BCL-2 immunostain in follicular lymphoma. These images illustrate the typical staining of (A) neoplastic follicles in follicular lymphoma as compared to (B) benign, reactive germinal centers. Note that in follicular lymphoma neoplastic centrocytes equivalent to neoplastic germinal center cells overexpress the anti-apoptotic protein BCL-2 (arrows), whereas in reactive germinal center, no appreciable staining is noted (arrow), but mantle zone cells surrounding the germinal center (asterisk) are positive. In follicular lymphoma, the overexpression of BCL-2 can be attributed in about 80% to 85% of cases to a translocation involving the immunoglobulin heavy chain locus on chromosome 14q32 and the BCL-2 gene locus on chromosome 18q21, resulting in a constitutive overexpression of this protein.
ALK-1 immunostain in anaplastic large cell lymphoma. The images illustrate (A) neoplastic cells in a case of ALK-1-positive anaplastic large cell lymphoma (ALCL) in which the biopsy is stained with H&E. Note the preserved germinal center in the upper right quadrant of the photomicrograph (arrow). ALCL involves nodes in a sinusoidal pattern that mimics metastatic tumor. (B) An ALK-1 positive (anaplastic lymphoma kinase-1) immunohistochemical stain of the biopsy is shown. In ALCL, a chromosomal translocation occurs involving the ALK-1 gene on chromosome 2p23 and the nucleophosmin gene on 5q35 occurs. A number of variant translocations have also been described. The overexpression of ALK-1 is not seen in all cases of ALCL. Expression of ALK-1 has been correlated with a better survival using current chemotherapy protocols.