Oncological outcomes and HER2 expression of urothelial carcinoma with squamous differentiation: A retrospective study.

702 Background: Urothelial carcinomas (UCs) often exhibit regions of divergent differentiation, such as squamous differentiation (SqD). UCs exhibiting SqD (UCSD) are more invasive and advanced, as SqD was frequently identified in patients with advanced T stage (pT3-4) and nodal metastasis. Clinically, humanized anti-human epidermal growth factor receptor 2 (HER2) antibody conjugated with monomethyl auristatin E (DV, RC48-ADC) is a promising therapy for bladder cancer. Methods: The aim of this study was to identify the HER2 expression of UCSD and oncological outcomes. We evaluated consecutive patients underwent radical cystectomy of bladder cancer and radical nephroureterectomy of UTUC at a single institution. Her2 expression of UCSD was evaluated by immunohistochemistry in the Pathology Department of our center. Postoperative follow up was done for each patient. Results: Totally 82 patients were included, consisting of 29 UTUC and 53 bladder UC. 82.8% of upper tract UCSD had none or low HER2 expression and 71.7% bladder UCSD had none or low HER2 expression (Table 1). To this end, median follow-up time is 33 months. Many patients experience rapid recurrence and progression. Even after systematic treatment, median DFS of UCSD was 8.4 months, and median OS was 20.1 months. DV was used in 13 UCSD recurrent patients, but the ORR was relatively low (23.1%). Conclusions: Rapid progression was a significant characteristic of UCSD, and the survival outcomes of UCSD were very poor. HER2 expression of UCSD was generally low, and more effective treatment methods or clinical trials are needed for squamous differentiation subtypes. The characteristics of UCSD patients. Characteristic UCSD UTUC Bladder UC Total Number 29 53 82 Age (median) 67 69 68.5 Gender Male (%) 24 (82.8) 38 (71.7) 62 (75.6) Female 5 15 20 T-stage T1 3 7 10 T2 3 8 11 T3 19 (65.5) 27 (50.9) 46 (56.1) T4 4 (13.8) 11 (20.8) 15 (18.3) LN positive 5 (17.2) 18 (34.0) 23 (28.0) Her2 expression (%) 0 14 (48.3) 20 (37.7) 34 (41.5) 1+ 10 (34.5) 18 (34.0) 28 (34.1) 2+ 4 (13.8) 13 (24.5) 17 (20.7) 3+ 1 (3.4) 2 (3.8) 3 (3.7)