[ALK-rearranged renal cell carcinoma: a clinicopathological analysis of three cases].

Objective: To explore the clinicopathological and molecular genetic characteristics of anaplastic lymphoma kinase (ALK)-rearranged renal cell carcinoma (RCC), including a rare case with the TPM1-ALK gene subtype. Methods: Three cases of ALK-rearranged RCC diagnosed in the Department of Pathology, the First Affiliated Hospital of Zhengzhou University, Zhengzhou, China from January 2020 to December 2024 were collected. Their clinical pathological and next-generation sequencing (NGS) data were analyzed. Relevant literature was also reviewed, and follow-ups were carried out. Results: Among the three patients, there were 1 female (case 1) and 2 males (cases 2 and 3), with the ages of 29,41 and 44 years, respectively. All of them were presented with space-occupying renal lesions. Case 1 (KIAA1217-ALK RCC) showed mixed cystic and solid components under the microscope, with tubular, papillary, and cribriform arrangements. The tumor cells had clear boundaries, and were cubic or low columnar, arranged in a single layer, pseudostratified or in sheets. The cytoplasm was abundant and eosinophilic, and part of the cytoplasm was vacuolated, as if there was accumulation of mucoid substances. The tumor cell nuclei were oval with prominent nucleoli. A large amount of mucus and inflammatory cell infiltration were noted in the stroma. Case 2 (TPM1-ALK RCC) showed a papillary growth pattern, with small, slender papillae accompanied by branches. The cells were arranged in a single layer, and the cytoplasm was either eosinophilic or clear. Foamy cells were aggregated in the stroma, accompanied by psammoma body-like calcifications. Case 3 (EML4-ALK RCC) was characterized by papillary and tubulocystic structures. The cytoplasm was abundant and eosinophilic. The tumor cell nuclei were large, with prominent nucleoli. There was conspicuous infiltration of lymphocytes and neutrophils in the fibromuscular stroma. The tumor cells all expressed epithelial markers, PAX8, GATA3, P504s and FH. ALK (5A4) staining showed diffuse strong expression in the cytoplasm, while TFE-3 was positive (nuclear stain) only in case 1 and case 3. The fluorescence in situ hybridization showed that ALK gene rearrangement was present in all three cases, while TFE-3 gene rearrangement/mutation was not detectable in case 1 and case 3. NGS showed the KIAA1217::ALK fusion (the fusion site in the exon 11 of KIAA1217 and exon 18 of ALK) in case 1, the TPM1::ALK fusion (the exon 8 of TPM1 and exon 20 of ALK) in case 2, and the EML4::ALK fusion (the exon 2 region of EML4 and the exon 20 region of ALK) in case 3. Conclusions: ALK-rearranged RCC has unique molecular characteristics. Its histological morphology is easily confused with that of papillary RCC and TFE3-rearranged RCC. Both immunohistochemistry and gene rearrangement tests should be used to confirm the diagnosis.