ERBB2 and breast cancer: The purpose of this study is to evaluate the content validity of the National Comprehensive Cancer Network – Functional Assessment of Cancer Therapy – Breast Cancer Symptom Index (NFBSI-16) and the Patient-Reported Outcomes Measurement Information System (PROMIS) Physical Function Short Form 10b among patients with hormone receptor positive (HR+)/human epidermal growth factor receptor 2 negative (HER2-) advanced breast cancer.