Immunohistochemistry of Thymoma, [Pathology] Atlas of Immunohistochemistry of Thymoma, Atlas of Mediastinal Pathology
The diagnosis of thymomas is mainly predicated on identifying their characteristic features on routine microscopy using hematoxylin and eosin (H&E)-stained tissue sections. In some instances, however, the use of ancillary techniques can be of help in establishing the diagnosis. Table 2.3 shows some of the most common immunostaining patterns used in thymomas.
Table 2.3 Most common immunohistochemical stains in diagnosis of thymoma
+++ strong positivity in the majority of the cells, ++ strong positivity in
many of the cells, + focal positivity in some cells, +/- may show focal
positivity or negative, - negative staining in the tumor cells
Fig. 2.95 Immunohistochemical staining in lymphocyte-rich spindle-cell
thymoma (WHO type AB): (a) keratin staining shows diffuse cytoplasmic
positivity (AE1/AE3); (b) p63 testing shows strong nuclear positivity in
the spindle cells in type AB thymoma; notice the negative small lymphocytes
in the background and the oval shape of the stained nuclei; (c) bcl-2
positivity is seen in the epithelial cells in type AB thymoma. Bcl-2 is often
positive in spindle-cell thymoma but does not stain the B types. This can
be a useful adjunct for separating lymphocyte-rich thymoma (type B1)
from lymphocyte-rich spindle-cell thymoma (WHO type AB)
Fig. 2.96 (a) Keratin staining in lymphocyte-rich thymoma (WHO
type B1); (b) p63 nuclear staining in lymphocyte-rich thymoma (type
B1) shows scattered positive nuclei surrounded by numerous negativestaining
small lymphocytes; (c) CD1a staining in type B1 thymoma
highlights a dense population of immature thymocytes
Fig. 2.97 Immunohistochemical staining in atypical thymoma (WHO
type B3): (a) p63 nuclear staining labels virtually all the epithelial cells;
(b) CD117 positivity is seen in scattered epithelial cells; (c) Ki-67
proliferation marker shows scattered nuclear positivity in ~15 % of the
epithelial cells. Atypical thymomas (WHO type B3) always display an
increased proliferation rate compared with other types of thymoma
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