What muscle has to do with breast cancer survival

  09 April 2018    Read: 856
What muscle has to do with breast cancer survival

Want more evidence that muscles are good? Not mussels, as in the shellfish often served with garlic and wine, but muscles, as in strong. Well, a study published in JAMA Oncology found that women with low muscle mass were significantly less likely to survive Stage 2 or 3 breast cancer.

For the study, a team of researchers specifically compared patients who had sarcopenia when they were diagnosed with Stage 2 or 3 breast cancer versus those who did not. Sarcopenia may sound a brand of raunchy sarcasm but in medical-speak, "sarco" means "muscle" and "penia" means "lack or deficiency." Therefore, sarcopenia means "muscle lack" or "muscle deficiency." As a National Institutes of Health (NIH) website describes, many types of cancer can lead to loss of muscle through mechanisms that are not yet clear. Stage 2 or 3 breast cancer is cancer that is growing but still has not spread to parts of the body distant from the breast.

Here's how the team from Kaiser Permanente, the University of Alberta, Canada, and the Dana Farber Cancer Institute conducted the study. They reviewed the records of 3241 women who were initially diagnosed at Kaiser Permanente of Northern California or Dana Farber Cancer Institute sometime from January 2000 to December 2013. All had received CT (computerized tomography) scans of their abdomens around the time of their breast cancer diagnoses that then allowed the researchers to determine if they had sarcopenia and estimate the amount of fat in their bodies. (Muscle and fat look quite different on a CT scan with fat looking darker and muscle appearing brighter.)

For the study, the researchers defined sarcopenia as having a skeletal muscle index of less than 40. To calculate this index, they looked specifically at the CT cross section of the abdomen at the level of the patient's third lumbar vertebra (which is at the lower back). The skeletal muscle index is the area of the cross section that is occupied by muscle in square centimeters divided by the height of the cross section in meters squared. Previous studies had shown that the amount of muscle at this cross section of the body tends to correlate with the amount of muscle elsewhere in the body (assuming that the person does not have an excessively muscular or non-muscular abdomen).

The researchers then reviewed each patient's medical records for as long as the patient was followed (a median of 6 years) to determine whether she had subsequently survived.

The main finding: having less muscle and more fat was bad. About a third of the patients (34%) had sarcopenia on their first CT. Those who had sarcopenia were 41% more likely to have subsequently died than those who did not. Those who were in the top third in amount of fat were 35% more likely to have died than those who were in the lowest third. Patients with both sarcopenia and a high amount of fat in the body were 89% more likely to have died.



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