Malignant transformation is the change of cells from benign to malignant behavior. Usually this diagnosis is made by pathologic examination of tissues. However, often the physician during the history and physical examination can find that there have been changes in size or patient sensation and upon direct examination that there has been a change in the lesion itself.

Malignant transformation is a synonym for progression to malignancy. Transformation may take place as a primary or a secondary process.

Although malignant transformation may occur because of changes within the cell, it can be induced by inorganic substances and toxins such as cadmium or arsenite and organic substances such as tobacco-specific nitrosamines. It is also thought that some malignant transformation is due to viruses such as the Epstein-Barr virus.

Risk assessments can be done and are known for certain populations. One of the better known of these progression and risks is the progression of a nevus to melanoma.

This differs from benign growths with malignant intent .