Real-world outcomes of ponatinib treatment in 724 patients with CML and Ph+ ALL: a post-marketing surveillance study with a special interest in arterial occlusive events in Japan.

BACKGROUND: In September 2016, ponatinib was approved in Japan for the treatment of patients with chronic myeloid leukemia with resistance/intolerance to prior tyrosine kinase inhibitors and patients with relapsed or refractory Philadelphia chromosome-positive acute lymphoblastic leukemia. METHODS: We conducted a post-marketing all-case surveillance to study the safety and efficacy of ponatinib in clinical practice, focusing on arterial occlusive events. RESULTS: Data from 724 patients were collected for 2 years from the initiation of ponatinib. The arterial occlusive events were reported in 6.49% (47/724) with an exposure-adjusted incidence rate of 6.8/100 person-years. The risks associated with arterial occlusive events were age and comorbidities including hypertension and diabetes. At 104 weeks, the cumulative major molecular response rate in patients with chronic-phase chronic myeloid leukemia was 67.2% and the complete cytogenetic response in patients with Philadelphia chromosome-positive acute lymphoblastic leukemia was 80.0%. Furthermore, the estimated 1-year overall survival rate was 98.5% for chronic-phase chronic myeloid leukemia and 68.6% for Philadelphia chromosome-positive acute lymphoblastic leukemia. CONCLUSIONS: This surveillance demonstrated that ponatinib has a favorable safety and efficacy profile in Japanese patients and also showed the necessity of closely monitoring arterial occlusive events in older adults and patients with predisposing factors for atherosclerosis.

Post-marketing surveillance of the safety and effectiveness of nivolumab for classic Hodgkin lymphoma in Japan.

Nivolumab was approved for relapsed/refractory classic Hodgkin lymphoma (cHL) in Japan in 2016. After its approval, a prospective, non-interventional, observational post-marketing surveillance was initiated to evaluate the safety and effectiveness of nivolumab treatment for up to 12 months in patients with relapsed/refractory cHL. Of 304 registered patients, 288 were included in safety analyses and 282 in effectiveness analyses. There were 191 (66.3%) male patients, median age was 64.0 years, and 54 patients (18.8%) had performance status ≥ 2. Treatment-related adverse events (TRAEs) were reported in 183 (63.5%) patients, with grade 3-5 TRAEs in 86 (29.9%). The most common TRAEs were infusion reaction (14.6%), hepatic function abnormal (5.9%), interstitial lung disease (ILD) (5.6%), and hypothyroidism (5.2%). TRAEs of special interest in ≥ 5% of patients were infusion reaction (15.6%), hepatic failure/hepatic dysfunction/hepatitis/cholangitis sclerosing (13.2%), thyroid dysfunction (9.7%), and ILD (7.3%). In multivariable analyses, prior allogeneic hematopoietic stem cell transplantation was a risk factor for hepatic failure/hepatic dysfunction/hepatitis/cholangitis sclerosing, and prior thyroid gland disorders was a risk factor for thyroid dysfunction. The overall response rate was 61.7%. In conclusion, nivolumab showed a similar safety profile and comparable effectiveness to that reported in clinical trials for relapsed/refractory cHL (CheckMate 205, ONO-4538-15).

A phase 2 study of axicabtagene ciloleucel in relapsed or refractory large B-cell lymphoma in Japan: 1-year follow-up and biomarker analysis.

