As proud flesh is a type of fibrous tumor, there has been speculation that it may be cancerous but it has not been scientifically linked to any form of cancer.
In order for proud flesh to become cancerous, it would have to form from a cancer cell and replace normal tissue with the cancerous cells. It has not been found to form in this way. Proud flesh is most often caused by a wound or injury, so if it eventually develops into a tumor, it is more likely to be benign than malignant (cancerous).