👉 The term "pronuclear" is a medical term used to describe a type of cancerous growth in the bone called an osteosarcoma, which is also known as a "bone tumor". This type of cancer grows from the cells that make up the bone matrix. The bones are made up of hard, compact tissue called bone matrix. Osteosarcomas can grow in any part of the body, but they are most common in the arms and legs.