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Clinician’s Corner: Treatment of Breast Cancer

For the month of October our focus is on breast cancer its diagnosis and prevention.  This week we discuss our role of your Thompson Pharmacist in the treatment with drug therapy.  Here is a brief review of the two main classes of drug therapy, along with counseling points for those therapies that your pharmacist wants you to know.

Role of Anti-Estrogens: (SELECTIVE ESTROGEN RECEPTOR MODULATORS)

For breast cancer that is estrogen receptor positive, ANTI-Estrogens are the mainstay of treatment.  Antiestrogens bind to estrogen receptors and prevent receptor mediated gene transcription, and are therefore used to block the effect of estrogen on the end target. 70-75% of Breast cancer tumors are estrogen receptor positive.

Nolvadex® (tamoxifen): blocks the estrogen receptor and is considered first line therapy of estrogen receptor positive breast cancer. Tamoxifen is the only “anti-estrogen” that can be used before or after menopause.

Evista® (raloxifene) Available as tablets: 60mg

Dosage: 60mg once daily

Indications:  Reduction in risk of invasive breast cancer in postmenopausal women with

Osteoporosis OR if at high risk for invasive breast cancer. Binds to estrogen receptors in the breast.

Side effects: Watch for blood clots. May cause hot flashes, muscle aches & pains.

Efficacy: seems to be less effective than Tamoxifen for breast cancer treatment.

ROLE of Aromatase Inhibitors for prevention of Breast Cancer

An enzyme called aromatase is responsible for forming estrogen outside of the ovaries.  Blocking aromatase blocks formation of estrogen, that can bind to the breast. Indicated only for post-menopausal women.

Side effects: hot flashes, infrequent vaginal bleeding, do not predispose to endometrial cancer.  All these drugs are available generically and are rather inexpensive therapies.

  • Arimidex® (anastrozole) available as 1mg tablets dosed once daily.
  • Femara® (letrozole) available as 2.5mg tables dosed once daily.
  • Aromasin® (exemestane) available as 25mg tablets dosed once daily after a meal

COUNSELING POINTS for BREAST CANCER DRUG TREATMENT

  • Drug therapy is used following surgery & radiation to “clean up” cancer cells that may have spread beyond breast
  • Goal of hormonal therapy is block estrogen’s growth promoting effect. Continue anti-estrogen therapy for 5 years—make sure you don’t miss doses of your medication.
  • Tamoxifen and aromatase inhibitors are first line. Remember that only tamoxifen can be used in pre-menopausal women.
  • Hot flashes are most common side effect.
  • Some antidepressants like Prozac and Paxil block the effect of tamoxifen.
  • Aromatase inhibitors cause fewer hot flashes that Tamoxifen.
  • KNOW the symptoms of blood clots:
    • Shortness of breath
    • Chest pains worsen with breathing or coughing.
    • Coughing up blood
    • Pain, tenderness, swelling, warmth, redness in one leg
  • Aromatase inhibitors may cause significant bone loss.  Osteoporosis and fractures have been reported. Treat accordingly- drugs like Alendronate (Fosamax®) are a good choice.