The Many Faces of TPM3::ALK Fusion Renal Cell Carcinoma: Case Report and Review of the Literature.

Anaplastic lymphoma kinase-rearranged renal cell carcinoma (ALK-RCC) is a rare, molecularly defined entity in the fifth edition of the World Health Organization classification of tumors. The varied presentation and histomorphology of ALK-RCC requires pathologists to have familiarity and a high degree of suspicion for this entity when faced with unusual renal tumors. Here, we present a patient diagnosed with ALK-RCC, which was clinically suspected to be urothelial carcinoma. Histomorphologic features required consideration and work-up of a broad differential diagnosis, including mesenchymal and epithelial tumors. Our report highlights features of ALK-RCC that may be more commonly found in TPM3::ALK fusion-associated tumors specifically, and also shows for the first time that ALK-RCC expresses PD-L1. Ultimately, we review the pitfalls in diagnosing this rare renal tumor with diverse presentations.