Light micrograph section through human tissue showing an endocrine tumour. Most endocrine tumours are non-cancerous (benign), but some are cancerous (malignant). Endocrine tumours occur in hormone-producing glands of the endocrine system that includes the thyroid, parathyroid, adrenal glands, pancreas, intestines and pituitary glands. Tumours arising in these glands can produce hormones themselves, which can lead to serious illness. The most common sort of endocrine cancer is thyroid cancer which begins in the thyroid gland.