Axicabtagene ciloleucel (axi-cel) is an autologous, CD19-targeting chimeric antigen receptor T­cell therapy. We recently reported the 3-month follow-up results of a phase 2, multicenter, open­label, single-arm study of axi-cel in Japanese patients with relapsed or refractory (R/R) large B-cell lymphoma (LBCL) (JapicCTI-183914). Here, we present 1-year efficacy and safety data and biomarker analysis data regarding mechanisms of resistance to axi-cel. Primary and secondary endpoints included investigator-assessed objective response rate (ORR), serious adverse events, and treatment-emergent adverse events. Axi-cel pharmacokinetics were also examined. Biomarker analysis was performed by cytokine measurement, immunohistochemistry, RNA sequencing, and whole-exome sequencing. At a median follow-up of 13.4 months, ORR was 86.7% (13/15 patients), and the complete response (CR) rate improved to 53.3% (8/15 patients) due to response conversion. Seven patients experienced disease progression, and one achieved CR after re-treatment with axi-cel. No new safety concerns were detected. Plausible resistance mechanisms to axi-cel varied among patients but included CD19 downregulation, programmed death-ligand 1 upregulation, and increased macrophage and angiogenesis signatures. The 1-year efficacy and safety of axi-cel were confirmed in Japanese patients with R/R LBCL. Resistance to treatment may involve multiple factors, including target antigen loss and an unfavorable tumor environment.Clinical trial registration: Japan Clinical Trials Information; JapicCTI-183914.

Prospective screening for myocarditis in cancer patients treated with immune checkpoint inhibitors.

BACKGROUND: Immune checkpoint inhibitors (ICIs) improve clinical outcomes in various cancers, but sometimes induce autoimmune adverse effects, including myocarditis, which is the most serious complication. There are many reports on ICI-induced myocarditis; however, only a few prospective surveillance reports exist. Therefore, we developed a prospective screening protocol and performed monitoring clinically suspected myocarditis in every patient treated with ICIs. METHODS: We prospectively enrolled 126 consecutive patients treated with ICIs in this cohort. Outcomes of patients were determined and analyzed between April 2017 and May 2020. We evaluated vital signs, biomarkers, electrocardiograms, chest radiographs, and echocardiographs before and at 7 ±â€¯3, 14 ±â€¯3, 21 ±â€¯3, and 60 ±â€¯7 days after ICI initiation. RESULTS: Eighteen (14.3 %) presented troponin I elevation and 13 of them presented signs of clinically suspected myocarditis (10.3 %). Among the 13 patients, ICI was discontinued in four cases (3.2 %) without fatal events. Myocarditis appeared at an early stage of ICI treatment, regardless of severity (median, 44 days). CONCLUSIONS: We observed the frequency of patients with myocarditis or myocardial damage through a prospective screening program in the real world. Although the frequency was higher than expected, most cases were mild and ICI treatment could be continued under careful observation.

Safety and antitumor activity of copanlisib in Japanese patients with relapsed/refractory indolent non-Hodgkin lymphoma: a phase Ib/II study.

The safety, efficacy, and pharmacokinetics of copanlisib were evaluated in this phase Ib/II study in Japanese patients with relapsed/refractory indolent non-Hodgkin lymphoma (NHL). The primary endpoint was safety at the recommended dose; efficacy endpoints included objective response rate (ORR), progression-free survival (PFS), and overall survival. In phase Ib, patients received copanlisib 45 mg intravenously on days 1, 8, and 15 of a 28-day cycle, and when tolerated, consecutive patients received copanlisib 60 mg. As no dose-limiting toxicities occurred at the 45 mg (n = 3) or 60 mg (n = 7) dose in phase Ib, the recommended dose for Japanese patients was determined to be 60 mg, and this dose was used in phase II (n = 15). Although all patients experienced at least one treatment-emergent adverse event (TEAE), with hyperglycemia being the most common AE, no AE-related deaths were reported. The ORR was 68.0% (17/25 patients), median PFS was 302 (95% CI 231-484) days, and the duration of response was 330 (range 65-659) days. The pharmacokinetic properties of copanlisib were similar between Japanese and non-Japanese patients. Overall, copanlisib 60 mg had an acceptable safety profile and showed promising antitumor activity in Japanese patients with relapsed/refractory indolent NHL.

Phase 2 study of axicabtagene ciloleucel in Japanese patients with relapsed or refractory large B-cell lymphoma.

