Study: Weight gain associated with breast cancer survivorship

IN-DEPTH REVIEW OF RESEARCH

Study background:

Many studies have noted weight gain in breast cancer survivors, but they do not directly compare these women with women who have never been diagnosed with cancer.  Without the comparison, it is harder to see whether breast cancer survivors are actually gaining more weight or not. 

Researchers of this study wanted to know:

Whether breast cancer survivors with a family history of breast cancer gain more weight after their diagnosis compared to previvors.

Population(s) used in the study:  

The study compared 303 breast cancer survivors with 307 previvors who had not had breast cancer. All women had either a family history of breast or ovarian cancer, a BRCA1/2 mutation, or a diagnosis of early breast cancer (diagnosed at age 40 or younger). Participating breast cancer survivors had a personal history of breast cancer (DCIS or stage I-III breast cancer) that had been treated with surgery. The previvors included in the study were matched to the survivors based on age and menopausal status.  The breast cancer survivors in this study were further subdivided into two categories: survivors who had been diagnosed with breast cancer 5 years or less prior to the study start date, and survivors who had been diagnosed with breast cancer more than 5 years prior to the study start date. 

Study results:

• Overall, breast cancer survivors gained on average approximately 3 more pounds than previvors.
• When compared with other subtypes, breast cancer survivors who were diagnosed with ER-negative invasive breast cancer within the 5 years prior to the study start date had the greatest weight gain. This group gained on average approximately 7 more pounds than previvors.
• Premenopausal breast cancer survivors diagnosed with breast cancer within the 5 years prior to the study start date gained on average approximately 6 more pounds than premenopausal previvors.  
• Postmenopausal breast cancer survivors diagnosed with breast cancer within the 5 years prior to the study start date gained on average approximately 4 more pounds than postmenopausal previvors.
• Overall, breast cancer survivors who had received chemotherapy with or without hormone therapy gained on average approximately 4 pounds compared to previvors. An average weight gain of approximately 8 pounds was seen in breast cancer survivors treated with chemotherapy only.
• Compared to previvors, survivors who received chemotherapy were 2.1 times more likely to gain at least 11 pounds at the researchers’ follow-up point.

Limitations

The majority of the study population was white, which means that these findings might not apply to breast cancer survivors of other racial or ethnic backgrounds. Researchers also did not directly measure the women’s weights—they relied on self-reporting, which may not have been accurate.  Additionally, breast cancer survivors who did not have a family history of cancer were not included in the comparisons. 

Conclusion:

This is a highly relevant study for breast cancer survivors. It shows that in women with a family history of breast cancer and/or a mutation in a gene that increases cancer risk, breast cancer survivorship is a risk factor for weight gain. However, it is important to remember that this is only an association—the study does not show that the weight gain is caused by the breast cancer or the chemotherapy used to treat the breast cancer. More research is needed to find the exact cause, but the study’s authors note that the chemotherapy associated weight gain might be due to less physical activity or with changes in the patient’s metabolism. 

It is also important to note that the average overall weight gain in this study was approximately 3 pounds in breast cancer survivors. Currently we do not know whether gaining that amount increases risk of second primary cancer development or cancer recurrence. For comparison, a study done by Dr. Michelle Holmes’ research group found that women who gained between 0.5 and 2.0 kg/m2 (average weight gain of approximately 7 pounds) and women who gained more than 2.0 kg/m2 (average weight gain of approximately 20 pounds) had elevated risk of breast cancer death compared to women who maintained their weight.

In summary, there is an association between breast cancer and weight gain, and potential health problems are associated with weight gain. Researchers do not know the exact effect that gaining 3 pounds will have on breast cancer survivors. American Cancer Society guidelines say women should try to maintain their weight after a breast cancer diagnosis. 

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posted 8/24/15