Twenty patients with extravasation of anthracyclines were treated on a single-arm pilot study with topical 99% dimethyl sulfoxide (DMSO) and observed for 3 months with regular examinations and photographs. DMSO was applied to approximately twice the area affected by the extravasation and allowed to air dry. This was repeated every six hours for 14 days. The initial signs of extravasation included swelling in 17 patients, erythema in 15, and pain in 12. The median area of damage was 8.25 cm2 and a median of 25 minutes elapsed between extravasation and application of DMSO with one patient not treated until seven days postextravasation. Sixteen patients were observed for 3 months, two died of disease earlier after receiving 2 weeks of DMSO and three days of DMSO, respectively, and two were lost to follow-up having received one day and five days of DMSO. In no patient did extravasation progress to ulceration or require surgical intervention, suggesting with 95% confidence a true ulceration rate of between 1% and 17%. At 3 months there was no sign of residual damage in six patients, while a pigmented indurated area remained in ten. Two patients had a recall reaction with increased pain at the extravasation site when further intravenous (IV) doxorubicin was administered. The only toxicities of DMSO included a burning feeling on application subsequently associated with itch, erythema, and mild scaling. Blisters occurred in four patients. Six patients reported a characteristic breath odor associated with DMSO. Topical DMSO appears to be a safe and effective treatment for anthracycline extravasation.