Macrophages and Mast Cells Infiltration Are Biomarkers of Primary Refractory Hodgkin's Lymphoma
Authors: Benedicte Deau , Emmanuel Bachy , Vincent Ribrag , Richard Delarue , Marie-Therese Rubio , Jacques Bosq , Viorel Vassiliu , Bruno Varet , Nicole Brousse , Olivier Hermine , Danielle Canioni 
Published: October 2019

Abstract
Abstract 3881
Classical Hodgkin's lymphoma is a highly curable lymphoma and about 80% of patients can be cured with modern treatment strategies. In spite of great clinical progress, a significant minority of classical Hodgkin's lymphoma experiences treatment failure after primary chemotherapy including a first line of anthracyclin-based regimen. Patients with refractory Hodgkin's lymphoma represent 5 to 10% of classical Hodgkin's Lymphoma. Many of these patients have a poor overall survival estimated at 25% at 5 years. A better biological characterization of such primary refractory patients might allow the use of early therapeutic intervention including targeted therapy. It remains, however, a challenge to identify patients whose disease will not be eradicated by standard therapy. Current prognostic models predict the outcome of treatment with imperfect accuracy, and clinically relevant biomarkers have not yet been established to improve the International Prognostic Score. For these reasons, reliable biomarkers for predicting long term survival at diagnosis are needed for such patients. Steidl et al. (Nejm,2010) recently reported the prognostic value of tumor-associated macrophages in patients with classical Hodgkin's lymphoma, showing that higher infiltration is associated with a shortened survival.
The value of tumor-associated macrophages in primary refractory Hodgkin's lymphomas has not been specifically assessed. In a retrospective study (Canioni et al., Plos one 2009), we previously evaluated 59 patients (18 with primary refractory or early relapse disease and 41 responders) collected from 1997 to 2004 in two hematology centres (Necker Hospital and Gustave Roussy Institute, Paris France) for c-kit expression by immunohistochemical analysis as a marker of mast cell infiltration and correlated the results with the response to treatment. All available poor prognosis patients were first identified (18 patients with primary refractory disease or early relapse (< 1year)) and the control group (47 responders) was randomly selected. Patients received conventional chemotherapy-based treatments [(MOPP (mechlorethamine, vincristine, procarbazine, and prednisone), ABVD (doxorubicine, bleomycine, vinblastine, and dacarbazine) or the combination of both or BEACOPP (bleomycine, etoposide, doxorubicine, cyclophosphamide, vincristine, procarbazine, prednisone)] and radiotherapy in stages I and II. Most patients presented a nodular sclerosis subtype of Hodgkin's lymphoma regardless whether they were refractory (17/18cases, 94.5%) or responders (37/41cases, 90%). In this cohort, 44 (75%) patients had a localized stage, whereas 19 (25%) had a disseminated disease. The results showed that refractory Hodgkin's lymphoma were associated with an excess of mast cells infiltration in the tumor cells microenvironment. The number of mast cells stained was significantly higher in refractory Hodgkin's lymphoma (c-kit+ mast cells > 6 per field) than in responders (c-kit+ mast cells ≤ 6) (p=0.001 and 0.0194 in univariate and multivariate analysis, respectively). In this cohort of patients, using CD68 staining we also found a statistically significant higher proportion of tumor-associated macrophages in refractory Hodgkin's lymphoma as compared to responders in univariate and multivariate analyses (p=0.0048 and p=0.0041, respectively). Therefore, we confirmed a strong correlation between the number of CD68 positive macrophages in the tumor stroma and clinical outcome. The use of such markers (CD68 and c-kit) in combination with well-established clinical risk factors could improve on the predictive value of a single biomarker used alone.
Therefore, in addition to mast cells, macrophages are also important players in refractory Hodgkin's lymphoma that may confer drug resistance to Hodgkin Reed Sternberg cells. Taken together, these data strongly suggest that microenvironment should be targeted in Hodgkin's lymphomas. In this regard, the use of kinase inhibitors that target both c-kit and M-CSF receptors could restore chemotherapy sensitivity in refractory Hodgkin's lymphoma and should be evaluated in clinical trials.

Disclosures:
No relevant conflicts of interest to declare.