title: Collision metastasis of urothelial and prostate carcinomas to the same lymph node: a case report and review of the literature.
abstract: BACKGROUND
  A collision tumor is the meeting and eventual intermingling of two malignant neoplasms arising from independent topographical sites. Collision metastasis of carcinomas in the lymph nodes is a rare event. A literature search revealed only three cases of such a collision metastasis of prostatic and urothelial carcinoma, and only one of those cases had used immunohistochemical stains to distinguish the two tumors.
  
  
  METHODS
  We encountered a case of this rare entity in an 83-year-old African-American man who presented to our facility with increasing pelvic pain after a transurethral resection of a high-grade bladder tumor and a negative metastatic computed tomography chest, abdomen and pelvic scan investigation. A radical cystoprostatectomy was subsequently performed revealing a multi-centric, high-grade, ill-defined infiltrating urothelial carcinoma infiltrating the right pericystic soft tissue. A histopathological examination of the prostate revealed a multi-centric adenocarcinoma (Gleason 4 + 4) involving two pelvic lymph nodes. Interestingly, while the right pelvic lymph node was positive for metastatic prostatic adenocarcinoma alone, immunohistochemical studies of the left pelvic lymph node revealed a dual metastatic urothelial (cytokeratin-7 and pan-cytokeratin positive, prostate-specific antigen and cytokeratin-20 negative) and prostatic (prostate-specific antigen and pan-cytokeratin positive, cytokeratin-7 and cytokeratin-20 negative) carcinoma.
  
  
  CONCLUSIONS
  The collision of metastatic urothelial carcinoma and prostatic adenocarcinoma is unusual, and their biological behavior remains uncertain. A high index of suspicion along with thorough clinical examination and immunohistochemical stain results are an integral part of differentiating collision of urothelial carcinoma from prostate carcinoma, particularly when the two tumors are in close proximity with overlapping histological features.
authors.affiliation: Department of Pathology and Laboratory Medicine, Temple University Hospital, Philadelphia, PA, 19140, USA. Tapan.Bhavsar@tuhs.temple.edu.
authors.forename: Tapan
authors.initials: T
authors.lastname: Bhavsar
authors.forename: Jun
authors.initials: J
authors.lastname: Liu
authors.forename: Yajue
authors.initials: Y
authors.lastname: Huang