In order to make a diagnosis, a microscopic examination of the tissue sample is performed by a specially trained physician called a pathologist.
Before examination, the sample is sent to the histopathology laboratory, where it will go through a multi-step process: It starts by placing the tissue in a fixative that will prevent any decay. Next it will be dehydrated and embedded in paraffin wax to preserve the cells and structure.
Once the tissue has been embedded, the paraffin wax block with the embedded tissue is cut into very thin slices – thinner than a fraction of a human hair. These thin slices are mounted on a glass slide, the tissue is deparaffinised and then stained with different dyes to identify distinct cellular structures and special features of the tumour.
The routine staining process in Diagnostic Pathology is called hematoxylin and eosin (H&E) which stains different cells and structures making them visible under a microscope. The pathologist can then detect irregular cell growth and determine the next step of treatment.
In most cases the diagnosis can be obtained by H&E alone, sometimes additional special stainings are needed. Such special stainings can for example detect certain amounts of protein that indicate the likelihood of a patient to respond to certain cancer treatments.
Immunohistochemistry (IHC) test
In IHC tests a diagnostic antibody binds to a certain target protein in cells or on cell membranes on the tissue slides.
If the target protein is present in or on the tumour cells, the diagnostic antibody is able to recognise and bind to this protein (key-lock-principle). This biophysical interaction can be visualised by colour reaction on the tissue slide and assessed under the microscope.
This is an important factor to help determine the type of drug therapy the patient will respond to.
If necessary, gene status may need to be determined by testing called in situ hybridisation. This test can be seen by fluorescence (FISH) or newer techniques that utilise a light microscope.
New specialised tests are being developed to identify gene status for many different cancers.
Fluorescent in situ hybridization (FISH)
This test uses fluorescent pieces of DNA that specifically stick to copies of the HER2/neu gene in cells, which can then be counted under a special microscope.
Newer test methods are now becoming available as well. These chromogenic tests such as SISH, use a routine microscope.
The journey to a tissue biopsy
Cancer testing: The journey to a tissue biopsy.
See our 11-step process