The Predictive Value of PET/CT for Post-Transplant Outcomes in T Cell Lymphoma

Objective

¹⁸F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) is used routinely for response assessment and treatment decision making in Hodgkin lymphoma and B cell non-Hodgkin lymphoma. The predictive value of PET/CT in patients with peripheral T-cell lymphomas (PTCL) is not well defined. We performed a retrospective single institution analysis to determine the utility of pre-transplant PET/CT to predict outcomes following autologous stem cell transplant (ASCT) for PTCL.

Materials and Methods

PET/CT patient population

We screened the Dana-Farber Cancer Institute database for patients undergoing ASCT between 2005 and 2015 and identified 109 PTCL patients. Patients had PET/CT performed within 3 months prior to transplant and follow up PET/CT within one year of ASCT. 38 patients met the inclusion criteria (17 women, 21 men, mean age at transplant 56 years, SD ±14.6, range 22-73).

Image interpretation

The FDG-PET/CT images were reviewed on HERMES GOLD (Hermes Medical Solutions AB, Stockholm, Sweden) workstation by a radiologist (AON) blinded to clinical details. Pre-transplant PET/CT images were read initially and then one week later the post-transplant PET/CT images were read with the reader blinded to the pre-transplant PET/CT findings. The Deauville five-point scale was used for staging and assessment of treatment response and recurrence. A Deauville score of 3 or less was considered a complete response (CR).

Results

There was mean of 1.3 months between the initial PET/CT and transplant. Mean of 5 months between transplant and follow up PET/CT.

A total of 30 patients had a CR on pre-transplant PET/CT. There were 8 patients with persistent sites of FDG uptake on PET/CT with Deauville 4 (n=4), Deauville 5 (n=2) consistent with partial response to treatment. Pre-transplant PET/CT did not correlate with long term survival outcomes including 3-year PFS in our data; a negative pre-transplant PET/CT was not associated with improved 3-year PFS as compared to a positive pre-transplant PET/CT.

A total of 26 patients (68%) had no evidence of disease on post-transplant PET or negative post treatment PET/CT. Of those, 23 (88%) had a 3 -year progression free survival, 13 (50%) had a 5-year progression free survival, and 5 (19%) had died of recurrent disease at the time of our analysis.

On post-transplant, a total of 12 patients had positive PET/CT with 6 achieving partial remission and 6 having progressive disease on post-transplant PET/CT. In terms of outcome, the 3-year PFS for the PET positive group was 42% (5/12). Of those, 2 (17%) had durable 5-year PFS with treatment after transplant while the other 10 (83%) eventually died of their disease.

The 3-year PFS rate in the PET negative group was 88% (23/26) (95% CI: 70 - 98%) and 42% (5/12) (95% CI: 15 - 72%%) for PET positive group. The difference in the 3-year PFS in the PET negative group is significantly larger than that of the PET negative group (p<0.005). The 5-year PFS in the PET negative group was 50% (13/26) and 17% (2/12) for the PET positive group with a marginally significant difference (p=0.08)

Conclusions:

Patients with a negative post-transplant PET/CT had a 3-year PFS of 88% and 5-year PFS of 50% compared to a 3-year PFS of 42% and a 5-year PFS of 17% in patients with a positive post-transplant PET/CT. This suggests that post-transplant PET/CT is a clinically meaningful predictor of long-term disease-free survival. The PFS data in the patients with a negative post-transplant PET/CT compares favorably to that of patients not stratified by PET/CT in prospective trials including a 5-year PFS of 44% in the NLG-T-01 study which looked at 115 PTCL patients who underwent ASCT in the up-front setting (d'Amore F, et al. J Clin Oncol. 2012 Sep 1;30(25):3093-9). Our findings that negative pre-transplant PET/CT are not predictive of survival or associated with an improved 3-year PFS in comparison to positive pre-transplant PET/CT was in keeping with the findings of another retrospective analysis of 48 patients, which compared the 3-year PFS and OS of patients with positive and negative pre-transplant PET/CT studies (Shea L, et al. Leuk Lymphoma. 2015 January; 56(1): 256-259).