Sarcopenia, or low muscle mass, occurs in more than one-third of newly diagnosed nonmetastatic breast cancer patients and is associated with higher overall mortality, according to a new study in JAMA Oncology.

“The importance of body size on cancer outcomes is of great clinical interest,” wrote author Bette J. Caan, DrPH, division of research at Kaiser Permanente in Oakland, California, and colleagues. “Measures of body composition that can distinguish adipose tissue distribution, as well as the quantity and quality of muscle, can help refine our understanding of body size to cancer survival.”

The authors studied data taken from CT scans of more than 3,000 women diagnosed with stages II or III breast cancer from January 2000 to December 2013. The median age of the women was 54. Thirty-four patients presented with sarcopenia, while 37 percent presented with low muscle radiodensity.

Overall, among patients with nonmetastatic breast cancer, patients with sarcopenia had higher overall mortality than those without sarcopenia. Patients in the highest tertile of total adipose tissue (TAT) had higher overall mortality than those in the two lowest tertiles. No association with survival was found for low muscle radiodensity.  

“We demonstrate that sarcopenia is not a condition restricted to patients with later-stage disease but rather is highly prevalent among patients with nonmetastatic disease across all levels of BMI,” the authors wrote. “Our findings are likely generalizable across many other nonmetastatic cancers because the associations with muscle and improved survival for those with metastatic cancer has been observed across a variety of solid tumors.”

Caan et al. noted that body mass index (BMI) is “the most common measure of body size, and the relationship between obesity and breast cancer survival has been widely studied.” Their findings, however, suggest that BMI may not be the most effective way to study breast cancer survival.

“BMI alone was not significantly related to overall mortality and did not appropriately identify patients at risk of death owing to their body composition,” the authors wrote.