Early prediction of response to therapy: the clinical implications in Hodgkin’s and non-Hodgkin’s lymphoma

Interim FDG-PET in Hodgkin lymphoma: a compass for a safe navigation in clinical trials?

Despite the rewarding results achieved in the treatment of Hodgkin lymphoma (HL), concerns have been raised regarding the long-term complications induced by therapy. Hence, the current challenge is to develop a new therapeutic strategy maintaining excellent patient outcome while reducing potentially life-threatening late adverse effects. Therefore, it would be beneficial to identify chemoresistant or refractory patients early during therapy for appropriate and timely escalation of treatment. Recently, compelling data have emerged on the prognostic role of interim [18F]-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) performed early during the course of treatment to predict ultimate outcome, even proving superior to conventional prognostic factors. Several ongoing prospective trials are exploring the feasibility of treatment de-escalation strategies in patients with a negative interim PET, as well as therapy escalation in advanced-stage HL patients who have a positive interim PET result. In this article, the published reports on the contribution of interim PET to the design of ongoing response-adapted clinical trials are reviewed. Moreover, some of the unresolved issues revolving around the suboptimal positive predictive value of interim PET are addressed with an emphasis on the interpretation criteria. A final remark on the appropriate use of interim PET is also provided.

Interim positron emission tomography scan in Hodgkin lymphoma: definitions, interpretation rules, and clinical validation

[18F]-Fluoro-2-deoxy-d-glucose positron emission tomography (18F-FDG PET) scan performed early during the therapy for Hodgkin lymphoma (HL) has a high prognostic value and correlates with survival. Several ongoing trials are under way to investigate the value of treatment adaptation based on early 18F-FDG PET results both in early and advanced-stage HL. In the former, in order to reduce the number of patients in whom involved-field radiotherapy is required for optimal treatment, and in the latter to identify the small subset (about 20%) of patients with a dismal prognosis who should be treated very aggressively while sparing the toxic effects of the therapy in most of them. However some issues still remain unsettled, including the standardization of interpretation rules for the interim-positron emission tomography (PET) scan, the optimal time to perform this examination during therapy, and the impact of a risk-adapted therapeutic strategy on the overall outcome of therapy in HL. International efforts are now underway to reach a consensus among experts on a set of simple, reproducible rules for PET interpretation, and attempts are being made to launch retrospective clinical studies so as to validate these rules.

Report on the First International Workshop on Interim-PET-Scan in Lymphoma

An international workshop, under the auspices of Group d'Etude des Lymphomes de l'Adulte (GELA) took place in Deauville, France, in April 3-4, 2009. The European experts with a published or personal experience on interim-PET in lymphoma were invited to the meeting. The aim of the workshop was twofold: (1) to reach a consensus on simple, reproducible criteria for interim-PET interpretation in Hodgkin lymphoma and diffuse large B-cell lymphoma (DLBCL), and (2) to launch two or more international validation studies, in an attempt to validate these rules. We concisely report here the minutes of the meeting and the conclusions/statements that have been reached.

Bone marrow involvement in diffuse large B-cell lymphoma: correlation between FDG-PET uptake and type of cellular infiltrate

PURPOSE

To assess, in patients with diffuse large B-cell lymphoma (DLBCL), whether the low sensitivity of (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) for bone marrow assessment may be explained by histological characteristics of the cellular infiltrate.

METHODS

From a prospective cohort of 110 patients with newly diagnosed aggressive lymphoma, 21 patients with DLBCL had bone marrow involvement. Pretherapeutic FDG-PET images were interpreted visually and semiquantitatively, then correlated with the type of cellular infiltrate and known prognostic factors.

RESULTS

Of these 21 patients, 7 (33%) had lymphoid infiltrates with a prominent component of large transformed lymphoid cells (concordant bone marrow involvement, CBMI) and 14 (67%) had lymphoid infiltrates composed of small cells (discordant bone marrow involvement, DBMI). Only 10 patients (48%) had abnormal bone marrow FDG uptake, 6 of the 7 with CBMI and 4 of the 14 with DBMI. Therefore, FDG-PET positivity in the bone marrow was significantly associated with CBMI, while FDG-PET negativity was associated with DBMI (Fisher's exact test, p=0.024). There were no significant differences in gender, age and overall survival between patients with CBMI and DBMI, while the international prognostic index was significantly higher in patients with CBMI.

CONCLUSION

Our study suggests that in patients with DLBCL with bone marrow involvement bone marrow FDG uptake depends on two types of infiltrate, comprising small (DBMI) or large (CBMI) cells. This may explain the apparent low sensitivity of FDG-PET previously reported for detecting bone marrow involvement.