Nevertheless, the long-term safety for ibrutinib has not been established. Caution must be exercised for the development of resistant clones due to the persistence of the disease, because most patients treated with ibrutinib often have prolonged partial remissions. Moreover, about 2-5% of CLL patients will develop Richter's syndrome or transformation during the disease course and treatment. The rate of serious adverse events in patients who continued treatment for 1 year or longer was 43% in the first year of treatment and 32% after the first year. Within the first year of treatment, 8% patients discontinued therapy, while 6% discontinued therapy after the first year. Besides, considering that genetic mutations cause resistance to ibrutinib in CLL patients and altered signaling pathways are common mechanisms of resistance to single agents. It's expected to combine other agent with ibrutinib to obtain higher response in those CLL patients who have not obtained perfect effect and to relieve the toxicity from treatment of ibrutinib.