This report presents some of the changes in the subcutaneous tissue at the site of catheter insertion of a patient undergoing chemotherapy. The site was observed by ultrasonography at 5 time points, namely, before insertion, immediately after treatment, after 1, 3, and 4 weeks. Some practice guidelines do not recommend the use of a peripheral intravenous catheter for irritant or vesicant continuous administration to avoid vessel damage. 1,2 However, peripheral intravenous catheters are unavoidably used in some patients for drug administration because of their conditions, such as superior vena cava syndrome, coagulopathy, or compromised condition. In clinical settings, induration can be observed at the catheterization sites after anticancer drug administration even without obvious signs and symptoms of extravasation such as feelings of tingling, burning, pain, swelling, and redness at the