Oesophagus muscle tumour. Gross specimen of a submucosal myoma (swelling at centre) in a gullet (oesophagus) wall. A myoma is a tumour originating from muscle tissue. If it grows too large or turns cancerous (a myosarcoma), it should be surgically removed. This tumour is growing below the mucosal layer that lines the inside of the oesophagus. The oesophagus has external muscle layers (both smooth and skeletal muscle) that contract in the process of peristalsis that passes food from the mouth to the stomach.