Tolerability of Therapies Recommended for the Treatment of Hormone Receptor-Positive Locally Advanced or Metastatic Breast Cancer

For women with hormone receptor-positive advanced breast cancer, endocrine therapies, including the selective estrogen receptor modulator tamoxifen, the aromatase inhibitors anastrozole, letrozole, and exemestane, and the selective estrogen receptor degrader fulvestrant, are recommended in clinical guidelines. The addition of targeted agents such as everolimus or palbociclib to aromatase inhibitors are also recommended as treatment options. Chemotherapy remains an option, although clinical guidelines have recommended these agents be reserved for patients with immediately life-threatening disease or if resistance to endocrine therapy is known or suspected. The present review has consolidated the tolerability profiles of the agents approved for use in the treatment of hormone receptor-positive advanced or metastatic breast cancer based on phase III registration trial data. Endocrine therapies are generally well tolerated, although the addition of targeted therapies to aromatase inhibitors or fulvestrant appears to increase the proportion of patients experiencing adverse events, and palbociclib and chemotherapy appear to be more closely associated with serious adverse events, including neutropenia.