Special Stains - Old School Cool
Special stains highlight specific cellular components, aiding diagnosis.
| Stain | Detects | Applications |
|---|---|---|
| PAS | Glycogen, neutral mucins | AdenoCa (mucin), fungi, glycogenoses |
| Mucicarmine | Epithelial mucin | AdenoCa (GIT, breast), signet cells |
| Oil Red O | Lipids (fresh) | Fat embolism, liposarcoma |
| Prussian Blue | Ferric iron ($Fe^{3+}$) | Hemosiderin, asbestos bodies |
| Alcian Blue | Acid mucins (pH specific) | Mesothelioma (pH 2.5), AdenoCa (pH 1.0) |
| Fontana-Masson | Melanin, argentaffin granules | Melanoma, neuroendocrine tumors |
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Immunocytochemistry - Antibody Avengers
Principle: Specific antigen-antibody binding, visualized by chromogen or fluorescence. Essential for precise cell/tumor typing.
Common ICC Markers & Significance:
| Category | Markers | Key Use / Associations |
|---|---|---|
| Epithelial | Pan-CK, CK7, CK20, EMA, p63, p40 | Carcinomas |
| Mesenchymal | Vimentin, Desmin, SMA, S100 | Sarcomas; Melanoma, Neural (S100) |
| Neuroendocrine | Chromogranin, Synaptophysin, CD56 | Neuroendocrine Tumors (NETs), Small Cell Carcinoma |
| Lymphoid | LCA/CD45, CD20 (B), CD3 (T), MPO | Lymphomas, Leukemias |
| Site-Specific | TTF-1 (Lung/Thyroid), Napsin A (Lung), CDX2 (Colon), GATA3 (Breast/Uro), PAX8 (Renal/Ovary) | Metastasis workup |
| Proliferation | Ki-67 | Proliferative index (e.g., >20% often high grade) |
- Diagnosis: Differentiating poorly differentiated tumors (carcinoma vs sarcoma vs lymphoma).
- Subtyping tumors (e.g., adenocarcinoma vs squamous).
- Identify primary site of metastasis.
- Prognostic/Predictive markers (ER/PR, Her2/neu, PD-L1).
📌 CK7/CK20 Patterns:
- CK7+/CK20-: Lung, Breast, Gynae.
- CK7-/CK20+: Colorectal, Merkel.
- CK7+/CK20+: Urothelial, Pancreatobiliary.
Algorithm for Undifferentiated Tumors:
Pitfalls: Cross-reactivity, improper fixation, interpretation errors.
⭐ > A panel of Calretinin, WT-1, CK5/6 (+ve) and MOC-31, Ber-EP4, CEA (-ve) is characteristic for mesothelioma.
Molecular Diagnostics - Gene Genies
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Flow Cytometry & Others - Cell Sorting & More
- Flow Cytometry (FC):
- Principle: Light scatter & fluorescence analysis of antibody-tagged cells in suspension.
- Applications: Immunophenotyping (leukemia/lymphoma in fluids, FNA); DNA ploidy (prognosis).
- Advantages: Rapid, quantitative, multi-parameter cell analysis.
- Limitations: Fresh/unfixed sample, viable cells needed; no architectural detail.
- Electron Microscopy (EM):
- Principle: Ultrastructural detail via electron beams.
- Uses: Limited; confirms neurosecretory granules, viruses, ciliary structures.
⭐ Flow cytometry: Gold standard for lineage & clonality in suspected lymphomas (FNA/fluids).
High‑Yield Points - ⚡ Biggest Takeaways
- Immunocytochemistry (ICC): Crucial for tumor typing, origin, and prognostic/predictive markers.
- Flow Cytometry: Key for leukemia/lymphoma diagnosis and classification from aspirates.
- Molecular Tests (FISH, PCR): Detect specific genetic alterations (translocations, mutations) for diagnosis/therapy.
- Cell Blocks: Provide tissue architecture; vital for multiple ancillary studies (ICC, molecular).
- Special Stains: Identify specific substances like mucin, glycogen, or microorganisms.
- Liquid-Based Cytology (LBC): Improves sample quality, enables multiple tests from one sample.
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