Cytokeratin immunostaining patterns of benign, reactive lymph nodes: Applications for the evaluation of sentinel lymph node specimen

The use and interpretation of cytokeratin (CK) immunostains of sentinel lym ph node specimens for breast carcinoma remain controversial. Variable immun oreactivity with anti-CK antibodies and CK-positive interstitial reticulum cells may complicate interpretation. The authors examined a series of react ive lymph nodes selected from patients without a history of malignancy. To demonstrate potential diagnostic pitfalls, three different CK antibody comb inations were studied to characterize the immunostaining patterns. Formalin -fixed sections of lymph nodes were immunostained with a labeled streptavid in-biotin method using a DAKO autostainer. The anti-CK antibody preparation s evaluated were AE1/AE3, CAM 5.2, and an inhouse-prepared CK cocktail comp osed of 7 antibodies. The authors observed that up to 10% of cells in benig n, reactive lymph nodes may be immunoreactive with anti-CK antibodies. AE1/ AE3 stained 2 of 20 cases with rare immunoreactive reticulum cells, whereas CAM 5.2 and the CK cocktail immunostained cells in 85% of cases with retic ulum cells in sinuses and the paracortex. Rare positive to 2+ cells were pr esent in a similar distribution with these two antibodies. Careful interpre tation of CK immunostaining of sentinel lymph node biopsies is essential, a s is awareness of the presence of CK-positive native reticulum. cells, to a void confusion with single cells of metastatic carcinoma.