Obesity

Being more than 40% above the right weight for your height. Obesity contributes to the cause of some cancers.

Occupational Therapist

Person trained to help people with any sort of disability manage day to day activities (for example, dressing, cooking etc.).

Esophagus
(Gullet)

Tube from the mouth to the stomach.

Estrogen

One of the two female sex hormones.

Estrogen Receptor
(Estrogen Receptors)

Area on the surface of a cancer cell that is triggered by estrogen. The area on the cell surface is like a lock and estrogen is the key that fits and turns the lock.

Estrogen Receptor Negative

Said of a breast cancer. Means that no Estrogen Receptors have been found on the cancer cells. This may affect the treatment given.

Estrogen Receptor Positive

Said of a breast cancer. Means that Estrogen Receptors have been found on the cancer cells. This may affect the treatment given.

Oligodendroglioma

Type of brain tumor. Glioma which develops from cells called oligodendrocytes. See Glioma.

Oncogene
(Oncogenes)

Literally means 'cancer gene'. Gene that has become abnormal and tells its cell to multiply continuously. See Chromosome, Gene, Mutation.

Oncologist

Doctor who specializes in treating cancer.

Oral
(Orally)

By mouth.

Orchidectomy

Operation to remove a testicle.

Organ Rejection

After organ transplant (for example, kidney or heart transplant) many people take drugs to stop them rejecting their new organ. These drugs suppress their immune systems and this can make them more at risk for some other diseases, for example, Non Hodgkin's Lymphoma. See Immune System, Non Hodgkin's Lymphoma.

Orgasm

Sexual climax.

Osteoporosis

Losing calcium from the bones, making them weaker. Often gives a lacy appearance to the bone with holes appearing. Sometimes called bone thinning.

Osteosarcoma

Type of primary bone cancer.

Ovarian Ablation

Using Chemotherapy or Radiotherapy to stop a woman's ovaries from working. This stops the production of sex hormones and is useful in treating cancers which use sex hormones to grow (for example, breast cancer). Will result in an early menopause.

Ovarian Removal

Also called oophorectomy. Surgery to take out the ovaries. This stops the production of sex hormones and is useful in treating cancers which use sex hormones to grow (for example, breast cancer). Will result in an early menopause.

Ovary
(Ovaries)

Glands either side of the womb in women. Produce eggs and the female sex hormones. See Hormones, Sex Hormones.

Overview
(Overviews)

Similar to meta-analyses. Putting together the results of more than one trial. See Clinical Trials, Meta-analysis.

Oxygen

Gas that makes up one fifth of the air we breathe. Oxygen is essential for life.