Prostatic and urothelial metastasis in the same lymph node: a case report.

BACKGROUND: Collision metastasis is a rare phenomenon in which metastases of carcinoma from 2 separate primary tumors occur in the same lymph node. We summarize here the clinical course and highlight the histological challenges in the diagnosis of this rare phenomenon. CASE: A biopsy performed due to gross hematuria by endoscopic resection revealed an infiltrative high-grade urothelial carcinoma in a 75-year-old man receiving androgen deprivation therapy due to biopsy-proven high-grade prostate cancer. A radical cystectomy, with regional lymphadenectomy and prostatectomy, was performed. Three nodes appeared to have metastatic foci from both primary tumors: prostatic and urothelial cancer. The presence of the 2 tumor types colliding in the same lymph nodes was confirmed by immunohistochemical stains.
CONCLUSION: In a patient with simultaneous tumors it is important to remember that a part of lymph node metastases with histological polymorphic appearance may result from a collision metastasis. In light of the important therapeutic consequences, a differential diagnosis is needed, suggesting appropriate immunohistochemical investigations.