Case Report: imaging features of anaplastic lymphoma kinase-rearranged renal cell carcinoma with a novel fusion.

Anaplastic lymphoma kinase (ALK)-rearranged renal cell carcinoma (ALK-RCC) is an extremely rare subtype of RCC, accounting for less than 1% of all cases. Its computed tomography (CT) features remain poorly characterized, hindering preoperative diagnosis. We report the case of a 34-year-old female who presented with painless gross hematuria. Abdominal ultrasound revealed a well-circumscribed, hyperechoic heterogeneous mass in the upper pole of the right kidney. Contrast-enhanced CT demonstrated a solitary, medullary-based hypodense mass with multiple punctate and patchy calcifications and mild heterogeneous enhancement. The patient underwent laparoscopic nephron-sparing surgery with complete resection. Histopathology showed papillary architecture with ISUP/WHO grade 2 atypical cells. Immunohistochemistry was diffusely positive for ALK (clone D5F3). Fluorescence in situ hybridization confirmed ALK rearrangement, and next-generation sequencing identified a novel DCTN1::ALK fusion-the first report of such a fusion in ALK-RCC. Follow-up showed no evidence of recurrence. This case highlights distinctive CT features of ALK-RCC that may raise suspicion in young patients and guide molecular testing. The identification of the fusion expands the molecular landscape of ALK-RCC and supports the potential utility of ALK inhibitors.