BACKGROUND: Axicabtagene ciloleucel (axi-cel) is an autologous chimeric antigen receptor T-cell based anti-CD19 therapy. The ZUMA-1 study, multicenter, single-arm, registrational Phase 1/2 study of axi-cel demonstrated high objective response rate in patients with relapsed/refractory large B-cell lymphoma. Here, we present the results of the bridging study to evaluate the efficacy and safety of axi-cel in Japanese patients (JapicCTI-183914). METHODS: This study was the phase 2, multicenter, open-label, single-arm trial. Following leukapheresis, axi-cel manufacturing and lymphodepleting chemotherapy, patients received a single infusion of axi-cel (2.0 × 106 cells/kg). Bridging therapy between leukapheresis and conditioning chemotherapy was not allowed. The primary endpoint was objective response rate. RESULTS: Among 17 enrolled patients, 16 received axi-cel infusion. In the 15 efficacy evaluable patients, objective response rate was 86.7% (95% confidence interval: 59.5-98.3%); complete response/partial response were observed in 4 (26.7%)/9 (60.0%) patients, respectively. No dose-limiting toxicities were observed. Grade ≥ 3 treatment-emergent adverse events occurred in 16 (100%) patients-most commonly neutropenia (81.3%), lymphopenia (81.3%) and thrombocytopenia (62.5%). Cytokine release syndrome occurred in 13 (81.3%) patients (12 cases of grade 1 or 2 and 1 case of grade 4). No neurologic events occurred. Two patients died due to disease progression, but no treatment-related death was observed by the data-cutoff date (October 23, 2019). CONCLUSION: The efficacy and safety of axi-cel was confirmed in Japanese patients with relapsed/refractory large B-cell lymphoma who have otherwise limited treatment options. TRIAL REGISTRATION: JapicCTI-183914.

Factors for the optimal selection of granulocyte colony-stimulating factor preparations and predictors for R-CHOP dose reductions/delays among patients with non-Hodgkin B-cell lymphoma (STOP FN in NHL 2 subanalysis).

BACKGROUND: A classification tree was used to analyze background factors for granulocyte colony-stimulating factor (G-CSF) preparation selection for febrile neutropenia (FN) prophylaxis in Japanese patients with non-Hodgkin B-cell lymphoma receiving the first R-CHOP cycle. METHODS: This was a subanalysis of the retrospective observational study STOP FN in NHL 2 (UMIN000029534). Patient characteristics, changes in neutrophil count, incidence and severity of neutropenia, and risk factors for dose reduction/delay of R-CHOP were assessed by G-CSF formulation. RESULTS: Among 234 patients in cycle 1, 25.6% received no G-CSF preparation, 52.1% received daily G-CSF, and 22.2% received pegfilgrastim. Pegfilgrastim use was most frequent among patients aged ≥ 80 years, while that of daily G-CSF was most frequent in patients with lymphocyte count (LC) < 1000 cells/µL. Changes in neutrophil count were more marked with pegfilgrastim compared with daily G-CSF and no G-CSF. Relevant factors for G-CSF preparation selection in the first R-CHOP cycle were age ≥ 80 years and LC < 1000 cells/µL; for chemotherapy dose reduction were FN onset in cycle 1 and female sex; and for dose delay was hemoglobin (< 12 g/dL). After cycle 2 and onward, pegfilgrastim use increased markedly (72.6%) compared with cycle 1 (22.2%), with significantly greater proportions continuing pegfilgrastim use and switching from daily G-CSF. CONCLUSION: Relevant factors for G-CSF preparation selection were age ≥ 80 years and LC < 1000 cells/µL. The use of pegfilgrastim increased markedly after cycle 2. These results may be useful for selecting appropriate G-CSF preparations in the first R-CHOP cycle. TRIAL REGISTRATION: UMIN000029534; registered on 13 October 2017, https://upload.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000033733 .

