Inclusion Criteria:

- Women 18 years and older with non-metastatic hormone receptor (ER and/or PR) positive
breast cancer who are eligible for and planning on starting treatment with an AI
within one month of signing consent.

- Postmenopausal, defined as at least one of the following: a) amenorrhea for at least
12 months b) prior bilateral oophorectomy at least 2 years prior to trial
registration.

Exclusion Criteria:

- History of autoimmune connective tissue disease, such as rheumatoid arthritis, lupus,
or other autoimmune conditions affecting joints.

- Treatment with steroid (for any condition, except for chemotherapy premedication)
within 30 days of trial registration.

- Prior treatment with an AI (patients previously or currently on tamoxifen are
eligible as long as patients are off tamoxifen for 2 weeks prior to baseline blood
draw)

- Active or ongoing infection

- Known metastatic disease

- Known history of HIV or hepatitis infections

- Ongoing radiation therapy (radiation must have been completed 2 weeks prior to
starting treatment with an AI)

- Non-invasive (DCIS, LCIS) cancer only (no diagnosis of invasive cancer)

- Pregnant or lactating

- Unable to speak, read, and write in English