TFE3-positive renal cell carcinomas are not always Xp11 translocation carcinomas: Report of a case with a TPM3-ALK translocation.

Translocation-associated renal cell carcinoma (RCC) is a distinct subtype of RCC with gene rearrangements of the TFE3 or TFEB loci. The TFE3 gene is located at Xp11 and can fuse to a number of translocation partners, resulting in high nuclear expression of TFE3 protein. TFE3 immunostaining is often used as a surrogate marker for a TFE3 translocation. We report a case of an RCC that expressed TFE3 but showed only gain of TFE3 rather than a translocation. Moreover, this case had a t(1;2) translocation fusing ALK and TMP3, identical to that seen in inflammatory myofibroblastic tumour. There was resulting overexpression of ALK protein in a cytoplasmic and membranous pattern. The patient was not treated with chemotherapy but following regional nodal recurrence, an ALK inhibitor was added and the patient remains alive one year later. There are only rare reports of RCC with an ALK-TMP3 fusion, and these tumours can express TFE3 on some unknown basis not related to a TFE3 translocation. Any RCC positive for TFE3 and lacking a translocation should be tested for ALK expression and translocation. Recognition of this subtype of RCC will allow ALK inhibitor therapy to be added, in the hope of improving patient outcome.