title: Macrophage-rich reaction in lymph nodes as a mimic of metastatic renal cell carcinoma on fine needle aspiration. A case report.
abstract: BACKGROUND
  Renal cell carcinomas have a high metastatic potential. Many of them are occult at initial presentation and mimic a primary neoplasm of the metastatic site. However, not all lymph node enlargements in a patient with a history of renal cell carcinoma are due to metastasis. Foamy macrophages can mimic metastatic renal cell carcinoma cells.
  
  
  METHODS
  A 60-year-old male with a known diagnosis of renal cell carcinoma of clear cell type developed enlarged neck nodes 44 months after the diagnosis. These were aspirated to yield cystic fluid that, on smears, showed numerous clear cells with low nuclear grade. Immunohistochemical stains revealed these cells to be foamy macrophages (CD68 immunoreactive) and not metastatic renal cell carcinoma, as had been suspected on initial examination of Diff-Quik and Papanicolaou-stained smears.
  
  
  CONCLUSIONS
  Immunohistochemistry is a valuable adjunct in avoiding a false diagnosis of metastatic carcinoma in macrophage-rich nodal reactions in patients with a history of renal cell carcinoma.
authors.affiliation: Department of Pathology, B216, University of Colorado Health Sciences Center, 4200 East 9th Avenue, Denver, Colorado 80262, USA.
authors.forename: M
authors.initials: M
authors.lastname: Singh
authors.forename: E
authors.initials: E
authors.lastname: Wu
authors.forename: K R
authors.initials: KR
authors.lastname: Shroyer
mesh_terms: D015703:Antigens, CD / Q000032:analysis / Q000276:immunology; D015214:Antigens, Differentiation, Myelomonocytic / Q000032:analysis / Q000276:immunology; D001707:Biopsy, Needle; D002292:Carcinoma, Renal Cell / Q000473:pathology* / Q000556:secondary; D003937:Diagnosis, Differential; D005487:Foam Cells / Q000737:chemistry / Q000473:pathology; D006801:Humans; D007150:Immunohistochemistry; D007680:Kidney Neoplasms / Q000473:pathology*; D008198:Lymph Nodes / Q000473:pathology; D008199:Lymphadenitis / Q000473:pathology*; D008207:Lymphatic Metastasis; D008297:Male; D008875:Middle Aged; D000097382:CD68 Molecule
chemical_list: D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; C067980:CD68 antigen, human; D000097382:CD68 Molecule