​immunohistochemistry General concepts: 

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• Immunohistochemistry (IHC) describes the process of staining a piece of tissue with various markers to highlight a particular cell type. 

• Uses:

  • Further classify a poorly differentiated tumor​ (carcinoma vs. lymphoma vs. melanoma etc)

  • Help determine the primary location of a tumor in a patient who presents only with metastatic disease (lung, colon, breast, prostate etc)

  • Distinguish between in-situ vs. invasive lesions by determining whether the tumor invades beyond the basement membrane, basal cell layer or a capsule.

  • Assess the proliferative rate (Ki-67 stain) and establish the overall prognosis (various genetic mutations identifiable).

  • Predict whether a tumor will respond to a particular therapy by determining whether the a mutation targeted by the drug is present.

  • Detect tiny, single, metastatic tumor cells in a lymph node (such as in melanoma or breast cancer cases).

  • Identify viral or other infectious organisms.

• Tumors typically stain in a very particular way, BUTTTTT "tumors don't read the textbooks" which means not every single squamous cell carcinoma will stain positive with a cytokeratin.

• Thus, although IHC can aid in the diagnosis, the morphology seen on routine H&E stain trumps IHC nearly every time. Go by morphology and use the IHC stains as pieces of the puzzle to help you come to the most likely diagnosis!! 

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​Commonly used stains