The primary objective of this study is to compare progression-free survival (PFS), as assessed by blinded central review, of participants with advanced/metastatic human epidermal growth factor receptor 2 (HER2)-negative gBRCA mutation breast cancer when treated with niraparib as compared to those treated with physician's choice single agent chemotherapy standards (eribulin, vinorelbine, gemcitabine or capecitabine). PFS is defined as the date of randomization to the date of disease progression or death due to any cause, whichever occurs earlier as per Response evaluation criteria in solid tumors (RECIST) version (v)1.1 as determined by central review assessment. Progressive Disease is defined as at least a 20 percent (%) increase in the sum of diameters of measured lesions taking as references the smallest sum of diameters recorded on study (including Baseline) and an absolute increase of >= 5 millimeter (mm).

Centrally Confirmed intent-to-treat (ITT) Population is defined as all randomized participants with a central confirmation of germline BRCA mutation.

Overall Survival (OS) was defined as the time from randomization to the date of death of any causes.

Centrally Confirmed ITT Population

Blood samples were collected to evaluate central BRCA mutation status of participants. Baseline was defined as the most recent non-missing measurement prior to or on the first administration of study drug. Number of participants with central BRCA mutation status as BRCA1 positive only, BRCA2 positive only, Rearrangement only, BRCA1 and BRCA2 positive, BRCA1 positive and rearrangement, and BRCA2 positive and rearrangement were reported.

Centrally Confirmed ITT Population

An adverse event (AE) is any untoward medical occurrence that occurs in a participant or clinical investigation participant administered a pharmaceutical product, and which does not necessarily have to have a causal relationship with this treatment. An SAE is defined as any untoward medical occurrence or effect in a participant, whether or not considered related to the protocol treatment, at any dose that results in death, is life-threatening, requires inpatient hospitalization or prolongation of existing participant hospitalization, results in persistent or significant disability or incapacity, is a congenital anomaly or birth defect, is an medically important event or reaction as per medical and scientific judgment. Adverse events which were not serious adverse events were considered as non serious adverse events.

Safety Population comprised of all participants who started their allocated treatment (received at least one dose of allocated drug). Only those participants with data available at specified time point were analyzed.

PFS is defined as the date of randomization to the date of disease progression or death due to any cause, whichever occurs earlier as per RECIST version 1.1 as determined by Investigator assessment. Progressive Disease is defined as at least a 20 % increase in the sum of diameters of measured lesions taking as references the smallest sum of diameters recorded on study (including Baseline) and an absolute increase of >= 5 mm.

Centrally confirmed ITT Population

Time to treatment failure was defined from the date of randomization to progression or discontinuation of treatment for any reason, including but not restricted to disease progression, treatment toxicity and death.

Centrally Confirmed ITT Population

ORR was defined as the percentage of the participants who achieved a complete response (CR) or partial response (PR) to treatment evaluated using Response Evaluation Criteria in Solid Tumors (RECIST) v1.1. Complete Response (CR)=disappearance of all target and non-target lesions and normalization of tumor markers. Pathological lymph nodes must have short axis measures <10 mm. Partial Response (PR)= at least a 30% decrease in the sum of measures (longest diameter for tumor lesions and short axis measure for nodes) of target lesions, taking as reference the Baseline sum of diameters. Percentage values are rounded off up to 1 decimal.

Centrally Confirmed ITT population. Only those participants with confirmed response were analyzed.

Duration of response was defined as the time from first documentation of response (confirmed CR or PR) until the time of first documentation of disease progression by RECIST v1.1 or death by any cause.

Centrally Confirmed ITT population. Only those participants with confirmed response were analyzed.

The number of participants with MCID status in EORTC-QLQ-C30 was planned to be evaluated.The EORTC- QLQ-C30 includes 30-items with single and multi-item scales. These include five functional scales (physical functioning, role functioning cognitive functioning, emotional functioning and social functioning), three symptom scales (fatigue, pain and nausea/vomiting), a global health status (GHS)/ Quality-of-Life (QoL) scale, and six single items (constipation, diarrhea, insomnia, dyspnea, appetite loss and financial difficulties). Response options are 1 to 4. The average score can be transformed to 0 to 100, a high score for functional scales/ GHS/QoL represents better functioning ability or health-related quality-of-life (HRQoL), whereas a high score for symptom scales/ single items represents significant symptomatology.

ITT Population comprised of all randomized participants. This was an other pre-specified outcome measure. The results for this outcome measure will never be posted.

The number of participants with EQ-5D-5L scores by visit were planned to be evaluated. EQ-5D-5L is self-assessment questionnaire, consisting of 5 items covering 5 dimensions (mobility,self care, usual activities, pain/discomfort and anxiety/depression). Each dimension is measured by 5-point Likert scale(no problems, slight problems, moderate problems, severe problems and extreme problems). Responses for 5 dimensions together formed a 5-figure description of health state (e.g.11111 indicates no problems in all 5 dimensions). Each of these 5 figure health states were to be converted to a single index score. Range for EQ-5D-5L index score is 0 (worst health) to 100 (best health), higher the score better the health status.

ITT Population. This was an other pre-specified outcome measure. The results for this outcome measure will never be posted.

The number of participants with any subsequent therapies post-discontinuation of study treatment and association with potential survival related outcomes were planned to be evaluated.

Safety Population. This was an other pre-specified outcome measure. The results for this outcome measure will never be posted.

Biomarkers include germline and tumor mutations including somatic BRCA1 and 2 mutations, reversion mutations, loss of heterozygosity as well as genome landscape and transcriptional or functional measures of homologous recombination (HR) deficiency were planned to be evaluated.

Centrally Confirmed ITT Population. This was an other pre-specified outcome measure. The results for this outcome measure will never be posted.

Participants with germline BRCA1 and BRCA2 mutation status in association with survival related outcomes were planned to be evaluated.

Centrally Confirmed ITT Population. This was an other pre-specified outcome measure. The results for this outcome measure will never be posted.

The number of participants with serious adverse events related to new malignancy were reported.

Safety Population. Only those participants with data available at specified time were analyzed.

The number of participants with subsequent anticancer therapies were evaluated. Data has been reported as per following categories: any new anitumoral therapy, any chemotherapy, any radiotherapy, any surgery, any hormonal therapy, any targeted agents, and any other treatment. Participants may have received more than one subsequent therapies.

Safety Population. Only those participants with data available at specified time were analyzed.