- Oncogene – Oncogenes play a role in cell growth and are normally found in cells. When an oncogene is damaged, it causes cells to grow too quickly and form tumors.
- Oncologist – A doctor who specializes in the treatment of cancer.
- Oncology – The branch of medicine that focuses on the study and treatment of cancer.
- Osteoporosis – A disease that causes bones to become weak and fragile.