High-grade Serous Neoplasm of Fallopian Tube Mimicking a Low-grade Lesion.

Low-grade and high-grade serous neoplasms are generally considered to be separate entities with distinct morphologic features, pathogenesis and clinical behavior. However, rare tumors defy this dualistic classification. Herein, we describe an incidental serous neoplasm confined to the fallopian tube with both low-grade and high-grade features, including ciliated cells and low proliferative rate, along with variable nuclear pleomorphism and an aberrant p53 cytoplasmic expression pattern by immunohistochemistry. Whole exome sequencing revealed a subclonal TP53 splice mutation, supporting this to be an unusual high-grade serous neoplasm of the fallopian tube, which likely evolved from a low-grade serous precursor. This case highlights issues concerning the definition and diagnostic criteria for serous tubal intraepithelial carcinoma and further demonstrates high-grade transformation of low-grade serous neoplasia to be an early pathogenic event.