A malignant epithelial tumour arising from the glandular structures, which are constituent parts of most organs of the body. The term is also applied to tumours showing a glandular growth pattern. These tumours may be subclassified according to the substances that they produce, for example mucus-secreting and serous adenocarcinomas, or to the microscopical arrangement of their cells into patterns, for example papillary and follicular adenocarcinomas. They may be solid or cystic (cystadenocarcinomas). Each organ may produce tumours showing a variety of histological types; for example, the ovary may produce both mucinous and serous cystadenocarcinomas.