Oesophageal smooth muscle tumours do not usually transform into oesophageal cancer. Esophageal smooth muscle tumour is a benign tumour formed by the overgrowth of muscle cells in the wall of the esophagus, which grows slowly, does not invade the surrounding organs and has no metastasis.
In contrast, malignant tumours of the oesophagus grow rapidly and can invade surrounding organs and metastasise to other parts of the body via lymphatic vessels and blood vessels. There is no clear evidence in large samples that both can transform from benign to malignant.