Comparison of Tumor Lysis Syndrome (TLS) Risk Reduction and Incidence in Different Venetoclax-Based Combinations within the Randomized Phase 3 GAIA (CLL13) Trial

Background: In early studies of venetoclax (ven) in CLL, severe tumor lysis syndromes (TLS) were observed leading to the implementation of multiple safety measures including a 5-week ramp up schedule. Since then, studies have consistently reported low rates of TLS in ven-treated patients (pts), most likely as a result of strict prophylactic and laboratory monitoring measures. Various lead-in regimens prior to the administration of ven were shown to be feasible and effective in reducing the risk of TLS in pts with CLL. However, no comparison of different pretreatment regimens has been performed so far in a prospective randomized trial. Using the set-up of the GAIA trial, we compared TLS incidence and formal TLS risk reduction between 3 different ven-based combinations. Methods: The phase 3 GAIA (CLL13) trial compared 3 different time-limited ven-based combinations against standard chemoimmunotherapy (CIT) in fit, treatment-naïve pts with CLL. Pts were randomized to receive CIT (FCR in pts ≤65 years; BR in pts >65 years), ven and rituximab (RVe), ven and obinutuzumab (GVe), or ven, obinutuzumab and ibrutinib (GIVe). In RVe, GVe and GIVe, ven was added at cycle 1 day 22 (ramp up day 1) after a 21-day pretreatment with rituximab (1 dose), obinutuzumab (3 doses) or obinutuzumab (3 doses) plus ibrutinib (continuous) (Figure 1A). The safety population (i.e. all pts who received study treatment) of the ven-containing arms was used for this analysis. TLS was reported according to Cairo-Bishop criteria (Cairo M, Bishop M. Br J Haematol. 2004). For TLS risk evaluation, the most recent available CT/MRI and absolute lymphocyte count (ALC) were used. TLS risk was evaluated at baseline and at ramp up day 1, before the first dose of ven. The patients were categorized retrospectively according to the following TLS risk categories: high (any lymph node [LN] with largest diameter ≥10 cm or any LN with largest diameter ≥5 cm and ALC ≥25 G/L), intermediate (any LN ≥5 cm to