Clinical significance of the loss of CD20 antigen on tumor cells in patients with relapsed or refractory follicular lymphoma

Aim: Anti-CD20 monoclonal antibody is a cornerstone therapy for follicular lymphoma. Following anti-CD20 therapy, a potential decrease in CD20 antigen, and therefore a loss of the tumor target might be expected. However, the incidence and clinical significance of CD20 loss on tumor cells in patients with relapsed or refractory follicular lymphoma are unknown. This study aims to investigate the incidence and outcome of patients with relapsed or refractory follicular lymphoma patients harboring the loss of the tumor target, CD20. Methods: All consecutive adult patients with relapsed or refractory follicular lymphoma referred to the Early Drug Department at Gustave Roussy were included. The main objectives were to assess the incidence and prognosis of the loss in expression of CD20 antigen on the surface of tumor cells on patient outcome. Results: Over the study period 2013-2018, 131 patients were screened for clinical trials with B-cell malignancies in the early drug department of Gustave Roussy in France. Forty-four patients presented with relapsed or refractory follicular lymphoma and 32 had tumor biopsies at the time of relapse that were retained for analysis. The median (range) age was 67.5 years (55.3-75.3) and the median number of prior anti-cancer systemic therapies was 3 (2- 4). At the time of relapse, CD20 expression was positive in 84% of tumors (n = 27) and negative in 16% of tumors (n = 5). At a median follow-up of 18.3 (0.6-83.3) months, CD20 negativity was associated with a poorer prognosis with a median overall survival of 8.9 months (95%CI: 2.4-19.1) in comparison to CD20 positive patients (28.3 months, 95%CI: 25.1-75.3 months, P = 0.019). Conclusion: The loss of the tumor target antigen, CD20, occurred in 16% of patients with relapse or refractory follicular lymphoma. Due to confounding factors in patients who received anti-CD20 immunotherapy, it was not possible to formally establish the prognostic significance of CD20 negativity. However, we suggest that a check for CD20 antigen positivity nevertheless be performed to adapt subsequent therapies for patients with relapsed or refractory follicular lymphoma.