Considerations When Using Liquid vs Tissue Biopsy for RAS in mCRC With Single Metastatic Sites

Study findings suggest that when a plasma-based assay is being used to detect RAS mutation status in patients with metastatic colorectal cancer (mCRC) and lung or peritoneal metastasis alone, the maximum diameter and number of lesions should be carefully considered.

These data were presented at the virtual 22nd ESMO World Congress on Gastrointestinal Cancer.

“Several studies have confirmed the concordance in RAS status between liquid and tumor tissue tests, whereas possible discordance between the 2 tests has also been suggested for patients with lung metastasis alone,” wrote Yoshinori Kagawa, MD, PhD, Department of Colorectal Surgery, Kansai Rosai Hospital, Amagasaki, Japan, and colleagues, who sought to clarify whether tumor burden at baseline is associated with a discordance in RAS status in patients with single metastatic sites.

From a pool of 662 patients with mCRC involved in 3 previous studies investigating the concordance of RAS status between a plasma-based assay and tissue biopsy, Dr Kagawa et al collected data for the 224 patients who had single metastasis in the liver (n = 154), peritoneum (n = 25), or lung (n = 45).

The investigators then assessed the concordance rate based on the site of metastasis, with a focus on the link between the concordance rate and 2 tumor burden features (ie, baseline longest diameter and number of lesions).

According to the results, concordance rates were 91% (95% CI, 84.9-94.8%), 88% (95% CI, 67.7-96.8%), and 64% (95% CI, 48.7-77.7%) in patients with liver, peritoneum, and lung metastasis, respectively.

Notably, a ≥90% concordance was achieved in patients with liver metastasis regardless of the longest diameter and number of lesions; with peritoneum metastasis if they had a longest diameter ≥20 mm; and with lung metastasis alone if they had a longest diameter ≥20 mm and/or ≥10 lesions.

“Our findings suggest that the maximum diameter and number of lesions should be carefully considered when using the plasma-based BEAMing assay to detect RAS mutational status in mCRC patients with lung or peritoneal metastasis  alone,” Dr Kagawa and colleagues said.

“The underlying biology of these phenomena must be elucidated,” they concluded.—Hina M. Porcelli

Kagawa Y, Fernandez EE, Garcia-Foncillas J, et al. METABEAM study: Combined analysis of concordance studies between liquid and tissue biopsies for RAS mutations in colorectal cancer patients with single metastatic sites. Presented at: the 22nd ESMO World Congress on Gastrointestinal Cancer; July 1-4, 2020; virtual. Abstract O-21.