An observational study in Advanced Breast Carcinoma, Locally Advanced Breast Carcinoma and Metastatic Breast Carcinoma, sponsored by Mayo Clinic. Active, not recruiting at 3 sites in United States. Open to female participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2026-06-09.
Sponsored by Mayo Clinic · Observational
This research trial studies genetic profiles in blood and tumor samples from patients with estrogen receptor positive and HER2 negative breast cancer that has spread to other places in the body who are receiving palbociclib and endocrine therapy. Examining the genetic changes associated with the cancer and comparing the genetic material from the cancer tissue with the genetic material found in the blood may help doctors to develop customized treatment for breast cancer.
Women who have disease that is amenable to biopsy and agree to undergo a standard of care core biopsy of recurrent or metastatic breast cancer, and to collect additional core samples for research purposes
PRE-REGISTRATION INCLUSION CRITERIA
Women who have disease that is amenable to biopsy and agree to undergo a standard of care and /or research biopsy
Patients must satisfy one of the following criteria for prior therapy:
Second line therapy setting only: The intention to begin palbociclib and fulvestrant as treatment for metastatic breast cancer (after progression on first line endocrine therapy)
Measurable disease as defined by Response Evaluation Criteria in Solid Tumors (RECIST) criteria or bone only disease are eligible.
Women who are premenopausal must agree to begin or continue an leutinizing hormone releasing hormone (LHRH) agonist (goserelin preferred)
REGISTRATION INCLUSION CRITERIA
Histologic confirmation from the pre-registration biopsy of either locally advanced or metastatic breast cancer that is ER-positive and HER2 -negative
Note: ER-positive disease is defined as >= 10% nuclear staining; HER2-negative disease per American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) guidelines, one of the following must apply:
Exclusion Criteria:
PRE-REGISTRATION EXCLUSION CRITERIA
Uncontrolled intercurrent illness including, but not limited to:
REGISTRATION EXCLUSION CRITERIA
Any of the following therapies prior to registration:
Monoclonal antibodies =\< 2 weeks
Radiation therapy =\< 2 weeks
The following patients are not eligible
Patents undergo collection of blood and stool samples at baseline, 7 days after letrozole monotherapy treatment, and at completion of each cycle, urine samples at baseline and completion of each cycle, and saliva samples at baseline. Patients also undergo collection of blood and urine samples at disease progression. Biopsy samples are analyzed for genetic profile via genome sequencing and RNA sequencing. Biopsy samples are also used for the generation of xenograft mice model.
Procedure: Biopsy · Procedure: Biospecimen Collection · Other: Laboratory Biomarker Analysis
Undergo tumor biopsy
Also known as: BIOPSY_TYPE, Bx
Undergo collection of blood, urine, stool, and saliva
Correlative studies
Bioinformatics analysis
Next-generation sequencing data will be used to identify variants associated with the progression free survival. Pathology analysis will also be performed.
Time frame: Up to 3 years
Ki67 and TK1 changes
Spearman rank correlation coefficients will be used to assess the relationship between tumor ki67 levels and serum TK1 levels prior to the start of treatment and after 2 months of treatment with palbocic.
Time frame: after 2 months of treatment
Changes in EMT markers (including Vimentin, SLUG and E-cadherin) and tumor infiltrating lymphocytes (TILs) (including CD8, PD-L1, and FOXP3)
Wilcoxon signed rank tests will be used to assess the fold changes in EMT and TILs after 2 cycles of treatment. Benjamini-Hochberg procedure will be used to control false postive rate.
Time frame: after 2 months of treatment
Changes in serum TK1 levels
Wilcoxon rank sum tests will be used to assess whether a given element of the CD44high/CD24/low/estrogen receptor (ER) low cancer stem cell-like phenotype differ between those whose TK1 levels fell below 200 after 2 cycles of treatment and those whose TK1 levels remained above 200 after 2 cycles of treatment.
Time frame: After 2 months of treatment
Change in phenotype of Ki67 and serum TK1 levels
The parameter estimates from fitting a univariate Cox model to these data will be used to obtain an estimate of the hazard ratio and its corresponding 95% confidence interval.
Time frame: After 2 months of treatment
Differences between those with and without a blood draw taken
A Wilcoxon rank sum test will be used to assess whether baseline TK1 levels differ among those who discontinue treatment prior to the 2 month blood draw and those who do not.
Time frame: After 2 months of treatment
This study is active, not recruiting, as verified in Jun 2026. You cannot join it, but the record below documents what was studied.
Get an email when the registry record changes — status, dates, results — or when someone posts here.
Sign in to followQuestions and observations about this study, from anyone following it. Not medical advice, and not a channel to the study team — their contact details are on the registry record.
Sign in to join the discussion. Reading takes no account; posting does. You choose a display name, and a pseudonym is the default.
Nothing here yet. If you are running this trial, taking part in it, or weighing whether to, this is the place to say so.
Mayo Clinic