An invasive adenocarcinoma characterized by cystic changes and the presence of malignant glandular cells which contain intracytoplasmic mucin. It may arise from the ovary, pancreas, appendix, and lung. The disease is mucinous cystadenocarcinoma (MONDO_0005858). Also known as: Pseudomucinous adenocarcinoma, Pseudomucinous cystadenocarcinoma, mucinous cystadenocarcinoma (morphologic abnormality), mucinous cystadenocarcinoma NOS (morphologic abnormality).