RB1 and cancer: <b>Case presentation:</b> In an exploratory case of a 57-year-old man diagnosed with metastatic sigmoid adenocarcinoma, we used a hotspot panel of cancer-associated gene mutations to identify tumor-specific mutations in the primary tumor and metastasis.<h4>Results</h4>Five mutations were detected (<i>KRAS</i>, p.Gly12Val; <i>TP53</i>, p.Arg175His; <i>RB1</i>, p.Ile680Thr; <i>ALK</i>, p.Gly1184Glu; and <i>ERBB2</i>, p.Lys860Lys), of which three were detected in both tissue types (primary tumor and metastasis).