BTK and B-cell chronic lymphocytic leukemia: The European Society for Medical Oncology (ESMO) guidelines for front-line treatment of CLL include Bruton tyrosine kinase inhibitors (BTKi), namely ibrutinib and acalabrutinib, the B-cell lymphoma 2 inhibitor (BCL2i) venetoclax with or without obinutuzumab, and the phosphoinositide 3 kinase inhibitor (PI3Ki) idelalisib with rituximab, although the latter regimen is seldom used because of infectious toxicity [18].