Women with low muscle mass have worse prognosis in breast cancer treatment, reveals research

Maintaining muscle mass has proven to be crucial for patients undergoing cancer treatment. Studies have shown that individuals with more muscle tend to respond better to therapies such as chemotherapy and radiotherapy. They also have a lower risk of complications and experience more effective recovery. This is because muscle plays an essential role in metabolism, helping to regulate the inflammatory response and drug absorption. Conversely, cancer patients with low muscle mass have a higher risk of experiencing toxicity during treatment, which can result in a worse prognosis and lower survival rate.

A study carried out at the Ribeirão Preto School of Medicine of the University of São Paulo (FMRP-USP), in Brazil, supported by FAPESP, evaluated data from women who had recently been diagnosed with breast cancer. The study confirmed that those with lower muscle mass at the start of the follow-up period had a worse prognosis than those with normal muscle mass. The results were published in the journal Discover Oncology.

The study is part of a secondary analysis of a larger study that examined chemotherapy-related metabolic changes in women with breast cancer. The researchers aimed to evaluate the possible associations between markers of muscle mass assessed by computed tomography and phase angle results obtained from bioimpedance analysis.

A total of 54 patients were recruited from the Mastology Outpatient Clinic at the “Hospital das Clínicas,” a general and teaching hospital affiliated with FMRP-USP and a regional reference in Brazil. All of the patients had been diagnosed with early-stage breast cancer and were referred for chemotherapy. However, before beginning treatment, they all underwent anthropometric assessments, bioimpedance testing, and CT scans with analysis of the third lumbar vertebra. They also underwent physical function tests, such as handgrip strength and gait speed tests, as well as blood tests.

According to Mirele Savegnago Mialich Grecco, a nutritionist, author of the article, and researcher at the Department of Health Sciences at FMRP-USP, women with breast cancer are predisposed to loss of mass, impaired muscle quality, and decreased strength during treatment. These changes can predict adverse outcomes, including mortality.

This audience was chosen for the study because there are many patients who are overweight or obese, which can end up masking the true state of the patient’s body composition. “Often, this excess weight gives the false impression that everything is fine with that woman, as if she had a greater reserve of muscle mass. The treatment is highly toxic and generates a very important inflammatory response, which favors the reduction of this muscle mass over the course of the journey,” she explains.

Grecco also stresses that, in most cases, breast cancer patients do not fit the stereotype of cancer patients with tumors in other regions, who tend to lose weight more quickly and evidently. This can hinder the detection of muscle mass loss. “If we don’t evaluate that woman more thoroughly, the decrease in mass can go unnoticed,” she says.

How the results were obtained

Chest CT scans are part of the routine treatment for these patients. The researchers took a sample of images from the lumbar region (specifically the L3 vertebra) to analyze muscle mass quantity and quality in women with cancer before they started chemotherapy or other treatments.

However, since CT scans are not always available or practical for assessing body composition in clinical practice, the researchers also analyzed phase angle (PhA) as an alternative method. This is a measure associated with membrane integrity that is obtained by bioimpedance analysis. It is a quick, non-invasive tool that can reflect body composition.

“It’s a portable, low-cost, and widely accessible method for assessing individuals in clinical settings. However, specific knowledge is required to correctly interpret the results,” ponders Grecco.

Five years later, the researchers reviewed these patients’ medical records to check mortality during the period. The results showed that women with non-metastatic breast cancer and low muscle mass had a significantly lower survival rate than those with normal muscle mass.

In addition, individuals with low muscle mass also had lower phase angles, which was associated with a worse prognosis and negatively affected patient survival, regardless of age or cancer stage. According to Grecco, this means that phase angle measurement has emerged as a promising marker of general health and could be a valuable clinical tool for assessing prognosis.

Impact on real life

Breast cancer is one of the leading causes of cancer death among women. In Brazil, the National Cancer Institute (INCA) estimates nearly 74,000 new cases of the disease per year and 18,000 deaths between 2023 and 2025. According to the Ministry of Health, the public network registered 60,866 cases of this cancer in women in 2023 alone – 11% of whom were under 40 years of age.

According to the study, the prevalence of low muscle mass among cancer patients varies widely, from 38% to 70%. For breast cancer specifically, studies report a prevalence close to 40%. In this population, reduced muscle mass has been associated with treatment failure, chemotherapy toxicity, decreased physical activity, tumor progression, and shorter survival.

According to Grecco, loss of muscle mass during cancer treatment is expected but not desired. For this reason, accurately assessing body composition is essential for monitoring metabolic changes related to the disease and guiding targeted nutritional interventions, especially in populations where greater adiposity can mask these changes. Thus, the aim of the study was to try to identify more practical measures that can be incorporated into clinical routines to enable health professionals to intervene earlier for these patients.

“Our idea with this work is to take a more in-depth look and propose an earlier protein intake for that woman, as soon as she’s diagnosed with breast cancer, indicating the amount of protein she’d need to eat per day, for example,” says the nutritionist.

Another suggestion is that health professionals should monitor patients’ muscle mass from the outset and refer them to a physical exercise program as their condition allows. “Especially resistance and strength exercises, which will help preserve muscle mass a little more. The idea isn’t to promote muscle gain, but rather to minimize loss and better enable that woman’s body to withstand all the cancer treatment,” the researcher stresses.

Reference:

Mialich, M.S., da Silva, B.R., Amstalden, B.T. et al. Association of skeletal muscle quantity and quality with mortality in women with nonmetastatic breast cancer. Discov Onc 16, 247 (2025). https://doi.org/10.1007/s12672-025-01999-1.