Time to best response is defined as the time from start of ibrutinib therapy until best objective response. Best response will be evaluated based on the following generally accepted algorithm: complete response greater than (>) partial response > partial response with lymphocytosis > stable disease > progressive disease.

Time to treatment discontinuation (TTD) will be calculated as the difference between ibrutinib initiation date and ibrutinib permanent discontinuation date.

The TTNT will be calculated as the difference between ibrutinib initiation date and initiation date of the first next therapy for CLL.

PFS is defined as the duration from date of ibrutinib initiation to date of disease progression (PD [according to the physician's evaluation]) or death from any cause. PD is defined as >= 50% increase in circulating lymphocyte count as per iwCLL criteria.

The OS in CLL participants will be measured and reported from start of ibrutinib therapy to the date of death (all-cause mortality); and from diagnosis to the date of death.

Number of participants with change in hematologic parameters (complete blood count, hemoglobin, leukocyte count, lymphocyte count, neutrophil count, platelet count) will be determined.

Number of participants with clinically significant change in biochemistry parameters (including lactate dehydrogenase [LDH] and creatinine clearance) will be determined.

Changes in the immunoglobulin levels from baseline will be reported.

Number of participants with at least one of the following conditions: lymphadenopathy, hepatosplenomegaly, bone marrow involvement, or B-symptoms as provided will be reported.

ECOG performance status is a standard criterion for measuring how the disease impacts daily living abilities. It describes the level of functioning in terms of the ability to care for oneself, daily activity, and physical ability (walking, working, etc). ECOG performance status score ranges from Grade 0 to 5: 0) Fully active and performances without restriction, 1) Restricted in physically strenuous activity, 2) Ambulatory and capable of all self-care but unable to carry out any work activities, 3) Capable of only limited self-care and confined to bed or chair more than 50% of waking hours, 4) Completely disabled, and 5) Dead.

An AE is any untoward medical event that occurs in a participant administered an investigational product, and it does not necessarily indicate only events with clear causal relationship with the relevant investigational product. An SAE is any AE that results in: death, persistent or significant disability/incapacity, requires inpatient hospitalization or prolongation of existing hospitalization, is life-threatening experience, is a congenital anomaly/birth defect and may jeopardize participant and/or may require medical or surgical intervention to prevent one of the outcomes listed above. Percentage of participants with AEs, all serious AEs, and all special situations (for example, medication error, overdosing, abuse, lack of effect, unexpected benefits following exposure to ibrutinib) will be reported.

The EQ-5D questionnaire is a brief, generic health-related quality of life assessment (HRQOL) that can also be used to incorporate participant preferences into health economic evaluations. The EQ-5D-5L descriptive system comprises the following 5 dimensions: mobility, self-care, usual activities, pain/discomfort and anxiety/depression and as overall health using a "thermometer" visual analog scale with response options ranging from 0 (worst imaginable health) to 100 (best imaginable health).

EORTC QLQ-30 designed to measure cancer patients' physical, psychological and social functions. It is composed of multi-item scales (physical, role, social, emotional and cognitive functioning) and single items (pain, fatigue, financial impact, appetite loss, nausea/vomiting, diarrhea, constipation, sleep disturbance and quality of life); high scores on the global and functional scales but low scores on the symptom scales indicate good QOL. QLQ-C30 has four-point scales for the first five items. These are coded with the same response categories as items 6 to 28, namely "Not at all", "A little", "Quite a bit" and "Very much." For items 29 and 30, a seven-point scale (ranging from 1 = "Very Poor" to 7 = "Excellent") rates overall health and overall quality of life.

Number of medical care encounters and treatments (including physician or emergency room visits, tests and procedures, and medications, surgeries and other procedures [such as computerized tomography {CT}, x-ray]) will be reported.

Duration of hospitalization is defined as number of days from the day of admission to discharge (total days length of stay), including duration by wards (for example, intensive care unit).

Duration of medical care encounters, including surgeries, and other selected procedures (inpatient and outpatient) will be reported.

Number of participants requiring blood and platelets transfusions will be reported.

Number of participants requiring erythropoietin and growth factor administrations will be reported.