Evaluating the Use of a Medication 'Switch' vs Guideline-directed Interventions for Relieving Side Effects of Aromatase Inhibitors Among Breast Cancer Patients

Inclusion Criteria:

* Histologic documentation of DCIS or invasive breast cancer by core needle or incisional biopsy.
* The DCIS or invasive cancer must be estrogen receptor alpha (ER)-positive
* The invasive cancer must be HER2-negative (IHC 0-1+, or with a FISH ratio of \<1.8 if IHC is 2+ or if IHC has not been done)
* Clinical Stage I-III invasive breast cancer or DCIS
* Patients for whom adjuvant treatment with one of the following would be clinically indicated: letrozole, anastrozole, exemestane
* Patients who anticipate continuing with adjuvant endocrine therapy for a minimum of 2 years at the time of registration
* Women over 18 years of age who are post-menopausal, defined as last menstrual period \>2 years prior to registration, or \>1 year prior to registration with FSH and estradiol in post-menopausal range.
* Patients must meet the following clinical laboratory criteria:

  * Absolute neutrophil count (ANC) \>1,000/mm3 and platelet count \> 75,000/mm3
  * Total bilirubin \<1.5 x the upper limit of the normal range (ULN).
  * Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) \< 3 x ULN.
* Ability to give informed consent.

Exclusion Criteria:

* Prior endocrine therapy for any histologically-confirmed cancer or prevention of breast cancer in the last 10 years is not allowed.
* Any other adjuvant therapy for breast cancer. Exception: Bisphosphonate or denosumab treatment for metabolic bone issues are allowed.
* Patients who are prescribed tamoxifen as the first endocrine therapy rather than an aromatase inhibitor.
* Women who are pregnant or lactating.
* Prisoners.