ABSTRACT
Objective: To investigate the clinicopathological features, molecular characteristics, differential diagnosis and prognosis of anaplastic lymphoma kinase (ALK)-translocation renal cell carcinoma. Methods: Two cases of ALK-translocation renal cell carcinoma diagnosed from January 2011 to December 2020 were retrospectively analyzed to characterize their morphological features, immunohistochemical expression and prognosis. Multiple molecular studies including fluorescence in situ hybridization (FISH), reverse transcriptase-polymerase chain reaction (RT-PCR), and next-generation sequencing were performed to characterize the genetic alterations. Results: Two patients included one male and one female, with 59 and 57 years old, respectively. Morphologically, case 1 resembled collecting duct carcinoma or renal medullary carcinoma, which demonstrated tubular, microcapsule and reticular structures, with a remarkable myxoid background and lymphocytes infiltration; case 2 resembled Xp11.2 translocation renal cell carcinoma or type 2 papillary renal cell carcinoma, which demonstrated tubular papillary and focal solid structures, with flocculent cytoplasm and many foamy histiocytes, but without myxoid background and lymphocytes infiltration. Immunohistochemistry showed strongly positive expression of ALK. CK7, E-cadherin, vimentin, PAX8 and CD10 showed various degrees of expression, and other antibodies were nonreactive. A variety of molecular assays showed definite ALK gene translocation, with rare VCL-ALK gene fusion (VCL exon and 16-ALK exon 20) in case 1, and EML4-ALK gene fusion (EML4 exon and 2-ALK exon 20) in case 2. Conclusions: ALK-translocation renal cell carcinoma is rare with various morphological features, and is easy to miss and misdiagnose. The characteristic ALK expression and molecular detection of ALK translocation are helpful for diagnosing this type of renal cell carcinoma.