Immunohistochemistry and molecular tissue methods
Immunohistochemistry localizes a target using an antibody and a detection system. The apparent signal depends on fixation, processing, antigen accessibility, antibody specificity, detection chemistry and observation. A strongly colored slide is not automatically a specific result, and a negative result is not interpretable without appropriate evidence that the assay worked on suitable material.
Antigen retrieval can improve access to targets affected by fixation, using heat or other validated approaches. Different antibodies and tissues need different conditions. More intense retrieval is not always better: it can damage sections or alter background. The complete validated assay, including relevant controls, should govern the procedure rather than transferring one buffer and temperature to every marker.
Detection chemistry creates particular compatibility questions. HRP-based methods can produce a visible chromogen, but endogenous enzyme activity and nonspecific binding can contribute to background. Biotin-free polymer systems avoid the specific endogenous-biotin mechanism of older biotin-dependent designs, not every possible false-positive reaction. A chromogen’s solvent compatibility determines how the section can be finished, so a mounting sequence suitable for one reaction product may remove another.
Interpret location and pattern as well as intensity. A lineage-associated marker is not universally present in every tumor of that lineage or absent from every other tumor. Panels, morphology and clinical information are therefore important. Proliferation indices depend on sampling, counting and assay conditions and are not automatically a direct tumor doubling time. Disease-specific predictive-marker criteria must come from current validated guidance rather than a generic stain-color rule.
Molecular methods detect selected nucleic-acid targets through amplification or hybridization. Probe or primer specificity, positive controls, negative controls, contamination prevention and sample quality matter. A no-template signal raises a different concern from an extraction-control failure. A fluorescence image requires its appropriate optical system and controls. Report the result justified by the actual method and role, and preserve limitations. Written practice cannot establish competence in wet-lab performance, diagnostic scoring, current national accreditation requirements or clinical treatment selection.