Tumor-to-Tumor Metastases Involving Clear Cell Renal Cell Carcinomas: A Diagnostic Challenge for Pathologists Needing Clinical Correlation

Tumor-to-tumor metastasis is a rare event which it is specifically up to pathologists to bring to light correctly. The histological identification of such tumor-to-tumor cases is simple when the respective histologies are different but can be problematic if the case includes two carcinomas with similar cytoarchitecture viewed one inside the other under the microscope. We report four cases of this condition in which clear cell renal cell carcinoma is involved, either as a receptor or as a donor, and remark on the difficulties in recognizing some of them. Appropriate clinical-pathological correlation, including a review of the patient's antecedents and radiological exams, would be a great help in routinely identifying tumor-to-tumor metastases.

Automated summary

Tumor-to-tumor metastasis is a rare event that requires accurate identification by pathologists. It can be straightforward to identify when the tumors have different histologies, but can be challenging when two carcinomas with similar cytoarchitecture are present, one inside the other under the microscope. In this study, we report four cases involving clear cell renal cell carcinoma and highlight the difficulties in recognizing some of them. An appropriate clinical-pathological correlation, including a review of the patient's history and radiological exams, would greatly aid in routine identification of tumor-to-tumor metastases.