Endocrine tumour. Light micrograph of a section through an apudoma, showing the characteristic small, uniform cells and granular cytoplasm. Apudomas are tumours that arise from APUD (amine precursor uptake decarboxylase) cells. They can be benign or malignant and mainly occur in the gastrointestinal tract, pancreas and thyroid glands. APUD cells are a diverse group of apparently unrelated endocrine cells that synthesise and secrete peptide and amine hormones.