A malignant cystic serous or mucinous epithelial neoplasm characterized by the presence of malignant glandular epithelial cells forming papillary structures. Stromal invasion is present. The disease is papillary cystadenocarcinoma (MONDO_0005074). Also known as: cystadenocarcinoma, papillary, malignant, papillary cystadenocarcinoma (morphologic abnormality), papillary cystadenocarcinoma, NOS (morphologic abnormality).