PTEN is a tumour protection gene that helps to protect against benign (non-cancerous) and malignant (cancerous) tumours.
Everyone has two PTEN genes (one from their mother, and one from their father). If one of the genes is not working, this is known as having a faulty PTEN gene, or having a PTEN mutation. People with a faulty PTEN gene are known to have Cowden syndrome. Cowden syndrome is part of the PTEN Hamartoma syndrome.