Immunohistochemistry (IHC | F) Flashcards
Provide a sample case (in relation to the application of IHC) and provide the clinical impression for the said case
A pt (male; 39 yo) has the ff:
1) Bilateral pleural effusion
2) Enlarged mediastinal lymph nodes
3) Enlarged paraaortic and retrocrural lymph nodes
Clinical impression: Bilateral Pleural Effusion secondary to Non-Hodgkin’s Lymphoma
What are the immunostains that are suggested by the patho to be done in relation to their initial dx (w/ regards to the sample case) w/c is undifferentiated carcinoma vs. non-Hodgkin’s lymphoma?
Immunostain for:
1) Cytokeratin
2) Leukocyte common antigen (LCA)
What are the 2 methods for immunohistochemical detection methods?
Can use:
1) Fluorescent probes
2) Enzymatic methods
What is the principle of immunofluorescence technique?
This is where fluorescent substances (/ fluorophores) are used
What is the principle of immunoenzyme technique?
Through enzymatic conversion (often by horseradish peroxidase [HRP]) of a soluble substrate (chromogen) into a non-soluble and colorful rxn product
What are the steps for IHC (for enzymatic method)?
1) Tissue sections
2) Ag retrieval
3) Blocking endogenous enzymes
4) Secondary Ab
5) Primary Ab
6) Microscopy observation
7) Chromogen substrate
8) Counterstain
9) Mounting
10) Microscopy observation (by the patho)
What are the applications of IHC in terms of lab dx of CA (immunocytochemistry)?
1) Application of immunochemical rxns on tissue sections / cell preparations
2) An ancillary technique employed in the dx of tumors
3) Demonstration of Ags (w/c are markers of certain tumors)
What is the general principle of IHC?
Ag (protein trying to be detected) is present + primary Ab (attaches to the epitope) = Ag-Ab rxn
What are the common applications of IHC?
1) Categorization of “undifferentiated” malignant tumors
2) Detection of Ags of potential prognostic / therapeutic importance
a. ER / PR (estrogen receptor / progesterone receptor)
b. Oncogene and tumor suppressor gene products
3) Determine the site of origin of metastatic tumors
4) Subclassification of tumors in various organ systems and tissue compartments
5) Categorization of leukemias and lymphomas
6) Distinction between adenocarcinoma (CK 8-18+) and mesothelioma (CK 8-18 -)
What are the staining patterns in IHC?
1) AE1/AE3: shows (+) tumor cell staining
a. For small cell carcinoma
b. For IHC
2) Chromogranin: shows (+) cytoplasmic staining
a. For small cell carcinoma
b. For IHC
3) CD56: (+) w/ a membranous pattern
a. For small cell carcinoma
b. For IHC
4) TTF-1: shows diffuse (+) nuclear staining
a. For small cell carcinoma
b. For IHC
5) Ki-67 (panel d): shows a high proliferation rate w/ almost 100% tumor cell staining
a. For small cell carcinoma
b. For IHC
What is the screening algorithm for the differentiation and categorization of malignant tumors?
1) The patho must 1st develop a differential dx
2) Differential dx depends on the tumor’s:
a. Histologic appearance
b. Anatomic location
c. Clinical setting
What is primary screening panel and what is its use?
It is the “first-line” marker / Ab used to categorize undifferentiated malignant tumors accdg to histologic lineage
What are the usual components of primary screening panel (for undifferentiated CAs)?
1) Pancytokeratin
2) LCA
3) S-100
4) Placental alkaline phosphatase (PLAP)
5) Synaptophysin
6) Vimentin
Pancytokeratin is used for what?
Carcinoma
LCA is used for what?
Lymphomas
PLAP is used for what?
Germ cell tumor
Synaptophysin is used for what?
Neuroendocrine (chromogranin)
Vimentin is used for what?
Sarcoma (desmin and actin [can be added if pt has enough resources: for the differential dx to be more sure])
What is the fxn of secondary screening panel?
To classify tumors accdg to histologic type
Provide an ex. of the application of secondary screening panel (for lymphomas)
Pt is (+) for LCA -> it should be differentiated if it is CD 20 (+) / CD 3 (+) -> if it is CD 20 (+), it is a B cell type; if it is CD 3 (+), it is a T cell type
Provide another ex. of the application of secondary screening panel (for anaplastic and super undifferentiated lymphomas)
Pt is (+) for LCA -> differentiate if pt is CD 20 (+) / CD 3 (+) -> if pt is CD 20 (+): it is B cell and/or lymphocyte predominant HL | if pt is CD 3 (+): it is T cell
But if pt is (-) for LCA -> the differential dx can be: 1) lymphoblastic lymphoma, 2) large cell anaplastic lymphoma, 3) immunoblastic lymphoma, 4) Hodgkin’s lymphoma (RS: CD15 [+]); except lymphocyte predominant (LCA [+])
What is the relationship between pancytokeratin and LCA (in terms of dx)?
If pancytokeratin is (-) and LCA is (+): it is assured that it is lymphoma
But if both pancytokeratin and LCA are (-): tertiary screening panel is done
Pancytokeratin: for carcinoma
LCA: for lymphoma
What is the differential workup if both cytokeratin and LCA are (-)?
Cytokeratin and LCA are both (-) -> can be 1) anaplastic lymphoma, 2) immunoblastic lymphoma, and/or 3) lymphoblastic lymphoma -> anaplastic lymphoma: CD 30 (+) | immunoblastic lymphoma: CD 20 (+) | lymphoblastic lymphoma: B-cell (CD 19 [+]) or T-cell (CD 3 [+])
True or False
IHC is only an adjunct to dx
True
True or False
Results (of / via IHC) must not be interpreted in the context of other findings (such as routine H & E sections and the clinical setting)
False, because results (of / via IHC) must be interpreted in the context of other findings (such as routine H & E sections and the clinical setting)
