An advanced pathology examination in which specific proteins in tissue samples are visualized in color by an antibody-antigen reaction, used in cancer subtyping and targeted therapy planning.
Indication
- Determination of tumor origin (epithelial, mesenchymal, lymphoid)
- ER, PR, HER2, and Ki-67 receptor/proliferation evaluation in breast cancer
- Markers such as CD20, CD3, CD30, BCL2 for lymphoma subtyping
- Origin determination in the workup of carcinoma of unknown primary
- Micrometastasis screening (especially in sentinel lymph nodes)
- Identification of candidates for targeted therapy (e.g., PD-L1, ALK, ROS1)
- Special markers for differential diagnosis of inflammatory/infectious diseases
Preparation
- Standard formalin fixation (24-48 hours) and paraffin embedding
- Communication of clinical information (tumor type, location, prior treatments) to the pathologist
- Selection of the target antibody panel by the pathologist according to the clinical question
- Preparation of a calibrated automated IHC instrument and appropriate positive-negative controls
How it's performed
- A 3-4 micron section is taken from the paraffin block and placed on a positively charged slide
- Deparaffinization and antigen retrieval (by heat or enzyme) are performed
- Endogenous peroxidase blockade and protein blockade are applied
- The primary antibody (e.g., ER, HER2, CD20) is applied to the slide and incubated
- The reaction is visualized using a secondary antibody and chromogen (DAB or AEC)
- Counterstaining is performed with hematoxylin; the pathologist evaluates staining intensity and distribution (e.g., 0/1+/2+/3+ score for HER2, Ki-67 percentage)
Post-procedure
- IHC results are added to the routine pathology report and typically completed within 5-10 business days
- Results are integrated into the treatment plan together with the oncologist and surgeon
- FISH/CISH confirmation is recommended in HER2 2+ cases
- In patients started on targeted therapy, treatment response is monitored through clinical follow-up
- Equivocal staining may be re-examined or evaluated with an alternative clone
Risks
- False-negative/positive results when fixation duration is insufficient or excessive
- Result variability arising from differences in antibody clone, manufacturer, and protocol
- Difficulty in clinical decision-making with borderline results
- If tissue sample is insufficient, the full panel may not be applicable, and re-sampling may be required
FAQ
When is immunohistochemistry requested?
It is performed when the pathologist deems it necessary to confirm tumor type, perform subtyping, and identify candidacy for targeted therapy.
What do ER, PR, and HER2 results mean?
These markers especially guide treatment selection in breast cancer: hormone receptor positivity indicates potential response to endocrine therapy, while HER2 positivity indicates potential response to targeted drugs.
What does a high Ki-67 indicate?
Ki-67 is a marker reflecting cell proliferation rate. High values are generally associated with a more aggressive course, but it is not a sole determining factor.
How long does an IHC result take?
A routine IHC panel is generally completed within 5-10 business days. The duration may be extended for additional antibody requests.
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