Immunocytochemistry ICC

Use of ICC for detecting antigens in tissue sections for diagnostic purposes is now routine. Preservation of the antigen(s) and validation of antibodies are critical technical prerequisites, whereas interpretation of results supplemented by positive and negative controls are the histopathologist's responsibility. Many antibodies (most of them monoclonal) are now available, working on paraffin-embedded material with/without antigen retrieval. Targets are:

♦ Structural antigens (e.g. intermediate filaments).

♦ Matrix antigens.

♦ Functional antigens (secretory products).

♦ Lineage antigens (immunoglobulins).

♦ Membrane-bound antigens (receptors, glycoproteins).

♦ Miscellaneous cell constituents.

Rarely does a single antibody afford a specific diagnosis; mostly a small panel of antibodies yields more reliable information. Anaplastic tumours whose differential diagnoses include carcinomas, large-cell lymphomas, sarcomas, and melanoma, and small round-cell tumours in childhood which include neuroblastoma, the Ewing's sarcoma family (including PNET), lymphomas, and some rhabdomyosarcomas, are particular targets for immunocytochemical scrutiny.

A second level of investigation is represented by the array of malignant lymphomas, both of Hodgkin's and non-Hodgkin type. Their categorization on the basis of the recent REAL classification is facilitated by the antibodies that offer a cluster designation (CD).

An additional use of ICC is tumour staging consisting of a search of malignant cells by means of appropriate antibodies in lymph nodes, bone marrow, in lumina of peritumoral vessels, and at surgical resection margins.

Markers of proliferation, diagnostic cell products, and expressions of (onco)-gene protein products are also targets of the immunocyto-chemical diagnostic approach. Antibodies against chimeric fusion proteins are now available; the first example was an anti-p80 (chimeric NPM-ALK protein) antibody to detect t(2;5) (p23;q35) in anaplastic large-cell lymphoma.

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