A phase I, dose-escalation study of oral PIM447 in Japanese patients with relapsed and/or refractory multiple myeloma.

PIM447, a pan-proviral integration site for Moloney leukemia (PIM) kinase inhibitor, has shown preclinical activity in multiple myeloma (MM). This phase I, open-label, multicenter, dose-escalation study aimed to determine the maximum tolerated dose (MTD) and recommended dose for expansion (RDE) of PIM447 in Japanese patients with relapsed and/or refractory (R/R) MM. The study included 13 patients (250 mg once daily (QD), [n = 7]; 300 mg QD, [n = 6]). The sole dose-limiting toxicity observed was grade 3 QTc prolongation in one patient from the 300 mg group, and the MTD and RDE was not determined. The most common suspected PIM447-related adverse events (AEs) included thrombocytopenia (76.9%), anemia (53.8%), and leukopenia (53.8%). All patients experienced at least one grade 3 or 4 AE, most frequently thrombocytopenia or leukopenia (61.5% each). The overall response rate was 15.4%, disease control rate 69.2%, clinical benefit rate 23.1%, and two patients had a partial response (one in each dose group). Two patients treated with 250 mg QD had a progression-free survival > 6 months. PIM447 250 mg or 300 mg QD was tolerated in Japanese patients with R/R MM. Further studies are required to evaluate clinical outcomes of PIM447 in combination with other drugs for the treatment of MM.Trial registration: clinicaltrials.gov: (NCT02160951).

Safety profile of brentuximab vedotin in Japanese patients with relapsed/refractory Hodgkin lymphoma or systemic anaplastic large cell lymphoma: a post-marketing surveillance study.

Brentuximab vedotin (BV) was initially approved in Japan for the treatment of relapsed/refractory (R/R) CD30-positive Hodgkin lymphoma (HL) and systemic anaplastic large cell lymphoma (sALCL). As requested by the Japanese Ministry of Health, Labour and Welfare, we conducted a post-marketing surveillance (PMS) study to assess the safety of BV in Japanese patients with R/R HL or sALCL. PMS forms were collected from 284 patients (182 with HL, 101 with sALCL and one with another lymphoma) treated between April and September 2014. The median age was 62 (range 14-93) years and the median number of treatment cycles was 5.5 for HL and 4 for sALCL. Adverse drug reactions (ADRs) were reported in 74.3% of patients. The most commonly observed ADRs included peripheral sensory neuropathy (39.1%; grade ≥ 3, 6.3%), neutropenia (34.5%; grade ≥ 3, 22.2%) and lymphopenia (7.0%; grade ≥ 3, 5.3%). Ten patients had fatal ADRs including interstitial lung disease (n = 3). This study showed that BV has an acceptable safety profile in Japanese patients with R/R HL and R/R sALCL in the clinical practice setting. However, close monitoring rare, but potentially fatal, ADRs such as pulmonary toxicity may be warranted, especially in patients with prior or ongoing pulmonary disorders.

The clonal evolution during long-term clinical course of multiple myeloma.

Somatic gene mutations related to acceleration disease and clonal evolution in multiple myeloma strongly influence severe clinical outcomes. In this study, we traced the transition of somatic mutations during the clinical course of myeloma patients over a long-term follow-up period (8.5 year average). Seven myeloma cases treated with immuno-chemotherapy at our institution were analyzed with clinical courses and the results of FISH and G-band analyses. Furthermore, the target sequences in regard to 121 genes, related to driver mutations or acceleration of disease in myeloma, were performed using bone marrow myeloma samples by next-generation sequencing, Ion Proton™ System. We detected a relationship between an increase in the dominant mutated gene (e.g., TP53, DIS3, FAM46C, KDM6B, and EGR1) and poor prognosis. In particular, clonal escalation of the TP53 mutation could not be overcome by any treatment. The selection of a combination treatment conducted in conjunction with the monitoring of gene mutations is appropriate for long-term survival. Our data demonstrate that long-term follow-up of somatic gene mutations during the clinical course of myeloma is helpful in the development of an effective treatment strategy.

