by PET after few cycles of chemotherapy may be useful to predict chemosensitivity and then response, progression-free survival and overall survival in this subset of patients. In our study we introduced the PET in the mid-treatment evaluation (PET-2) of aggressive NHL disease.

Patients and methods: From June 2004 to December 2006, 25 consecutive aggressive NHL patients were evaluated for this study: 17 males and 8 females respectively with median age of 49 years (range 21–67). We included: 18 Diffuse Large B Cell, 1 anaplastic, 2 mantle cell, and 4 follicular grade III NHL. Patients characteristics were: 11/25 bulky disease; 20/25 intermediate or high IPI risk; 3/25 stage II, 3/25 stage III and 19/25 stage IV. All patients were staged according to standard imaging procedures completed by PET at the diagnosis and at the end of treatment. After 2 or 4 cycles of Rituximab-CHOP-like chemotherapy PET-2 was repeated in all of them.

Results: PET-2 demonstrated: 16/25 patients negative and 9/25 patients positive. The conventional and PET restaging performed at the end of treatment were 21/25 negative and 4/25 positive. Among the 16 patients PET-2 negative, 14/16 remained negative at the final PET evaluation and achieved CR, 2/16 became positive with demonstration of progression disease. Among the 9 patients PET-2 positive, 7/9 became negative with achievement of CR. The other 2/9 patients remained positive at the end of therapy: one of them was false positive because of parotid gland carcinoma without NHL involvement. Among 21/25 patients PET negative at the final evaluation, 20/25 patients remained in CR with a median follow-up of 18 months and only one patient negative at the PET-2 and at the final PET demonstrated disease progression. Finally, with a median follow-up of 18 months, FFS was 84% in all pts, 81% in PET-2 negative patients and 89% in PET-2 positive patients respectively.

Conclusions: The PET is an important imaging technique for staging and end-treatment evaluation in lymphoma disease, because it can better define CR patients. In Hodgkin disease several studies demonstrated that the early evaluation by PET is a crucial prognostic factor to test chemosensitivity and then to predict favourable outcome. In our study the mid-evaluation of response by this procedure had not so clear predictive value of response assessment, because patients, even if positive at PET-2, can achieve CR at the end of treatment. More large studies are needed to determine the real impact of on-course PET as response assessment in aggressive NHL patients.