Does obesity influence how breast cancer patients will benefit from further hormonal therapy?

This article investigated whether the body mass index or BMI (defined as weight divided by the square of height) can be used to determine how a patient with breast cancer treated with hormonal therapy may benefit from further treatment with a type of hormonal therapy called aromatase inhibitors.

Aromatase inhibitors such as anastrozole (Arimidex), exemestane (Aromasin), letrozole (Femara) are a type of hormonal therapy used for the treatment of postmenopausal (after menopause) women with hormone-positive breast cancer. Hormone-positive breast cancer is a type of breast cancer caused by estrogen, the main female sex hormone. Aromatase inhibitors work by blocking the protein aromatase, which normally helps the body make estrogens. Therefore, these drugs stop the production of estrogen, thus less hormones will be available to stimulate the growth of breast cancer cells. Obesity (defined as a BMI of 30kg/m2 or higher) is known to influence the outcomes of breast cancer patients. Also, it has been recently suggested that overweight (BMI between 25 and 29.9kg/m2) and obese patients may have less benefits from aromatase inhibitors than normal weight patients. The aim of this study was to investigate whether the BMI of breast cancer patients treated with hormonal therapy could predict their long-term benefit from further treatment with an aromatase inhibitor. 

Data for this study was collected from a group of patients who had taken part in an earlier trial which was published in 2007. 634 postmenopausal breast cancer patients who did not have a recurrence (return of the cancer) after 5 years of hormonal therapy (tamoxifen) were included in this study. Of these patients, 28% had normal weight, 48% were overweight and 24% were obese. 294 of all patients received further hormonal therapy using anastrozole for 3 years and 340 patients were the control group and did not receive any further medication. 

Results showed that normal weight patients who received 3 years anastrozole had a 52% and 55% lower risk of recurrence and death, respectively compared to normal weight patients with no further treatment. In addition, they had a 78% lower risk of developing distant metastases (cancer spread to distant organs of the body). However, overweight and obese patients had no significant benefit from further anastrozole treatment, with only a 7% lower risk of recurrence and a 9% lower risk of developing distant metastases. 

In summary, this study showed that a higher BMI can predict smaller benefits from further hormonal therapy with aromatase inhibitors in postmenopausal breast cancer patients. 

This was a retrospective study (it looked at patients who had been treated in the past rather than following them throughout their treatment and determining their outcomes). This type of study is considered to provide weaker statistical information.

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