Sarag Aboujafar Boukhar, Ricky Kaneshiro, Alan Schiller, Keith Terada, Pamela Tauchi-Nishi

Endometrial cancer is the most common gynecologic malignancy in the United States. However, bony metastasis is infrequent and exceptionally rare as the initial presentation. We report a case of a 77-year-old female with a clinically silent endometrial carcinoma who presented with a left tibial metastasis as the first manifestation of her disease. Ours is only the third case diagnosed by fine-needle aspiration (FNA) cytology, and the first to detail the cytomorphologic features of metastatic endometrial cancer to bone. These microscopic findings, including three-dimensional cohesive clusters with cellular overlapping and cuboidal to columnar cells exhibiting low nuclear: cytoplasmic ratios and partially vacuolated cytoplasm, differ significantly from those of endometrial carcinoma on a Papanicolaou test. The tumor bore similarity to the more commonly encountered metastatic colon cancer, but immunohistochemical staining enabled reliable distinction between these entities. A review of osseous metastases of endometrial cancer demonstrates a predilection for bones of the lower extremity and pelvis with a predominance of the endometrioid histologic subtype. In about a quarter of the cases, the bony metastasis was the first manifestation of the cancer. FNA was an effective diagnostic modality for this unusual presentation of a common malignancy. Awareness of this entity and its differential diagnosis is essential for accurate and timely diagnosis.