Background: Sarcopenia or degenerative loss of skeletal muscle mass is related to poor prognosis in patients with cancer. This study aimed to clarify the clinical significance of skeletal muscle loss (SML) during chemotherapy for metastatic colorectal cancer (mCRC). Methods: A total of 249 patients who were secondarily registered in a pooled database of mCRC patients with the first-line systemic chemotherapy and prospectively enrolled in six clinical trials of Kyushu Study Group of Clinical Cancer were included in this study. Skeletal muscle area was calculated from computed tomography images before and 3 and 6 months after treatment. Baseline sarcopenia and SML (cut-off value = 9%) were evaluated. Results: Baseline sarcopenia was observed in 135 of 219 patients who were evaluated before treatment. They tended to be male; older; and have lower body mass index, lower visceral and subcutaneous fat contents, and a lower waist circumference (P < 0.01); however, baseline sarcopenia was not associated with prognosis. SML at 3 months was associated with an incidence of adverse events (P = 0.01), poor objective response rate (ORR) (P < 0.01), and poor progression-free survival (PFS) (P = 0.03), and it was an independent predictive factor for poor ORR (P < 0.01) and PFS (P = 0.04). Conclusion: SML at 3 months after systemic chemotherapy for mCRC was associated with poor treatment response. Thus, clarifying the importance of SML prevention guarantees a more effective chemotherapy.
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