New Concept of Onco-Hypertension and Future Perspectives.

Owing to aging populations, the prevalence of hypertension and associated cardiovascular events has been increasing worldwide. The morbidity and mortality due to cancer have also been increasing with aging populations. Several small-molecule inhibitors have been used in cancer therapy, which have a positive impact on the prognosis and survival of patients with cancer. Consequently, the number of cancer survivors with hypertension has been rapidly increasing. Anticancer therapy, including vascular endothelial growth factor inhibitors, increases blood pressure. However, both clinical and laboratory evidence are lacking regarding optimal blood pressure control in patients with hypertension with cancer. Here, we propose the concept of onco-hypertension, which is an evolving subspecialty focused on the complex pathophysiology of hypertension and cancer. In this review, we highlight blood pressure changes in cancer, hypertension induced by anticancer therapy, and optimal blood pressure management in patients with hypertension with cancer. In addition, we discuss needed studies to further establish this new onco-hypertension concept.

Phase I, multicenter, dose-escalation study of avadomide in adult Japanese patients with advanced malignancies.

Non-Hodgkin lymphoma (NHL) treated with chemoimmunotherapy has limited efficacy in some patients, resulting in relapsed or refractory disease. Avadomide (CC-122) is a novel cereblon-binding agent that exhibits antilymphoma and immune-modulation activities with a biological profile distinct from similar agents, such as lenalidomide. This phase I multicenter study evaluated avadomide in Japanese patients with advanced solid tumors or NHL. Fourteen patients with NHL and one with a solid tumor (esophageal carcinoma), were enrolled in four dose-escalation cohorts using a 3 + 3 design. Primary endpoints included safety, dose-limiting toxicities (DLT), maximum-tolerated dose and/or recommended phase II dose (RP2D), and pharmacokinetics. Secondary endpoints included overall response rate (ORR) and duration of response. One patient with NHL experienced DLT, which included face edema, pharyngeal edema, and tumor flare (all grade 1) that led to a dose reduction. Eleven patients had grade ≥3 treatment-emergent adverse events, most frequently decreased neutrophil count (33%) and decreased lymphocyte count (20%). The ORR in patients with NHL (n = 13) was 54%, including four complete and three partial responses. The best response for the solid tumor patient was progressive disease. Avadomide dose intensity was consistent across cohorts, and the 3-mg dose given five consecutive days/week was established as the RP2D. This phase I study identified a tolerable dose of avadomide, with an acceptable toxicity profile and clinically meaningful efficacy in Japanese patients with previously treated NHL.

Safety and pharmacokinetics of polatuzumab vedotin in Japanese patients with relapsed/refractory B-cell non-Hodgkin lymphoma: a phase 1 dose-escalation study.

OBJECTIVE: A phase 1 dose-escalation study of polatuzumab vedotin (pola) was conducted to assess safety, pharmacokinetics and preliminary antitumor activity of pola in Japanese patients with relapsed/refractory B-cell non-Hodgkin lymphoma. METHODS: Patients received pola (1.0 or 1.8 mg/kg) intravenously every 21 days until disease progression or intolerance. Intra-patient dose escalation was prohibited. Tolerability was determined by the standard 3 + 3 rule. Blood sampling was performed to characterize pharmacokinetics. Antitumor activity was evaluated through computed tomography and bone marrow sampling. RESULTS: Four patients received pola 1.0 mg/kg; three received 1.8 mg/kg. Patients had follicular lymphoma (n = 4) or diffuse large B-cell lymphoma (n = 3), median age of 62 years, received a median of 3 prior therapies; six were female. Pola was well tolerated in both cohorts, with no dose-limiting toxicities observed. The most common adverse event was peripheral sensory neuropathy (n = 4). Grade 3 adverse events were cholecystitis and neutrophil count decreased (one each; both 1.0 mg/kg), and syncope and cataract (one each; both 1.8 mg/kg). The plasma half-life of antibody-conjugate monomethyl auristatin E was 4.43-7.98 days, and systemic exposure of unconjugated monomethyl auristatin E was limited in both cohorts. Four patients achieved objective responses (three complete, one partial) without disease progression during the study. CONCLUSIONS: This phase 1 dose-escalation study demonstrated that pola has an acceptable safety profile and offers encouraging antitumor activity to Japanese patients with relapsed/refractory B-cell non-Hodgkin lymphoma. Pola 1.8 mg/kg, the recommended phase 2 dose, was tolerable in Japanese patients.

