Inavolisib (Itovebi – Genentech), an oral kinase inhibitor, has been approved by the FDA for use in combination with palbociclib and fulvestrant for treatment of endocrine-resistant, PIK3CA-mutated, hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative, locally advanced or metastatic breast cancer. This is the first approval for Itovebi; palbociclib and fulvestrant have been available for years for treatment of HR-positive, HER2-negative breast cancer.

The oral kinase inhibitor capivasertib (Truqap – AstraZeneca), a first-in-class AKT inhibitor, has been approved by the FDA for use in combination with the selective estrogen receptor degrader (SERD) fulvestrant (Faslodex, and generics) for treatment of hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative, locally advanced or metastatic breast cancer in adults with one or more PIK3CA/AKT1/PTEN-alterations who had disease progression on at least one endocrine-based regimen for metastatic disease or recurrence on or within 12 months of completing adjuvant therapy.

The oral cyclin-dependent kinase (CDK) 4/6 inhibitor abemaciclib (Verzenio – Lilly) has been approved by the FDA for use in combination with endocrine therapy (tamoxifen or an aromatase inhibitor) for adjuvant treatment of patients with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative, node-positive, early breast cancer at high risk of recurrence.1It was previously approved for the same indication, but patients were also required to have a Ki-67 score ≥20%. About 70% of all breast cancers are HR-positive and HER2-negative. Ki-67 is a prognostic biomarker for tumor proliferation; a score ≥20% is associated with early recurrence and poor prognosis.

The FDA has approved elacestrant (Orserdu – Stemline), an oral estrogen receptor antagonist, for treatment of estrogen receptor (ER)-positive, human epidermal growth factor receptor 2 (HER2)-negative, estrogen receptor 1 (ESR1)-mutated advanced or metastatic breast cancer in postmenopausal women or men who had disease progression following endocrine therapy. Elacestrant is the first oral selective estrogen receptor degrader (SERD) to be approved for treatment of breast cancer; the injectable SERD fulvestrant (Faslodex, and generics) was approved more than 20 years ago.

The FDA has approved abemaciclib (Verzenio – Lilly), an oral cyclin-dependent kinase (CDK) 4/6 inhibitor, for treatment of hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced or metastatic breast cancer. Abemaciclib is the third CDK 4/6 inhibitor to be approved in the US for this indication.

The oral cyclin-dependent kinase (CDK) 4/6 inhibitor ribociclib (Kisqali – Novartis) has been approved by the FDA for use in combination with an aromatase inhibitor for first-line endocrine-based therapy in postmenopausal women with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced or metastatic breast cancer. Ribociclib is also available copackaged with the aromatase inhibitor letrozole (Femara, and generics) as Kisqali Femara Co-Pack. Ribociclib is the second CDK 4/6 inhibitor to be approved in the US for this indication; palbociclib (Ibrance) was the first. Abemaciclib (Verzenio), a third CDK 4/6 inhibitor, was recently approved and will be reviewed in a future issue.

Palbociclib (Ibrance – Pfizer), an oral cyclin-dependent kinase inhibitor, has been approved by the FDA for use in combination with the aromatase inhibitor letrozole (Femara, and generics) for first-line treatment of postmenopausal women with estrogen receptor (ER)-positive, human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer. It is the first cyclin-dependent kinase inhibitor to become available in the US.

In addition to surgery and radiation therapy, a variety of drugs are used both singly and in combination to treat breast cancer. This article summarizes the principles of adjuvant therapy and treatment for metastatic disease. A summary of individual drugs and their adverse effects begins on page 3.

The tables in this article list drugs used for treatment of cancer in the USA and Canada and their major adverse effects. The choice of drugs in Table I is based on the opinions of Medical Letter consultants. Some drugs are listed for indications for which they have not been approved by the US Food and Drug Administration. In some cases, such as elderly patients or those with many co-morbid illnesses, the regimen of choice might not be suitable. For many of the cancers listed, surgery and/or radiation therapy may be the treatment of choice or may also be part of the management. Anticancer drugs and their adverse effects are listed in Table II on page 46. A partial list of brand names appears on page 52.

Fulvestrant (Faslodex -- AstraZeneca), an estrogen receptor antagonist given intramuscularly (IM) once a month, was recently approved by the FDA for treatment of hormone-receptor-positive metastatic breast cancer in postmenopausal women with disease progession on tamoxifen (Nolvadex, and others) or another antiestrogen.