Venetoclax-based regimens have expanded the therapeutic options for patients with chronic lymphocytic leukemia (CLL), frequently achieving remissions with undetectable measurable residual disease (uMRD) and facilitating time-limited treatment without utilizing chemotherapy. Although response rates are high and durable disease control is common, longer-term follow-up of patients with relapsed and refractory (RR) disease, especially in the presence of TP53 aberrations, demonstrates frequent disease resistance and progression. Although the understanding of venetoclax resistance remains incomplete, progressive disease (PD) is typified by oligoclonal leukemic populations with distinct resistance mechanisms, including BCL2 mutations, upregulation of alternative BCL2 family proteins and genomic instability. Although most commonly observed in heavily pre-treated patients with disease refractory to fludarabine and harboring complex karyotype (CK), Richter transformation (RT) presents a distinct and challenging manifestation of venetoclax resistance. For patients with progressive CLL after venetoclax, treatment options include B-cell receptor pathway inhibitors (BCRis), allogeneic stem cell transplantation (SCT), chimeric antigen receptor (CAR) T-cells, and venetoclax re-treatment for those with disease relapsing after time-limited therapy. However, data to inform clinical decisions for these patients are limited. We review the biology of venetoclax resistance and outline an approach to the common clinical scenarios encountered after venetoclax-based therapy that will increasingly confront practising clinicians.
Thomas E Lew, Constantine S Tam, John F Seymour