DNA Sequencing and Antibody Gene Microarray

The human genome can now be manipulated to such an extent that single nucleic acid substitutions are es

FIGURE 12.10. Alternative embedding and staining techniques: (A) paraffin-embedded H&E stain, (B) paraffin-embedded IHC staining, (C) celloidin embedding, (D) transmission electron microscopy, and (E) scanning electron microscopy.

chapter 12: orbital biopsy MALIGNANT PLEOMORPHIC TUMORS

chapter 12: orbital biopsy MALIGNANT PLEOMORPHIC TUMORS

FIGURE 12.11. Immunohistochemi-cal algorithm for identifying malignant pleomorphic tumors including melanoma, liposarcoma, spindle cell squamous cell carcinoma (SCC), leiomyosarcoma, rhabdomyosarcoma, malignant fibrous histiocytoma (MFH), and malignant peripheral nerve tumors (MPNST).

sentially a routine, albeit highly complex, laboratory testing method. The relatively new technology of high performance liquid chromatography (HPLC) makes possible the anatomic sequencing of the DNA (or RNA) isolated from intact cells. This in turn permits specific, single nucleotide substitutions, deletions, or additions to be uniquely identified.63-66 An example of such an analysis is shown in Figure 12.16.

The antibody microarray is simply a derivation of the gene microarray.67 In the latter, specific gene sequences are applied to the surface of a glass slide. The number of DNA sequences generally number from

1000 to 10,000 per slide. The patient's single-stranded DNA sequences are then applied to the slide and the various strands allowed to anneal. The resulting signal is analyzed, and the diagnosis is made. In the case of the antibody microarray, specific antibodies are applied to the surface of the slide and then the patient cells are poured over the surface. The specific antibodies retain cells depending on the expression of the appropriate antigens on the cell surface.

Almost all orbital and adnexal biopsies are small, and routine morphologic findings may not be sufficient for diagnosis.68,69 The utilization of ancillary

FIGURE 12.12. Immunohistochemical algorithm for differential diagnosis of small blue round cell tumors.
FIGURE 12.13. Immunohistochemical algorithm for differential diagnosis of poorly differentiated spindle cell tumors.

testing has improved the diagnostic accuracy, particularly for distinguishing reactive lymphoid proliferations from lymphoma. Recent studies indicate that lymphoid neoplasms can be accurately distinguished from reactive lymphoproliferative and inflammatory lesions by a combination of routine light microscopy IHC, and FC.68-70

In other tumors of the orbit, including carcinomas, sarcomas, and secondary and metastatic lesions, FC immunotyping rarely plays a role in diagnosis; rather, IHC, molecular studies, and cytogenetic analysis are often the primary adjunct to light microscopic examination. Neoplasms that are not amenable to FC analysis are subjected to routine procedures for paraffin-embedded tissues, given earlier in Table 12.3.

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