- Histologically and/or cytologically confirmed diagnosis of Estrogen Receptor-Positive
(ER+) and/or Progesterone Receptor-Positive (PR+) breast cancer by local laboratory.
- Human Epidermal growth factor Receptor 2 Negative (HER2-) breast cancer defined as a
negative in situ hybridization test or an Immunohistochemistry (IHC) status of 0, 1+
or 2+. If IHC is 2+, a negative In Situ Hybridization (Fluorescence [FISH],
Chromogenic [CISH], or Silver [SISH]) test is required by local laboratory testing.
- Participants are allowed (but not required) to have up to two lines of prior
chemotherapy regimens in the metastatic setting for the dose expansion phase. For the
dose escalation cohort, up to three previous lines of chemotherapy in the metastatic
setting is acceptable.
- Measurable disease, i.e., at least one measurable lesion as per Response Evaluation
Criteria in Solid Tumors (RECIST)1.1 criteria only *for expansion cohorts.
- For *escalation cohorts, bone only disease is allowed. For expansion cohorts, there
must be measurable disease as stated above.
- Eastern Cooperative Oncology Group Performance Status (ECOG PS) 0 or 1.
- Written informed consent must be obtained prior to any screening procedures and
according to local guidelines.
- Adequate bone marrow and organ function.
- Must be able to swallow ribociclib and Tamoxifen capsules/tablets.
- Pre-Menopausal Women Eligibility: 1) Pre-menopausal women who received adjuvant
Aromatase Inhibitor and Ovarian Suppression (AI + OS) in the adjuvant setting and
completed at least 12 months of hormonal therapy. 2) Pre-menopausal women with de novo
metastatic disease are eligible if they have had no prior endocrine therapy. 3)
Pre-menopausal women who have not received Tamoxifen in the metastatic setting, but
have received up to two lines of chemotherapy.
- Post-Menopausal Women and Men Eligibility: 1) Post-menopausal women or men who have
progressed on first-line or second line therapy with an aromatase inhibitor in the
metastatic setting. 2) Post-menopausal women or men who have recurred while on or
after completion of adjuvant treatment with aromatase inhibitors (they have completed
at least one year of AI in the adjuvant setting before progression on AI). 3)
Post-menopausal women or men who are not considered candidates for treatment with an
aromatase inhibitory by their oncologist, patients not willing to go on AI, or
patients who were intolerant to AI.
- Post-menopausal women or men are allowed (but not required) to have up to two lines of
prior chemotherapy regimens in the metastatic setting for the dose expansion phase .
For the dose escalation cohort, up to three previous lines of chemotherapy in the
metastatic setting is acceptable.
- Potential participants with inflammatory breast cancer.
- Prior CDK 4/6 inhibitor exposure.
- Have received Tamoxifen in the metastatic setting (for more than 30 days) or has
progressed while on Tamoxifen in the adjuvant setting.
- Known hypersensitivity to ribociclib or excipients of tamoxifen.
- A concurrent malignancy or malignancy within 3 years of starting study drug, with the
exception of adequately treated, basal or squamous cell carcinoma, non-melanomatous
skin cancer or curatively resected cervical cancer.
- Central nervous system (CNS) involvement unless specific criteria are met.
- Impairment of Gastrointestinal (GI) function or GI disease that may significantly
alter the absorption of the study drugs (e.g., ulcerative diseases, uncontrolled
nausea, vomiting, diarrhea, malabsorption syndrome, or small bowel resection).
- Known history of HIV infection (testing not mandatory).
- Any other concurrent severe and/or uncontrolled medical condition that would, in the
investigator's judgment, cause unacceptable safety risks, contraindicate patient
participation in the clinical study or compromise compliance with the protocol (e.g.
chronic pancreatitis, chronic active hepatitis, active untreated or uncontrolled
fungal, bacterial or viral infections, etc.).
- Clinically significant, uncontrolled heart disease and/or a recent events as specified
in the study protocol
- Currently receiving any of the following medications and cannot be discontinued 7 days
prior to starting study drug: a. Known strong inducers or inhibitors of CYP3A4/5,
including grapefruit, grapefruit hybrids, pummelos, star-fruit, and Seville oranges.
b. That have a narrow therapeutic window and are predominantly metabolized through
CYP3A4/5. c. That have a known risk to prolong the QT interval or induce Torsades de
Pointes. d. Herbal preparations/medications, dietary supplements not prescribed by an
- Currently receiving or has received systemic corticosteroids ≤2 weeks prior to
starting study drug, or who have not fully recovered from side effects of such
- The following uses of corticosteroids are permitted: single doses, topical
applications (e.g., for rash), inhaled sprays (e.g., for obstructive airways
diseases), eye drops or local injections (e.g., intra-articular).
- Currently receiving warfarin or other coumarin-derived anticoagulant for treatment,
prophylaxis or otherwise. Therapy with heparin, low molecular weight heparin (LMWH) or
fondaparinux is allowed.
- Participation in a prior investigational study within 30 days prior to enrollment..
- Has received radiotherapy ≤ 4 weeks or limited field radiation for palliation ≤ 2
weeks prior to starting study drug, and who has not recovered to grade 1 or better
from related side effects of such therapy (exceptions include alopecia) and/or in whom
≥ 25% of the bone marrow was irradiated.
- Has had major surgery within 14 days prior to starting study drug or has not recovered
from major side effects (tumor biopsy is not considered as major surgery).
- Has not recovered from all toxicities related to prior anticancer therapies to NCI
Common Terminology Criteria for Adverse Events (CTCAE) version 4.03 Grade equal to or
less than 1 (Exception to this criterion: patients with any grade of alopecia are
allowed to enter the study).
- A Child-Pugh score B or C.
- History of non-compliance to medical regimen or inability to grant consent.
- Pregnant or nursing (lactating) women, where pregnancy is defined as the state of a
female after conception and until the termination of gestation, confirmed by a
positive human Chorionic Gonadotropin (hCG) laboratory test.]
- Women of child-bearing potential, defined as all women physiologically capable of
becoming pregnant, unless they are using highly effective methods of contraception
throughout the study and for 12 weeks after study drug discontinuation. There are
specific guidelines regarding the various acceptable highly effective contraception
methods. Note: The use of oral contraception is not allowed.