The purpose of this study is to determine whether denosumab compared to placebo, will reduce the rate of first clinical fracture in women with non-metastatic breast cancer receiving (non-steroidal) aromatase inhibitor therapy.

Participants will remain on treatment until the required number of events (where an event is defined as first clinical fracture) is reached and all participants have had the opportunity to receive a minimum of at least 2 doses of study drug, whichever occurs later. The primary analysis data cut-off date (PADCD) is defined as the time at which the required number of events is reached and all participants have had the opportunity to receive at least 2 doses of study drug. When the PADCD is reached, all participants will discontinue study drug.

Following the study PADCD, participants will be followed every 12 months starting from their last study visit until a maximum of 66 months after PADCD.

After approval of Amendment 4, willing and eligible participants randomized to placebo during the double-blind phase may participate in an open-label phase (OLP) and receive denosumab 60 mg Q6M for up to 36 months (maximum of 7 doses).

After approval of Amendment 6 in 2019 a zoledronic acid (ZA) substudy was added to the protocol. Willing and eligible participants who participated in the OLP of the study and completed open-label denosumab may opt in to this ZA substudy and either receive a single dose of ZA (Therapy Arm), or be managed according to the current standard of care for this patient population (Control Arm).

Inclusion Criteria for Double Blinded Phase:

• Histologically or cytologically confirmed adenocarcinoma of the breast;

• Female subjects with non-metastatic disease who are estrogen receptor (ER) and/or progesterone receptor (PR) positive, and who have completed their treatment pathway;

• Subjects who are currently on, or will initiate an approved non-steroidal aromatase inhibitor therapy (eg, anastrazole) in the adjuvant setting;

• Postmenopausal woman, defined as a woman fulfilling any one of the following criteria:

  • Having undergone a bilateral oophorectomy;
  • Age ≥ 60 years;
  • Aged < 60 years meeting the following requirements:

• Follicle-stimulating hormone (FSH) and estradiol in the postmenopausal range;

• A negative pregnancy test within 7 days prior to randomization. Subjects who have undergone a hysterectomy do not require a pregnancy test.

• More criteria may apply.

Exclusion Criteria for Double Blinded Phase:

• Aromatase inhibitor therapy for more than 24 months;
• Prior or concurrent treatment with Selective Estrogen Receptor Modulators (eg, tamoxifen);
• Evidence of metastatic disease;
• Current or prior intravenous (IV) bisphosphonate administration;
• Oral bisphosphonate treatment greater than or equal to 3 years continuously OR greater than 3 months but less than 3 years unless there was a washout period of at least 1 year prior to randomization OR any use during the 3-month period prior to randomization;
• Prior administration of denosumab;
• Known liver or renal deficiency;
• Recurrence of the primary malignancy (e.g., during the allowed interval of pretreatment with aromatase inhibitor);
• Diagnosis of any second non-breast malignancy within the last 5 years, except for adequately treated basal cell or squamous cell skin cancer, or for in situ carcinoma of the cervix uteri;
• Any kind of disorder that compromises the ability to give written informed consent and/or comply with study procedures.

Inclusion Criteria to Receive Open-label Phase Denosumab:

• Obtain signed and dated written informed consent prior to performing any study-specific procedure;
• Subjects currently taking an approved non-steroidal AIT (eg, anastrazole) or who have completed or discontinued AIT within 12 months prior to participation in the OLP;
• Randomized to placebo arm during the double-blind phase (as determined by unblinding procedures);

Exclusion Criteria to Receive Open-label Phase Denosumab:

• Current or prior IV bisphosphonate administration;

• Subjects meeting the following criteria for oral bisphosphonate treatment:

  • Greater than or equal to 3 years continuously,
  • Greater than 3 months but less than 3 years unless subject has had a washout period of at least 1 year prior to participation in the OLP,
  • Any use during the 3-month period prior to participation in the OLP;

• Prior or concurrent treatment with SERMs (eg, tamoxifen);

• Subjects who ended treatment with investigational product (IP) prematurely in the double-blind phase; Treatment with commercial denosumab (Prolia or Xgeva) prior to participation in the OLP.

Eligibility for ZA substudy Inclusion Criteria

• Obtain signed and dated written informed consent prior to performing any substudy-specific procedure

• Subjects that received OLP denosumab and completed OLP treatment

• Last OLP denosumab administration no longer than 9 months ago Exclusion Criteria

• Current or prior ZA administration.

• Subjects who ended treatment with investigational product (IP) prematurely in the double-blind phase and OL phase

• Known sensitivity or intolerance to any of the products to be administered during the substudy (eg, ZA, calcium or vitamin D)

• Known history of any of the following conditions either by subject self report or chart review

  • Paget's disease (bone), Cushing's disease, hyperprolactinemia or other active metabolic bone disease
  • Known history of hypocalcemia
  • Major surgery, or significant traumatic injury occurring within 4 weeks prior to randomization
  • Parathyroid glands in neck surgically removed.
  • Any sections of intestine removed.
  • Known human immunodeficiency virus infection
  • Active infection with hepatitis B or hepatitis C virus

• Known liver or renal disease as determined by the investigator and indicated by the following criteria:

  • Aspartate aminotransferase ≥ 2.5 x ULN
  • Alanine transaminase ≥ 2.5 x ULN
  • Serum creatinine ≥ 2 x ULN
  • Creatine clearance < 35ml/min Subjects that are pregnant or breastfeeding
  • All subjects with reproductive potential must have a negative pregnancy test within 7 days before randomization

• Subjects who are osteoporotic in baseline BMD

De-identified individual patient data for variables necessary to address the specific research question in an approved data sharing request

Data sharing requests relating to this study will be considered beginning 18 months after the study has ended and either 1) the product and indication (or other new use) have been granted marketing authorization in both the US and Europe or 2) clinical development for the product and/or indication discontinues and the data will not be submitted to regulatory authorities. There is no end date for eligibility to submit a data sharing request for this study.

Qualified researchers may submit a request containing the research objectives, the Amgen product(s) and Amgen study/studies in scope, endpoints/outcomes of interest, statistical analysis plan, data requirements, publication plan, and qualifications of the researcher(s). In general, Amgen does not grant external requests for individual patient data for the purpose of re-evaluating safety and efficacy issues already addressed in the product labelling. Requests are reviewed by a committee of internal advisors, and if not approved, may be further arbitrated by a Data Sharing Independent Review Panel. Upon approval, information necessary to address the research question will be provided under the terms of a data sharing agreement. This may include anonymized individual patient data and/or available supporting documents, containing fragments of analysis code where provided in analysis specifications. Further details are available at the link below.