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.

Interim results of a double-blind, placebo-controlled trial suggest that off-label use of the anticholinergic drug oxybutynin may reduce the frequency and severity of hot flashes in women with breast cancer. Extended-release oral oxybutynin (Ditropan XL, and generics) has been shown to reduce the frequency and severity of hot flashes in healthy menopausal women.

The FDA has approved a low-dose formulation of the selective serotonin reuptake inhibitor (SSRI) paroxetine mesylate (Brisdelle – Noven Therapeutics) for treatment of moderate-to-severe vasomotor symptoms associated with menopause. It is the first non-hormonal therapy to be approved for this indication. Paroxetine mesylate (Pexeva) and paroxetine hydrochloride (Paxil, and generics) are marketed in higher doses for treatment of depression and other psychiatric disorders.

The FDA has approved ospemifene (os pem’ i feen; Osphena – Shionogi), an estrogen agonist/antagonist, for oral treatment of moderate to severe dyspareunia in postmenopausal women. Ospemifene is the fourth estrogen agonist/antagonist to be marketed in the US, but it is the only one that has an estrogen-like effect on vaginal epithelium. The other three, tamoxifen (Nolvadex, and generics), toremifene (Fareston), and raloxifene (Evista), are used for treatment and prevention of breast cancer and osteoporosis.

Adjuvant hormone therapy with anti-estrogen drugs has been shown to reduce disease recurrence and mortality in postmenopausal women with estrogen receptor (ER)-positive breast cancer. In recent years, aromatase inhibitors (AI) have become the preferred first-line hormonal treatment over tamoxifen for such patients.1,2

Use of a selective serotonin reuptake inhibitor (SSRI) is common in women taking tamoxifen (Nolvadex, and others) for breast cancer, both to treat depression and to decrease hot flashes. However, tamoxifen must be metabolized by CYP2D6 to become pharmacologically fully active (MJ Higgins et al. J Natl Compr Canc Netw 2009; 7:203), and the SSRIs fluoxetine (Prozac, and others) and paroxetine (Paxil, and others) are strong inhibitors of CYP2D6. Sertraline (Zoloft, and others) inhibits CYP2D6 to a lesser extent. Citalopram (Celexa, and others) and escitalopram (Lexapro), the 2 other SSRIs approved for treatment of depression, are only weak inhibitors of CYP2D6.

Two observational studies presented at a recent meeting of the American Society of Clinical Oncology (45th annual meeting, May 29-June 2, 2009, Orlando, FL abstracts CRA508, CRA509) examined the effect of strong inhibitors of CYP2D6 on the success rate of tamoxifen in preventing recurrence of breast cancer. One found that women who took fluoxetine, paroxetine or sertraline (or bupropion, duloxetine, terbinafine, quinidine or long-term diphenhydramine) with tamoxifen had a higher 2-year recurrence rate (13.9% vs. 7.5%). The other study found no association between cancer recurrence and use of a CYP2D6 inhibitor.

There is no good evidence that any one SSRI is more effective than any other for treatment of depression. For women who are taking tamoxifen and need to begin treatment with an SSRI to treat depression, citalopram or escitalopram might be the safest choice (Treat Guidel Med Lett 2006; 4:35). Use of an SSRI to treat hot flashes in women taking tamoxifen should probably be reconsidered.

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Preliminary results from a new study, unpublished but reported in a press release from the National Cancer Institute and widely disseminated in the public press, suggest that raloxifene (Evista) might be a better choice than tamoxifen (Nolvadex, and others) for prevention of breast cancer in high-risk postmenopausal women.

Serious adverse interactions between drugs continue to be reported. Many of these are due to inhibition or induction of cytochrome P450 (CYP) enzymes, particularly CYP3A4. CYP3A is thought to be involved in the metabolism of more than 50 percent of currently prescribed drugs.2 CYP3A4, which is more abundantly expressed than CYP3A5, accounts for most CYP3A activity in vivo.

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.

Changes caused by one drug in the absorption, distribution, metabolism or excretion of another may lead to a pharmacokinetic adverse drug interaction (DN Juurlink et al, JAMA 2003; 289:1652). Additive drug interactions, such as vasodilation caused by both sildenafil (Viagra) and nitrates, can also have adverse effects.

Anastrozole (Arimidex - AstraZeneca, Medical Letter 1996; 38:61), an aromatase inhibitor, has received accelerated approval from the FDA for adjuvant treatment of postmenopausal women with early hormone-receptor-positive breast cancer. The drug was approved for treatment of postmenopausal women with metastatic breast cancer in 1996.

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.

Many drugs are now marketed for prevention and treatment of postmenopausal osteoporosis. All regimens should include an adequate intake of calcium and vitamin D.

The FDA has approved exemestane, an aromatase inhibitor, for the treatment of postmenopausal women with advanced breast cancer that has progressed during treatment with tamoxifen.

Reports of adverse interactions between drugs continue to accumulate. Recently, the FDA has expanded the recommendations on drug interactions found in the package inserts of new drugs.

Clopidogrel bisulfate (Plavix - Bristol-Myers Squibb/Sanofi), a new thienopyridine antiplatelet agent similar to ticlopidine (Ticlid - Medical Letter, 34:65, 1992), has been approved by the US Food and Drug Administration (FDA) for secondary prevention of myocardial infarction, stroke and other vascular events.

Raloxifene (Evista - Lilly), a benzothiophene that acts on estrogen receptors, has recently been marketed for prevention of postmenopausal osteoporosis. Only estrogen (alone or in combination with a progestin) and the bisphosphonate alendronate (Fosamax) were previously approved by the FDA for this indication.

Anastrozole (Arimidex - Zeneca), a selective nonsteroidal aromatase inhibitor, has been approved by the US Food and Drug Administration (FDA) for treatment of postmenopausal women with advanced breast cancer that has progressed during treatment with tamoxifen (Nolvadex, and others).

The bone mass of an average person reaches a maximum at the age of 25 to 30, stays the same for about 15 years, and then progressively declines at a rate of 0.2% to 0.5% per year. At menopause, women go through a period of increased bone resorption (2% per year) for about 10 years and then resume a gradual rate of bone loss. Current strategies for prevention and treatment of Postmenopausal Osteoporosis include increasing calcium intake to maximize peak bone mass, using antiresorptive drugs to decrease postmenopausal resorption, and using other drugs to stimulate bone systhesis (BL Riggs and LJ Melton, III, N Engl J Med, 327:620, Aug 27, 1992).

The most important prognostic variable in early breast cancer is axillary lymph node involvement. Based on past experience, after 10 years about 70% of node-negative patients will be alive and apparently free of disease; about 30% will have relapsed or died. Patients with positive nodes may have a 30% to 60% relapse rate, depending on the number of positive nodes and other prognostic factors, such as the presence of estrogen receptors (IC Henderson et al, in VT DeVita, Jr et al, eds, Cancer: Principles and Practice of Oncology, 3rd ed, Philadelphia:Lippincott, 1989, p 1197). Which of these patients should receive adjuvant treatment with cytotoxic drugs and/or endocrine therapy is controversial; a National Cancer Institute (NCI) Consensus Conference on this subject is scheduled for June.