Thyroid cancer. Coloured scintigram of a malignant (cancerous) tumour (dark blue) in a thyroid gland. The thyroid is an endocrine gland found in the neck, responsible for the production of hormones controlling the body's metabolism. The cause of thyroid cancer is not known. It is more common in women than men. Symptoms can include swelling in the neck and difficulty swallowing or breathing. Treatment is with the surgical removal of the tumour or gland, often combined with radioactive iodine therapy. A scintigram shows the activity of the thyroid gland using a radioactive iodine tracer, which emits gamma rays that are detected by a gamma camera.