IMMUNOCYTOCHEMICAL STAINING OF CYTOLOGIC SPECIMENS - HOW HELPFUL IS IT

The contribution of immunocytochemical (ICC) staining to the diagnosis of a range of cytologic specimens reported over a 20-month period was retrospectively assessed. A total of 194 cases (1.6% of total workloa d) were stained for diagnostic purposes in this period. Immunocytochem ical staining was determined to be helpful in 75.8% of cases. In body fluid cases (105), staining was most often performed to assist with th e discrimination of mesothelial cells and metastatic malignancy. Immun ocytochemical staining was helpful in 82% of fluid specimens, with the preliminary diagnosis confirmed in 64%, refined in 8%, and revised in 10% of cases. In fine-needle aspiration (FNA) specimens, staining was helpful in 69%, resulting in a refinement of diagnosis in 55%, and co nfirming the preliminary diagnosis in 14%. The preliminary diagnosis w as revised in a single FNA case. Immunocytochemical staining was parti cularly valuable in assisting the subclassification of poorly differen tiated malignancies. A more precise diagnosis was possible following c onsideration of ICC results in 68% of cases with a preliminary diagnos is of poorly differentiated malignancy. Immunocytochemical staining wa s also helpful in identifying the primary site of metastatic carcinoma in six FNA cases. It is concluded that the selective use of well-chos en panels of antibodies can be very helpful in resolving diagnostic di fficulties in cytologic specimens. In particular, ICC may be an invalu able aid to the diagnosis of difficult serous effusion specimens and i n the sub-typing of poorly differentiated malignancy.