A Study of Etirinotecan Pegol (NKTR-102) Versus Treatment of Physician's Choice (TPC) in Patients With Metastatic Breast Cancer Who Have Stable Brain Metastases and Have Been Previously Treated With an Anthracycline, a Taxane, and Capecitabine

To compare Overall Survival (OS) of patients who receive 145 mg/m2 NKTR-102 given once every 21 days (q21d) with OS of patients who receive Treatment of Physician's Choice (TPC). Overall survival is defined as the time from the date of randomization to the date of death from any cause. Patients will be followed until their date of death or until final database closure. Patients who are lost-to-follow-up or are alive at the time of analysis will be censored at the time they were last known to be alive or at the date of event cut-off for OS analysis.

Progression-Free Survival (PFS) is defined as the time from the date of randomization to the earliest evidence of documented Progressive Disease (PD) or of death from any cause. The date of global deterioration or symptomatic deterioration will not be used as the date of PD. The assessment of PFS outside the CNS will utilize RECIST criteria v1.1.

Progression-Free Survival in Brain Metastasis (PFS-BM) is defined as the time from the date of randomization to the earliest evidence of documented Progressive Disease (PD) per Response Assessment in Neuro-Oncology-Brain Metastases (RANO-BM) in brain metastases or death from any cause. The PD will also be determined by the investigator's assessments. Progressive Disease (PD) is defined as at least a 20% increase in the sum of longest diameters of CNS target lesions, taking as reference the smallest sum on study. This included the baseline sum if that was the smallest on study. In addition to the relative increase of 20%, at least 1 lesion had to increase by an absolute value of 5 mm or more to be considered progression.

Progression-free survival (CNS and peripheral) is defined as the time from the date of randomization to the earliest evidence of documented PD in either the CNS or peripheral (using RANO-BM) or death from any cause. The PD will be determined by both the investigator's and the central imaging facility assessments. The same statistical methods that were used for PFS and PFS-BM will be used for PFS (Overall). Progressive Disease (PD) is defined as at least a 20% increase in the sum of longest diameters of CNS target lesions, taking as reference the smallest sum on study. This included the baseline sum if that was the smallest on study. In addition to the relative increase of 20%, at least 1 lesion had to increase by an absolute value of 5 mm or more to be considered progression.

RECIST criteria for lesions outside the Central Nervous System (CNS); RANO-BM criteria for CNS lesions) based upon the best response as assessed by the central imaging facility. CR is defined as disappearance of all target lesions. Any pathological lymph nodes (whether target or non-target) had to have reduction in short axis to < 10 mm. PR is defined as at least a 30% decrease in the sum of diameters of target lesions, taking as reference the baseline sum diameters. ORR is calculated as the sum of CR and PR. Progressive Disease (PD) is defined as at least a 20% increase in the sum of diameters of target lesions, taking as reference the smallest sum on study (this included the baseline sum if that was the smallest on study). Stable Disease (SD) is defined as neither sufficient shrinkage to qualify for PR nor sufficient increase to qualify for PD, taking as reference the smallest sum diameters while on study.

Clinical Benefit Rate will be defined as the proportion of patients having a Complete Response (CR), Partial Response (PR), or Stable Disease (SD) for at least 4 months (≥ 120 days). CR is defined as disappearance of all target lesions for at least 4 weeks with no new lesions, not use of corticosteroids, and patient was stable or improved clinically. PR is defined as at least a 30% decrease in the sum of longest diameters sustained for at least 4 weeks, no new lesions; stable to decreased corticosteroid dose; stable or improved clinically. Progressive Disease (PD) is defined as at least a 20% increase in the sum of diameters of target lesions, taking as reference the smallest sum on study (this included the baseline sum if that was the smallest on study). Stable Disease (SD) is defined as neither sufficient shrinkage to qualify for PR nor sufficient increase to qualify for PD, taking as reference the smallest sum diameters while on study.

Duration of response (DoR) outside the CNS will be defined as the time from first documented CR or PR until the earliest evidence of disease progression per RECIST v1.1 or death from any cause. CR is defined as disappearance of all target lesions for at least 4 weeks with no new lesions, not use of corticosteroids, and patient was stable or improved clinically. PR is defined as at least a 30% decrease in the sum of longest diameters sustained for at least 4 weeks, no new lesions; stable to decreased corticosteroid dose; stable or improved clinically. Progressive Disease (PD) is defined as at least a 20% increase in the sum of diameters of target lesions, taking as reference the smallest sum on study (this included the baseline sum if that was the smallest on study). Stable Disease (SD) is defined as neither sufficient shrinkage to qualify for PR nor sufficient increase to qualify for PD, taking as reference the smallest sum diameters while on study.

The EORTC QLQ-BN20 Scale has a series of 20 questions each of which involve reporting a scale from 1-4. It is an increasing scale where a score of one indicates "not at all" while a score of four indicates "very much". The minimum score is 20 and the maximum score is 80. The higher the score the worse the outcome.

The EQ-5D-5L scale is used to measure health by having a patient answer a series of questions. There are a series of 5 questions each of which is scaled from a score of 4-20 in increasing increments of 4. The scale is numbered from 0 to 100 where 100 means the beast health you can imagine and 0 means the worst health.

The Brief Fatigue Inventory scale utilizes a series of 4 questions. The first three are scored with a scale from 1-10. The fourth question has 6 six sub components each of which are scored with a scale of 1-10. For every scale, a score of 0 indicates no fatigue/interference where a score of 10 indicates as bad as you can imagine. A patient's score can range from 0 to 100 where 0 indicates the best outcome and 100 indicates the worst.

The magnitude of clinical benefit of NKTR-102 is assessed by the European Society for Medical Oncology Magnitude of Clinical Benefit Scale (ESMO-MCBS) (v1.0). The scale is graded 5, 4, 3, 2, 1, where grades 5 and 4 represent a high level of proven clinical benefit, and grade 1 represents no clinical benefit. To determine the magnitude of clinical benefit when the median OS with the standard of treatment is ≤ 1 year, the score is derived from the Hazard Ratio (HR) of Overall Survival, overall survival gain, and QoL improvement between two treatment arms. Values reported in the data table are Overall Survival values.

The number of participants with adverse events as assessed by Common Terminology Criteria for Adverse Events (CTCAE) v4.3