Ovarian tumour. Light micrograph of a section through a malignant (cancerous) serous cystic tumour in an ovary. This form of tumour is known as a serous papillary cystadenocarcinoma. These tumours develop as large masses, virtually replacing the ovary. In this malignant variety the papillary ingrowths (frond-like) can be seen filling the cystic cavity.