The Role of BTK Inhibition in the Treatment of Chronic Lymphocytic Leukemia: A Clinical View.

The B cell receptor (BCR) signaling pathway is functional and has critical cell survival implications in B cell malignancies, such as chronic lymphocytic leukemia (CLL). Orally administered small molecule tyrosine kinase inhibitors of members of the BCR signaling pathway have proven to be transformational in treatment of CLL. The first-generation inhibitor, ibrutinib, covalently binds to the C481 amino acid of Bruton's tyrosine kinase (BTK), thereby irreversibly inhibiting its kinase activity, and interferes with the biology of the cells, ultimately resulting in CLL cell death and therapeutic response. Remissions are not deep to the point of considering discontinuation for most patients, but BTK-inhibitor-based therapy provides exceptional long-term disease control with continuous treatment. There are in-class toxicities and more selective second- and subsequent-generation agents and reversible inhibitors have been developed with the intent of reducing toxicities. Also, strategies to subvert resistance have included tighter or alternative, non-covalent, inhibitor binding. Furthermore, other strategies to deplete BTK protein, such as degraders, are in development and being tested in the clinic. Ultimately, the development and approval of these agents targeting BTK have ushered in a new era of chemotherapy-free treatments with remarkably improved survival outcomes for patients with CLL.

Treating Leukemia in the Time of COVID-19.

The coronavirus disease 2019 (COVID-19) pandemic poses several challenges to the management of patients with leukemia. The biology of each leukemia and its corresponding treatment with conventional intensive chemotherapy, with or without targeted therapies (venetoclax, FLT3 inhibitors, IDH1/2 inhibitors, Bruton's tyrosine kinase inhibitors), introduce additional layers of complexity during COVID-19 high-risk periods. The knowledge about COVID-19 is accumulating rapidly. An important distinction is the prevalence of "exposure" versus "clinical infectivity," which determine the risk versus benefit of modifying potentially highly curative therapies in leukemia. At present, the rate of clinical infection is <1-2% worldwide. With a mortality rate of 1-5% in CO-VID-19 patients in the general population and potentially of >30% in patients with cancer, careful consideration should be given to the risk of COVID-19 in leukemia. Instead of reducing patient access to specialized cancer centers and modifying therapies to ones with unproven curative benefit, there is more rationale for less intensive, yet effective therapies that may require fewer clinic visits or hospitalizations. Here, we offer recommendations on the optimization of leukemia management during high-risk COVID-19 periods.