Abstract
546 Background: The antibody-drug conjugate enfortumab vedotin is poised to change the bladder cancer (BC) treatment landscape by targeting Nectin-4, near ubiquitously expressed in urothelial cancer (UC). Less is known about this and other targets in BC with pure or mixed variant histology (VH). Methods: Immunohistochemistry (IHC) was performed on a Ventana Discovery Autostainer (Roche Diagnostics) using an ultraView DAB detection kit (Roche Diagnostics) and a Nectin-4 polyclonal antibody (1:100 dilution; Abcam, Cambridge, UK). The intensity and extent of Nectin-4 expression was determined by the histochemical scoring (H-score) used in preclinical testing, defined as the sum of the products of the staining intensity (score of 0–3) x % of cells (0–100) stained at a given intensity. Specimens were assessed by H score as: negative (0–14), weak (15–99), moderate (100–199), and strong (200–300). Results: Forty UC and VH BC were evaluated for Nectin-4 expression by IHC: 15 small cell (SCBC) (8 pure SCBC, 6 mixed SCBC/UC, 1 SCBC/CIS), 8 carcinosarcomas (CS) (7 pure CS, 1 HGUC/sarcomatoid features), and 17 pure HGUCs. Normal urothelium and stroma were negative. Eight of 8 (100%) pure SCBC were negative for Nectin-4. Six of 7 (85.3%) mixed SCBC+HGUC/CIS had weak staining and 1/7 (14.7%) had moderate staining in the urothelial components (comp) while 7/7 (100%) of the SCBC comp were negative. Seven of 7 (100%) pure CS were negative and 1/1 (100%) mixed CS+HGUC showed weak staining in the HGUC comp while the sarcomatoid comp was negative. Expression in UC was: 1/17 (5.9%) strong, 3/17 (17.6%) moderate, 10/17 (58.8%) weak, and 3/17 (17.6%) negative. Gene expression profiling confirmed Nectin-4 was downregulated in VH compared to UC samples, as was ERBB2 and Trop2. Conclusions: There is heterogeneity of expression of Nectin-4 and other targets in BC with VH compared to UC. This may have therapeutic implications, and highlights need for additional research in VH.[Table: see text]
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