Clinicopathological features of lipid cell variant of urothelial carcinoma.

487 Background: Lipid cell variant (LCV) of urothelial carcinoma (UC) which was first described by Mostofi et al in 1999 is a very rare variant of UC. Because it has only been documented in occasional case reports and a small series about this variant since then, clinicopathological characteristics of LCV are not yet clarified. In this study, we assessed the clinicopathological characteristics of LCV experienced in our hospital. Methods: The medical records of patients with LCV, who were treated in our hospital between September 2015 and September 2017, were retrospectively reviewed and analyzed. Results: In this period, of 301 patients undergoing TURBT and 42 patients undergoing nephroureterectomy, 13 patients including 10 patients with bladder cancer and 3 with pelvic ureter cancer, were found to be diagnosed as LCV of UC at our hospital. The median observation period of these patients was 6 months (IQR, 4-9 months). Among 10 bladder cancer patients who had confirmed this variant in transurethral resection of bladder tumor (TURBT) specimens, all cases had concurrent high-grade UC and the most cases had tumor features including pT2 or more local stages and lympho-vascular invasion (LVI) positive. Co-existence of micropapillary and/or plasmacytoid variant were seen in 5 patients. Lymph node metastases were observed in 3 patients, and this variant was histologically confirmed within the lymph node metastatic tissue in one case. No patient had distant metastasis. Among 3 pelvic ureter cancer patients who had undergone nephroureterectomy, all cases had concurrent high-grade UC and the most cases had tumor features including pT3 local stage and LVI positive. Micropapillary variant was coexisted in one patient. No patient had distant metastasis. 7 patients were no evidence of disease and 6 were alive with disease. The estimated median time from surgery to recurrence was not reached. The 6-months disease-free survival rate was 59%. Conclusions: LCV is seen in the patients who have high-grade UC, and tends to be accompanied with other aggressive variants including micropapillary and plasmacytoid. All patients with this variant had advanced stage cancer at presentation with high recurrence rates.