Role of Immunohistochemical Analysis Immunohistochemical stains are peroxidase-labeled antibodies against specific tumor antigens that are used to define tumor lineage. The number of available immunohistochemical stains is ever-increasing. However, in CUP cases, more is not necessarily better, and immunohistochemical stains should be used in conjunction with the patient's clinical presentation and imaging studies to select the best therapy. Communication between the clinician and pathologist is essential. No stain is 100% specific, and over-interpretation should be avoided. PSA and thyroglobulin tissue markers, which are positive in prostate and thyroid cancer, respectively, are the most specific of the current marker panel. However, these cancers rarely present as CUP, so the yield. | Chapter 095. Carcinoma of Unknown Primary Part 3 Role of Immunohistochemical Analysis Immunohistochemical stains are peroxidase-labeled antibodies against specific tumor antigens that are used to define tumor lineage. The number of available immunohistochemical stains is ever-increasing. However in CUP cases more is not necessarily better and immunohistochemical stains should be used in conjunction with the patient s clinical presentation and imaging studies to select the best therapy. Communication between the clinician and pathologist is essential. No stain is 100 specific and over-interpretation should be avoided. PSA and thyroglobulin tissue markers which are positive in prostate and thyroid cancer respectively are the most specific of the current marker panel. However these cancers rarely present as CUP so the yield of these tests may be low. Fig. 95-1 delineates a simple algorithm for immunohistochemical staining in CUP cases. Table 95-2 lists additional tests that may be useful to further define the tumor lineage. A more comprehensive algorithm may improve the diagnostic accuracy but can make the process complex. With the use of immunohistochemical markers electron microscopic analysis which is timeconsuming and expensive is rarely needed. Figure 95-1 lAortii Fiua . K tp- r t L. BraunTfcW L. Hâuiir VL. Lcr-p - DL. Jamaipn X L-Plcflc-ô J AfcaÿJu of 5 Tth EÆt-Mii h p i m - . ji t - . . - - ----- O Th Hr iijT-Hdl Corr pBni i. Ir-c aji pqhtii r n v d. Approach to cytokeratin CK7 and CK20 markers used in CUP. Table 95-2 Additional Immunohistochemical Stains Useful in the Diagnosis of CUP Tissue Marker Diagnosis Estrogen and progesterone receptors Breast cancer BRST-1 Breast cancer Gross cystic disease fibrous protein- 15 Breast .
