Pembrolizumab Letrozole and Palbociclib in Treating Postmenopausal Patients With Newly Diagnosed Metastatic Stage IV Estrogen Receptor Positive Breast Cancer

  • End date
    Dec 31, 2021
  • participants needed
  • sponsor
    City of Hope Medical Center
Updated on 19 February 2021
monoclonal antibodies
measurable disease
breast cancer
treatment regimen
international normalized ratio
neutrophil count
liver metastasis
tumor cells
monoclonal antibody therapy
biomarker analysis
estrogen receptor
her2-negative breast cancer


This phase II trial studies how well pembrolizumab works when given together with letrozole and palbociclib in treating postmenopausal patients with newly diagnosed stage IV estrogen receptor positive breast cancer that has spread to other parts of the body (metastatic). Immunotherapy with monoclonal antibodies, such as pembrolizumab, may help the body's immune system attack the cancer, and may interfere with the ability of tumor cells to grow and spread. Estrogen can cause the growth of breast cancer cells. Antihormone therapy, such as letrozole, may lessen the amount of estrogen made by the body. Palbociclib may stop the growth of tumor cells by blocking some of the enzymes needed for cell growth. Giving pembrolizumab, letrozole, and palbociclib may be an effective treatment for patients with stage IV estrogen receptor positive breast cancer.



I. To evaluate the objective response rate (ORR), based on Response Evaluation Criteria in Solid Tumors [RECIST], version 1.1), of pembrolizumab in combination with letrozole and palbociclib in patients with newly diagnosed metastatic estrogen receptor (ER)+human epidermal growth factor receptor (HER)2- breast cancer, and determine if the addition of pembrolizumab to letrozole and palbociclib combination can achieve an improved response rate (ORR = complete response [CR] + partial response [PR]) measured from the study baseline, based on RECIST version 1.1.


I. To determine the safety and tolerability of adding pembrolizumab (200 mg every 3 weeks) to letrozole (2.5 mg) and palbociclib (125 mg 3 weeks on, one week off) in patients with metastatic ER+HER2- breast cancer.

II. To evaluate the CR rate.

III. To evaluate progression-free survival (PFS).

IV. To evaluate overall survival (OS).

V. To evaluate duration of response (DOR) using RECIST version 1.1.

VI. To evaluate clinical benefit rate (CBR) using RECIST version 1.1.

VII. To evaluate toxicities (using the National Cancer Institute [NCI] Common Terminology Criteria for adverse Events [CTCAE], version 4.0) associated with the triple drug combination (pembrolizumab, letrozole, and palbociclib) in patients with metastatic ER+HER2- breast cancer.

VIII. To evaluate CR, PR, ORR, PFS, DOR, and CBR using immune-related Response Criteria In Solid Tumors (irRECIST); time to treatment failure will also be assessed.


I. To study cellular/humoral immune response by analyzing immune and stromal cell characteristics before and after treatment that correlate with clinical response; this includes programmed cell death 1 ligand 1 (PD-L1) expression levels.

II. To study the peripheral serum thymidine kinase (TK) level and its association with treatment response.

III. To study circulating tumor deoxyribonucleic acid (DNA) (ctDNA) and the effect of combining pembrolizumab, letrozole, and palbociclib on ctDNA profiles.

IV. To evaluate genomic and phenotypic status of breast tumor.


Patients receive letrozole orally (PO) once daily (QD) on days 1-28 and palbociclib PO QD for 3 weeks. Cycless with letrozole and palbociclib repeat every 28 days in the absence of disease progression or unacceptable toxicity. Patients also receive pembrolizumab intravenously (IV) over 30 minutes on day 1. Cycles with pembrolizumab repeat every 21 days in the absence of disease progression or unacceptable toxicity.

After completion of study treatment, patients are followed up at 30 days, every 6 months for 3 years, and then every 12 months for 1 year.