Cost-effectiveness analysis of treatment regimens with obinutuzumab plus chemotherapy in Japan for untreated follicular lymphoma patients.

AIMS: Obinutuzumab (GA101; G) is a new treatment for follicular lymphoma (FL) that is anticipated to have greater efficacy than the current treatment, rituximab (R). The aim of this study was to evaluate the cost-effectiveness of G plus chemotherapy (G + Chemo) against that of R plus chemotherapy (R + Chemo) for patients in Japan with previously untreated FL. MATERIALS AND METHODS: We localized a previously reported cost-effectiveness model using the Japanese cost data. For estimating costs adapted in the model, FL patients treated with R were identified from Japanese hospital-based claims database and classified into three treatment regimen groups according to chemotherapies used with R: CHOP, CVP, and bendamustine (B). Based on services per patient and cost items, parameters determining the cost amounts were derived using a multivariate generalized linear mixed model to estimate the direct medical costs for each treatment regimen group for G and R. For the utility, same values in the previous model were used. Lifetime cost and quality-adjusted life year (QALY) were estimated under the payer's perspective. RESULTS: The calculated incremental cost-effectiveness ratios (ICERs) in million JPY per QALY for G-CHOP vs. R-CHOP, G-CVP vs. R-CVP, and G-B vs. R-B were 5.4, 4.3, and 4.8, respectively. ICERs were lower than 7.5 million JPY per QALY, which is the cost-effectiveness threshold for cancer treatments, and showed that G + Chemo is a cost-effective treatment regimen for Japanese patients with previously untreated FL. Lifetime direct medical costs were lowest in the R-B group because hospitalization costs that accounted for most of the total cost were lowest in this group. Limitations and conclusions: The cost-effectiveness of G + Chemo is acceptable in Japan. Differences in the direct medical costs among treatment regimen groups were mostly due to hospitalization costs. This is probably because many Japanese hematologists choose inpatient treatments over outpatient treatments in CHOP-based induction therapy.

Incidence and risk factors for febrile neutropenia in Japanese patients with non-Hodgkin B cell lymphoma receiving R-CHOP: 2-year experience in a single center (STOP FN in NHL 2).

BACKGROUND: Myelosuppressive chemotherapy-induced febrile neutropenia (FN) is a life-threatening condition. Patients receiving granulocyte colony-stimulating factors (G-CSF) have shorter duration of neutropenia, faster recovery from fever, and shorter duration of antibiotics use. Most strategies for FN prevention using daily G-CSF and pegfilgrastim are based on overseas studies. Data on Japanese patients were lacking; thus, we previously determined the incidence of FN in non-Hodgkin B cell lymphoma (B-NHL) patients at our center. Here, we aimed to gain additional insights into pegfilgrastim use in this population. METHODS: This single-center, retrospective, observational study (STOP FN in NHL 2) enrolled patients with B-NHL who underwent a regimen comprising rituximab and CHOP therapy over a 2-year period (January 2015-June 2017). The incidence of FN in cycle 1 of chemotherapy, risk factors for FN development, and use of daily G-CSF and pegfilgrastim were evaluated. RESULTS: We evaluated 239 patients: 61 patients did not receive G-CSF and 178 received G-CSF. The incidence of FN was 10.5% (95% confidence interval [CI] 6.9-15.1%) in cycle 1 and 13.0% (95% CI 9.0-17.9%) in all cycles. The FN incidence was significantly lower (P = 0.0008) in patients receiving daily G-CSF and pegfilgrastim than patients not receiving G-CSF. Significant risk factors for FN were age ≥ 65 years, albumin < 3.5 g/dL, hemoglobin < 12 g/dL, and no prophylaxis with daily G-CSF/pegfilgrastim during cycle 1. CONCLUSIONS: The incidence of FN in cycle 1 and in all cycles and the identified risk factors were similar with those we previously reported; thus, our results validate previous findings. TRIAL REGISTRATION: UMIN000029534.

