Breast Cancer Drug Abandoned By 36% Of Patients Due To Side Effects

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36% of post-menopausal breast cancer patients who take aromatase inhibitors do not complete their treatment, because the drug’s side effects are so unpleasant, researchers from the Northwestern University Feinberg School of Medicine reported at the San Antonio Breast Cancer Symposium. Aromatase inhibitors are administered after chemotherapy, radiotherapy and breast cancer surgery, usually for about five years.

Lynne Wagner and team carried out a study involving 700 females who were on aromatase inhibitors. Within four years, 36% of them had dropped out of treatment because the side effects linked to them were unbearable. One in every ten patients abandoned treatment within 24 months.

Nasty (unbearable) side effects that cause the women to stop taking their medication included:

  • A drop in libido
  • Weight gain
  • Hot flashes (UK: hot flushes)
  • Severe pain in the joints

Those who had undergone radiation therapy or chemotherapy were more likely to stop taking their medication.

Professor Lynne Wagner said:

“If they had a rough time with chemo, if they’re feeling beaten up by treatment and medications, or if they’re the type of person who has difficulty tolerating side effects, then they’re much more likely to quit the drugs early.”


The researchers also found that what doctors perceived as side effects linked to the drugs were quite different in many ways, when compared to how patients described their experiences.

When previous studies had asked doctors about side effects associated with aromatase inhibitors, they reported that approximately 5% of patients had moderate to severe side effects. This figure is much lower than 36% who dropped out of treatment reported in this latest study – and did not count how many put up with the unpleasantness right to the end.

Wagner said:

“Now we’re appreciating that there’s a significant gap between patient-reported symptoms and provider-reported symptoms. That gap widens when we’re talking about more subjective symptoms, things like pain or fatigue that only a patient can report.”

Patients are often reluctant to be seen as difficult and bothersome, and many will not report unbearable side effects to their doctors. Busy doctors with a heavy schedule and full waiting rooms might not be spending enough time with each patient talking about this, the researchers added.

Aromatase inhibitors

Aromatase inhibitors, also known as AIs, are drugs used for breast and ovarian cancer treatment in postmenopausal patients. Off label, they may also be used to prevent breast enlargement (gynaecomastia) in males.

Ovarian and breast cancers need estrogen to grow. The enzyme aromatase synthesizes estrogen. Aromatase inhibitors do one of two things:

  • Undermine the production of estrogen. These are referred to as irreversible steroidal inhibitors. Aromasin (exemestane) is such a drug.
  • Block estrogen’s action on receptors. These are referred to as non-steroidal inhibitors. Arimidex (anastrozole) is an example of such a drug.

Arimidex
Arimidex (anastrozole) is an example of an aromatase inhibitor (Australian packaging)