Condition Metastatic Breast Cancer, Estrogen Receptor Positive, Postmenopausal, Stage IV Breast Cancer, Recurrent Breast Carcinoma, HER2/Neu Negative, Metastatic Breast Carcinoma, HER2/Neu Negative, HER2/Neu Negative, HER2/Neu Negative, HER2/Neu Negative, HER2/Neu Negative, HER2/Neu Negative, HER2/Neu Negative, HER2/Neu Negative, HER2/Neu Negative, HER2/Neu Negative, HER2/Neu Negative
Treatment laboratory biomarker analysis, Letrozole, Pembrolizumab, Palbociclib
Clinical Study IdentifierNCT02778685
SponsorCity of Hope Medical Center
Last Modified on19 February 2021


Yes No Not Sure

Inclusion Criteria

Willing and able to provide written informed consent/assent for the trial
Willing and able to comply with all aspects of the treatment protocol
Postmenopausal women defined by at least one of the following criteria
Prior bilateral oophorectomy OR amenorrheic for >= 12 months (if =< 55 years of age and prior to chemotherapy, or on medical ovarian ablative therapy, OR
Previous hysterectomy with one or both ovaries left in place (previous hysterectomy in which documentation of bilateral oophorectomy is unavailable AND FSH values consistent with the institutional normal values for the post-menopausal state; FSH levels must be obtained within 28 days prior to registration)
Presence of measurable disease meeting the following criteria: at least 1 lesion of > 10 mm in long axis diameter for non-lymph nodes or > 15 mm in short axis diameter for lymph nodes that is serially measurable according to RECIST version 1.1 using computerized tomography, magnetic resonance imaging, or panoramic and close-up color photography
Newly diagnosed (cohort 2) stage IV metastatic ER+HER2- breast cancer histologically proven per current American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) guidelines; allow up to 30 days prior use of CDK4/6 inhibitors and up to 60 days of letrozole for treatment of metastatic ER+ breast cancer
Life expectancy of >= 3 months
Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 0-2
Willing to provide tissue from a newly obtained core or excisional biopsy of a tumor lesion; newly-obtained is defined as a specimen obtained up-to 6 weeks (42 days) prior to initiation of treatment on day 1; subjects for whom newly-obtained samples cannot be provided (e.g. inaccessible or subject safety concern) may submit an archived specimen only upon agreement from the study principal investigator (PI)
Absolute neutrophil count (ANC) >= 1,000 /mcL
Platelets >= 100,000 /mcL
Hemoglobin >= 9 g/dL or >= 5.6 mmol/L without transfusion or erythropoietin (EPO) dependency (within 7 days of assessment)
Serum creatinine =< 1.5 X upper limit of normal (ULN) OR measured or calculated creatinine clearance (glomerular filtration rate [GFR] can also be used in place of creatinine or creatinine clearance [CrCl]) >= 60 mL/min for subject with creatinine levels > 1.5 x institutional ULN
Serum total bilirubin =< 1.5 X ULN OR direct bilirubin =< ULN for subjects with total bilirubin levels > 1.5 ULN
Aspartate aminotransferase (AST) (serum glutamic-oxaloacetic transaminase [SGOT]) and alanine aminotransferase (serum glutamate pyruvate transaminase [SGPT]) =< 2.5 X ULN OR =< 5 X ULN for subjects with liver metastases
Albumin >= 2.5 mg/dL
International normalized ratio (INR) or prothrombin time (PT) =< 1.5 X ULN unless subject is receiving anticoagulant therapy as long as PT or partial thromboplastin time (PTT) is within therapeutic range of intended use of anticoagulants
Activated partial thromboplastin time (aPTT) =< 1.5 X ULN unless subject is receiving anticoagulant therapy as along as PT or PTT is within therapeutic range of intended use of anticoagulants
Female subjects of childbearing potential should have a negative urine or serum pregnancy within 72 hours prior to receiving the first dose of study medication; if the urine test is positive or cannot be confirmed as negative, a serum pregnancy test will be required
Female subjects of childbearing potential should be willing to use two methods of birth control or be surgically sterile, or abstain from heterosexual activity for the course of the study through 120 days after the last dose of study medication; subjects of childbearing potential are those who have not been surgically sterilized or have not been free from menses for > 1 year
Cohort 1 (accrual to 6 patients) is for patients who had ongoing stable disease (SD) on letrozole + palbociclib, enrolled on prior version of eligibility criteria to receive pembrolizumab after obtaining stable disease on letrozole + palbociclib; these patients must have been on treatment with letrozole and palbociclib for 6 months with SD per RECIST 1.1; received up to 3 lines of previous therapy including endocrine and/or chemotherapy in advanced setting prior to initiation of letrozole and palbociclib; no grade 3 toxicities except alopecia

