Muscle Composition Metric May Help Predict Chemo Toxicity

Roxanne Nelson, BSN, RN

March 08, 2017

Measuring muscle composition may be able to help predict which patients will experience side effects from chemotherapy, as well as determining appropriate drug doses, according to new findings.

Dosing for chemotherapy dosing is typically based on the body surface area (BSA) formula, which accounts for a patient's height and weight but not other factors of body composition.

However, researchers found that the skeletal muscle gauge (SMG) a new and innovative metric developed at the University of North Carolina (UNC), Chapel Hill, was the best predictor of chemotherapy toxicity.

Through use of a combination of muscle mass (quantity) and radiodensity (quality), the SMG predicted adverse events, including grade 3 or 4 chemotherapy toxicities and hospitalizations.

The findings come from a study published online January 31 in Clinical Cancer Research.

Poor body composition metrics (BCM) have been associated with inferior cancer outcomes, and the authors note that increasing research has looked at sarcopenia and myopenia, among other body composition measures, by using computed tomography (CT).

"We looked at muscle mass on abdominal CT," said study author Hyman B. Muss, MD, Mary Jones Hudson Distinguished Professor and director of the UNC Lineberger Geriatric Oncology Program. "With computerized software we were able to compute the area of the muscle, then the areas of the abdominal section, and then get a measure of lean body mass."

"This has been verified with DEXA [dual-energy x-ray absorptiometry] scans," Dr Muss told Medscape Medical News. "Most people associate DEXA scans with bone density, but they can also look at muscle mass."

Good muscle, he explained, doesn't have a lot of fat, and a CT scan will show the amount of fat in muscle. Thus, it allows for gauging both quantity and quality of the muscle.

"We found that by looking primarily at the quality and to some degree the quantity, lean muscle mass was related to outcomes of chemotherapy and it is also a great overall measure of fitness," Dr Muss said.

Predicted Serious Adverse Events

In the current study, Dr Muss and colleagues calculated the BCM in 151 patients with early breast cancer (stage I to III) who had received neoadjuvant or adjuvant chemotherapy. All of the patients with human epidermal growth factor receptor 2 (HER2)–positive tumors had received concomitant anti-HER2 treatment with their chemotherapy.

Of this group, 50 women (33%) had developed grade 3 or 4 toxicities, but there were no associated deaths.

The authors analyzed existing abdominal CT scans for each patient in the cohort for skeletal muscle area, density, and fat tissue at the third lumbar vertebrae and calculated the skeletal muscle index and the SMG.

Overall, they found that poor BCM was significantly associated with a higher rate of treatment-related toxicities.

Even after adjustments for confounders such as age and body surface area, the authors found that low SMG (<1475 units) was significantly associated with both hematologic (relative risk [RR], 2.12; P = .02) and gastrointestinal grade 3 or 4 toxicities (RR, 6.49; P = .02), as well as hospitalizations (RR, 1.91; P = .05).

Additional Study in Larger Samples

Dr Muss noted that other researchers are also investigating this modality and that it "may be predictive of other functions and not just in cancer."

He is also hopeful that with more papers and large sample sizes, they will be able to see whether muscle mass is predictive of survival as well. Dr Muss and his team have completed another study that has not yet been published, in a larger population of patients with metastatic breast cancer.

"The patients received adjuvant therapy and we are showing similar numbers," he said. "We looked at the most aggressive therapy, and long-term data may show an effect on survival."

Very Promising, More Study Needed

Approached by Medscape Medical News for an independent comment, Tracey O'Connor, MD, associate professor in the Department of Medicine at Roswell Park Cancer Institute, Buffalo, New York, noted that this is an interesting study in patients with breast cancer examining a new metric.

"This metric clearly needs additional study but seems very promising as a method to identify patients at high risk for toxicity," said Dr O'Connor. "This study adds to the growing evidence that chemotherapy toxicity can be predicted by body composition."

"Because many cancer patients experience muscle loss, specific interventions to improve body composition may improve outcomes and help mitigate chemotherapy toxicity," she added.

Funded by the Friends of Rambam Medical Center, the J&G Zukier Medical Fund, and the Medical Student Training in Aging Research program of the American Federation for Aging Research. The authors have disclosed no relevant financial relationships.

Clin Cancer Res. Published online January 31, 2017. Abstract

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