Elotuzumab plus lenalidomide and dexamethasone for newly diagnosed multiple myeloma: a randomized, open-label, phase 2 study in Japan.

Novel therapies are needed for patients with newly diagnosed multiple myeloma (NDMM). Elotuzumab plus lenalidomide and dexamethasone (ELd) is approved for the treatment of relapsed/refractory multiple myeloma (RRMM). This phase 2 study in Japan evaluated ELd vs lenalidomide and dexamethasone (Ld) in patients with NDMM who were ineligible for stem cell transplantation. Elotuzumab infusion was accelerated to 5 mL/min by dose 3, cycle 1, allowing most subsequent infusions to be completed within 1 h. The primary endpoint was overall response rate (ORR) in the ELd arm. Secondary endpoints were the difference in ORR between treatments, and progression-free survival (PFS). Patients were randomized to ELd (n = 40) or Ld (n = 42); median number of treatment cycles was 13 (ELd) and 12 (Ld). In the ELd arm, ORR was 88% [70% confidence interval (CI) 80-93]. The estimated difference in ORR between treatments was 13% (95% CI - 4, 30) in favor of ELd. Progression-free survival data were immature. Safety was consistent with previous findings of ELd in Japanese patients with RRMM. No infusion reactions occurred at the maximum rate of 5 mL/min, which was used in 89% of elotuzumab infusions. ELd may be an effective, well-tolerated frontline treatment for patients with NDMM ineligible for stem cell transplantation.

Phase I study of ibrutinib in Japanese patients with treatment-naïve chronic lymphocytic leukemia/small lymphocytic lymphoma.

This phase I study evaluated the safety and efficacy of single-agent ibrutinib in Japanese patients with treatment-naïve chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (aged 20-69 years and ineligible for chemotherapy using fludarabine or cyclophosphamide, or aged ≥70 years). Eight patients received oral ibrutinib 420 mg once daily until progressive disease or unacceptable toxicity. The primary endpoint was safety; secondary endpoints included the overall response rate (ORR). At the time of final analysis (August 22, 2018), eight patients (all with CLL; median age, 68.5 years) had received ibrutinib for a median of 32.2 months (range, 10.4-35.9); all patients had discontinued study treatment, with 50.0% of patients switching to marketing-approved ibrutinib as subsequent anticancer therapy. All patients had ≥1 adverse event (AE); the most common AEs included a decreased platelet count, upper respiratory tract infection, increased lymphocyte count, diarrhea, nasopharyngitis, peripheral edema and rash. Four patients (50.0%) had a total of eight grade ≥3 AEs, most commonly lung infection and decreased neutrophil count. Eight serious AEs were reported in four patients (50.0%); these included a case of muscle hemorrhage (grade 3), decreased neutrophil count (grade 4) that led to dose reduction and one case of fatal cardiac arrest. The ORR was 87.5% (7/8 patients [exact 95% confidence interval 47.3-99.7]). One patient had a complete response, six had a partial response and one had a partial response with lymphocytosis. Ibrutinib had an acceptable safety profile and high ORR in Japanese patients with treatment-naïve CLL.