Renal Cell Carcinoma, Unclassified with Medullary Phenotype and Synchronous Renal Clear Cell Carcinoma Present in a Patient with No Sickle Cell Trait/Disease: Diagnostic and Therapeutic Challenges.

Renal medullary carcinoma (RMC) is an aggressive high-grade renal cell carcinoma (RCC) associated almost exclusively with sickle cell trait or sickle cell disease. However, RCC with RMC features has rarely been reported in patients with no sickle cell trait or disease. Renal cell carcinoma unclassified with medullary phenotype (RCCU-MP) is a newly-coined term used by an international panel of experts to describe renal cell carcinoma showing morphologic and immunohistochemical features of renal medullary carcinoma in patients without sickle cell trait/disease. So far, only one study in the English literature has described five such cases. Here, we report a case with unique clinical and pathological features in a 76-year-old male patient without sickle cell trait. The patient had a history of colon cancer with liver and lung metastases and was found to have a new renal mass in his right kidney during the follow up. A right nephrectomy was performed and showed two separate masses (tumor 1 and tumor 2). Tumor 1 had histologic features of RMC and the tumor cells were positive for CK7, Pax8, and OCT4 and showed loss of nuclear INI1 expression. Tumor 1 was diagnosed as RCCU-MP (6.3 cm, pT3aNx, WHO/ISUP nuclear grade 3). Tumor 2 showed features of clear cell type of RCC (0.6 cm, pT1aNx, WHO/ISUP grade 2) with intact nuclear INI1 expression. Three-months post-nephrectomy, the patient developed lung metastasis of RCCU-MP. To the best of our knowledge, this was the first documented case with synchronous RCCU-MP and clear cell RCC presenting in a patient without sickle cell trait. Careful histologic assessment with a panel of immunohistochemical biomarkers was helpful to render a correct diagnosis for early aggressive treatment. Copyright