Summary

This phase II trial studies how well radiation therapy given with standard care palbociclib and hormone therapy work in treating patients with breast cancer that has spread from one part of the body to the bone (bone metastasis). Radiation therapy uses high energy x-rays to kill tumor cells and shrink tumors. Palbociclib may stop the growth of tumor cells by blocking some of the enzymes needed for cell growth. Estrogen can cause the growth of breast cancer cells. Letrozole, anastrozole, and exemestane lowers the amount of estrogen made by the body. This may help stop the growth of tumor cells that need estrogen to grow. Fulvestrant and tamoxifen blocks the use of estrogen by the tumor cells. Giving radiation therapy, palbociclib, and hormone therapy may work better in treating breast cancer patients with bone metastasis.

Objectives

PRIMARY OBJECTIVE:
I. To evaluate the response rate three months post conventionally fractionated radiotherapy, relative to baseline, for bone metastases in breast cancer patients receiving concurrent palbociclib and hormone therapy treatment.

SECONDARY OBJECTIVES:
I. To determine whether conventionally fractionated radiotherapy in combination with palbociclib and hormone therapy in breast cancer patients with bone metastases adversely increases the frequency and severity of palbociclib toxicities including grade 3 neutropenia.
II. To determine whether radiotherapy in combination with palbociclib in breast cancer patients with bone metastases adversely increases the frequency and severity of radiotherapy toxicities including neurological and bone injury.
III. To assess fatigue, quality of life, and depression before and after radiotherapy for bone metastases in metastatic breast cancer patients treated with palbociclib.
IV. To determine progression free survival (PFS) and overall survival (OS) in breast cancer patients treated with palbociclib and concurrent radiotherapy to bone metastases.
V. To evaluate the relationship between volume of irradiated bone and side effects of treatment, including leukopenia and neutropenia.

TRANSLATIONAL RESEARCH OBJECTIVES:
I. To collect, store, and analyze circulating tumor-derived deoxyribonucleic acid (ctDNA) in metastatic breast cancer patients treated with palbociclib and radiotherapy to bone metastases and to determine the relationship between ctDNA and responders versus non-responders, PFS, and OS.
II. To collect, store, and analyze plasma for inflammatory cytokine measurements and determine their relationship with fatigue, depression, and quality of life before and after radiotherapy for bone metastases in metastatic breast cancer patients treated with palbociclib.
III. To collect, store, and analyze ribonucleic acid (RNA) for gene expression to identify functional biology processes over-represented in genes differentially regulated among patients who develop toxicities versus those who do not and those who are responders versus those who are not and to identify transcriptional regulatory pathways driving observed differences in gene expression.

OUTLINE:
Patients undergo radiation therapy over 5-10 days and receive palbociclib orally (PO) once daily (QD) on days 1-21. At the discretion of treating physician, patients also receive letrozole, anastrozole, exemestane, or tamoxifen PO QD on days 1-28, or fulvestrant intramuscularly (IM) on days 1 and 15 of cycle 1 and on day 1 of subsequent cycles. Cycles repeat every 28 days in the absence of disease progression or unacceptable toxicity.

After completion of study treatment, patients are followed up at 1 and 3 months.