Exclusion Criteria

Patients currently participating and receiving study therapy or who have participated in a study of an investigational agent and received study therapy or used and investigational device within 4 weeks of the first dose of treatment
Previously received pembrolizumab or other anti-programmed cell death-1 (PD-1) or anti-PD-L1 immunotherapy
Does not have measurable disease per RECIST 1.1
For cohort 2, received > 30 days of prior treatment with endocrine therapy +/- CDK4/6 inhibitors before screening (letrozole is allowed for prior adjuvant endocrine therapy)
Diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other form of immunosuppressive therapy within 7 days prior to the first dose of trial treatment
Known history of active TB (Bacillus tuberculosis)
Hypersensitivity to pembrolizumab or any of its excipients
Prior anti-cancer monoclonal antibody (mAb) within 4 weeks prior to study day 1 or has not recovered (i.e., =< grade 1 or at baseline) for adverse events (AEs) due to agents administered > 4 weeks earlier
Prior chemotherapy, targeted small molecule therapy, or radiation therapy within 2 weeks prior to stay day 1 or has not recovered (i.e. =< grade 1 or at baseline) from AEs due to a previously administered agent
Note: Patients with =< grade 2 neuropathy are an exception to this criterion and may qualify for the study
Note: If patient received major surgery, she must have recovered adequately from the toxicity and/or complications from the intervention prior to starting therapy
Known additional malignancy that is progressing or requires active treatment; exceptions include basal cell carcinoma of the skin or squamous cell carcinoma of the skin that has undergone potentially curative therapy or in situ cervical cancer
Known active central nervous system (CNS) metastases and/or carcinomatous meningitis; patients with previously treated brain metastases may participate provided they are stable (without evidence of progression by imaging for at least 4 weeks prior to the first dose of trial treatment and any neurologic symptoms have returned to baseline), have no evidence of new or enlarging brain metastases, and are not using steroids for at least 7 days prior to trial treatment; this exception does not include carcinomatous meningitis, which is excluded regardless of clinical stability
Active autoimmune disease that has required systemic treatment in the past 2 years (i.e., with use of disease modifying agents, corticosteroids, or immunosuppressive drugs); replacement therapy (e.g., thyroxine, insulin, or physiologic corticosteroid replacement therapy for adrenal or pituitary insufficiency, etc.) is not considered a form of systemic treatment
History of (non-infectious) pneumonitis that required steroids or current pneumonitis
History of interstitial lung disease
Clinically active diverticulitis, intra-abdominal abscess, gastrointestinal (GI) obstruction, or abdominal carcinomatosis (known risks factors for bowel perforation)
Active infection requiring systemic therapy
History of significant cardiovascular disease, defined as: congestive heart failure greater than New York Heart Association (NYHA) class II according to the NYHA functional classification; unstable angina or myocardial infarction within 6 months of enrollment; or serious cardiac arrhythmia
Clinically significant electrocardiogram (ECG) abnormality, including a marked baseline prolonged QT/corrected QT (QTc) ([QT interval/corrected QT interval], e.g., a repeated demonstration of a QTc interval > 480 ms), a family or personal history of long or short QT syndrome, Brugada syndrome or known history of QTc prolongation, or Torsade de Pointes (TdP)
Concurrent use of drugs that are known to be moderate or strong cytochrome P450, family 3, subfamily A (CYP3A) inhibitors or inducers or drugs that are known to prolong the QT interval
History or current evidence of any condition, therapy, or laboratory abnormality that might confound the results of the trial, interfere with the patient's participation for the full duration of the trial, or is not in the best interests of the patient to participate, in the opinion of the treating investigator
Pregnant or breastfeeding, or expecting to conceive children within the projected duration of the trial, starting with the pre-screening or screening visit through 120 days after the last dose of trial treatment
Known psychiatric or substance abuse disorders that would interfere with cooperation with the requirements of the trial
Known history of human immunodeficiency virus (HIV) (HIV 1/2 antibodies)
Known active hepatitis B (e.g., hepatitis B surface antigen [HBsAg] reactive) or hepatitis C (e.g., hepatitis C virus [HCV] ribonucleic acid [RNA] [qualitative] is detected)
Received a live vaccine within 30 days of planned start of study therapy; Note: Seasonal influenza vaccines for injection are generally inactivated flu vaccines and are allowed; however intranasal influenza vaccines (e.g., Flu-Mist) are live attenuated vaccines, and are not allowed
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