Research has indicated that certain baseline molecular and cytogenetic characteristics, such as del(17p)/tumor protein p53 (TP53) mutations and complex karyotypes (23 chromosomal abnormalities), increase the risk of disease progression in patients with primary chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) undergoing treatment with ibrutinib. The gene discussed is TP53; the disease is B-cell chronic lymphocytic leukemia.