It is well established that lymph nodes (and other lymphoid tissues) contain cytokeratin positive cells that are NOT metastatic carcinoma cells. They are called "extrafollicular dendritic cells".  Dr. Allen Gown, Director and Chief Pathologist at PhenoPath Laboratories in Seattle, recently gave me two references that discuss these cells: 

Gould VE, et al: Increased numbers of cytokeratin-positive interstitial reticulum cells (CIRC) in reactive, inflammatory and neoplastic lymphadenopathies: hyperplasia or induced expression?  Virchows Arch 425:617-629 (1995), and

Franke WW and Moll R: Cytoskeletal components of lymphoid organs.  I.  Synthesis of cytokeratins 8 and 18 and desmin in subpopulations of extrafollicular reticulum cells of human lymph nodes, tonsils, and spleen.  Differentiation 36:145-163 (1987).

If you are using the right cytokeratin mAbs and a sensitive detection system (with sufficient antigen retrieval) you should see these cells in most lymph nodes.  We use a cytokeratin cocktail consisting of AE1&AE3 and CAM5.2 (along with pepsin digestion) for screening lymph nodes for metastatic disease.  If you don't see these immunoreactive cells there may be something wrong with your technique.

R. Cartun