This is the first in a four-part continuing education series on cytolo
gy. This article discusses the role of immunocytochemistry in the labo
ratory. The technique and its applications are discussed, with markers
of tumor classification and markers of tumor behavior highlighted. Th
e second article of the series is on cancer cytogenetics. Following ar
ticles will be about fine-needle aspiration and cytology's relationshi
p to laboratory service. This article focuses on cytology's increasing
ly important role in disease diagnosis. Because cytologic samples may
be the only diagnostic samples available from patients with cancer, ma
ny tests traditionally performed on histologic material are now being
performed on cytologic samples. Immunocytochemistry is one technique s
hown to be important in diagnostic tumor pathology.