Utility of a comprehensive immunohistochemical panel in the differential diagnosis of spindle cell lesions of the urinary bladder.

Spindle cell lesions of the urinary bladder are uncommon, but when encountered in clinical practice, pose a difficult diagnostic challenge as the differential diagnostic considerations are vast. Pseudosarcomatous processes significantly overlap with malignant tumors (sarcomatoid urothelial carcinoma and leiomyosarcoma) in their morphology and published immunohistochemical profile [pancytokeratin pan (CK), smooth muscle actin (SMA), and desmin]. p63 has been studied rarely and CK 5/6 and CK 34betaE12 have not been analyzed in the bladder in this diagnostic context. In the current study, 45 typical examples of spindle cell lesions [10 pseudosarcomatous myofibroblastic proliferations (PMP), 22 sarcomatoid urothelial carcinomas, and 13 smooth muscle tumors] of the urinary bladder were immunostained with a panel containing broad spectrum anticytokeratin antibodies (OSCAR or AE1/AE3), as well as antibodies to CK 34betaE12, CK 5/6, p63, SMA, and anaplastic lymphoma kinase (ALK). The immunoreactivity was as follows: PMP-CK (OSCAR) 7/10 (70%), CK (AE1/AE3) 7/9 (78%), CK 34betaE12 0/10 (0%), CK 5/6 0/9 (0%), p63 0/9 (0%), SMA 10/10 (100%), ALK 2/10 (20%); sarcomatoid urothelial carcinoma-CK (OSCAR) 15/22 (68%), CK (AE1/AE3) 14/20 (70%), CK 34betaE12 5/20 (25%), CK5/6 6/22 (27%), p63 11/22 (50%), SMA 16/22 (73%), ALK 0/22 (0%); and smooth muscle tumors-CK (OSCAR) 7/13 (54%), CK (AE1/AE3) 7/12 (58%), CK 34betaE12 0/12 (0%), CK 5/6 0/12 (0%), p63 3/13 (23%), SMA 11/13 (85%), ALK 0/13 (0%). Positivity for keratin was typically focal to moderate in smooth muscle tumors and more commonly moderate to diffuse in sarcomatoid carcinomas and PMP. Our data indicate that there is significant immunohistochemical overlap between the different spindle cell lesions, each of which has unique clinicopathologic, prognostic, and therapeutic ramifications. Within the context of morphology, an immunohistochemical panel composed of broad-spectrum antibodies to cytokeratin as well as antibodies to SMA, ALK, p63, and CK 5/6 will be a useful diagnostic adjunct: a combination of pankeratin, SMA, and ALK positivity favors PMP; expression of several cytokeratin and especially CK 34betaE12 and CK 5/6 with p63 favors sarcomatoid carcinoma and SMA positivity with overall absence of other markers favors leiomyosarcoma.