DISCLAIMER: this is not medical advice; do your own research, and take responsibility for your own actions.
Petty spurge, or radium weed, is Euphorbia peplus, a common winter-time weed in the southwest of Western Australia. I have put its white sap, which burns and must not be used orally or go near the eyes or nasal inner surfaces, on low-level skin cancers, not melanomas, such as little sores which never heal. It is advised that only one application is needed. I typically apply it for 3 days in a row, but the resulting burn is significant and usually hurts; I apply aloe vera gel a few hours after each application, and then for the next several days after white sap application. I will experiment with aged urine for the next couple of weeks, to try to accelerate the area’s healing.