Useful immunohistochemical markers of tumor differentiation

Abstract

Immunohistochemistry (IHC) has been somewhat underutilized in the practice of toxicological pathology but can be a valuable tool for the evaluation of rodent neoplasms, both in a diagnostic and an investigational role. Determining an exact tumor type using standard hematoxylin and eosin (H&E) staining of formalin-fixed tissues can be challenging, especially with metastatic and/or poorly differentiated tumors. Successful IHC is dependent on many factors, including species and tissue type, type and duration of fixation, quality fresh or frozen sectioning, and antibody specificity. The initial approach of most tumor diagnosis IHC applications is distinguishing epithelial from mesenchymal differentiation using vimentin and cytokeratin markers, although false-negative and/or false-positive results may occur. Experimentally, IHC can be employed to investigate the earliest changes in transformed tissues, identifying cellular changes not normally visible with H&E. Individual markers for proliferation, apoptosis, and specific tumor proteins can be used to help distinguish hyperplasia from neoplasia and determine specific tumor origin/type. IHC provides a relatively rapid and simple method to better determine the origin of neoplastic tissue or investigate the behavior or progression of a given neoplasm. Several experimental and diagnostic examples will be presented to illustrate the utility of IHC as a supplement to standard staining techniques.

Figure 1

IHC presentation of positive control tissues for selected markers. All are at 10X magnification, except for Figure 1B at 20X magnification. (A) Pancytokeratin staining of the epithelial tissues of the nonglandular stomach. (B) Vimentin staining of the glomeruli and adjacent perirenal vasculature. (C) CD79a staining of the spleen. Note presence of B lymphocytes in the marginal zone and follicles of the white pulp. (D) ED2 staining of the macrophages in the red pulp of this rat spleen.

Figure 2

Comparative H&E staining of potential erythroleukemia in a negative control rat spleen, compared to confirmed MCL and EMH in the spleen of two other control rats. Figures A, C, and E are at 10X magnification; Figures B, D, and E are at 40X. (A, B) Case slide—Disruption of normal architecture, large numbers of nucleated erythrocytes and large polygonal cells. (C, D) MCL—More severe disruption of splenic architecture, large numbers of mononuclear neoplastic cells. (E, F) EMH—Normal splenic architecture, with multifocal aggregates of hematopoietic cells and accumulated yellow iron pigment.

Figure 3

Comparative Hgb staining of potential erythroleukemia in a negative control rat spleen, compared to confirmed MCL and EMH in the spleen of two other control rats. Figures A, C, and E are at 10X magnification; Figures B, D, and E are at 40X. (A, B) Case slide—Most neoplastic cells are positive for Hgb. (C, D) MCL—Hgb positive cells are uncommon, other than some nonspecific light staining. (E, F) EMH—Aggregates of Hgb positive cells match up with the multifocal hematopoietic tissue seen with H&E staining in Figure 2.

Figure 4

Comparative PAX-5 staining of potential erythroleukemia in a negative control rat spleen, compared to known MCL and EMH in the spleen of two other control rats. Figures A, C, and E are at 10X magnification; Figures B, D, and E are at 40X. (A, B) Case slide—All neoplastic cells are negative for PAX-5. (C, D) MCL—PAX-5 positive cells are present as infrequent loose aggregates. (E, F) EMH—Multifocal dense accumulations of PAX-5 positive cells match up with known B lymphocyte areas in the white pulp of the spleen with normal architecture.

Figure 5

β-catenin staining of hepatocellular carcinoma, 10X magnification. Note the focal transformation of positive stain from the relatively normal membranous pattern to a potentially more malignant cytoplasmic and nuclear pattern.