Page 9 - Clinical Connections - Summer 2024

Pathology
USEFULNESS OF IMMUNOHISTOCHEMISTRY
IN SURGICAL ONCOPATHOLOGY

Bernat Martí-García, Lecturer in Farm Animal Pathology, Simon L. Priestnall, Head of the Department
of Pathobiology and Population Sciences, and Alejandro Suárez-Bonnet, Senior Lecturer in
Comparative Pathology

s medical care of our pets is In this context, IHC can help to pave the But what does IHC really entail? IHC is
improving, their life expectancy way towards more personalised or targeted the use of specific antibodies that label
A is longer and cancer prevalence treatments for cancers in our companion specific antigens of tumoral cells which
increases. An accurate and early diagnosis animals. For instance, two commonly used then can be highlighted and visualised by
of cancer can be challenging due to the markers with prognostic significance in using colour-emitting substances (so-called
multifactorial origin of this disease, which dogs are Ki67 and Kit. Ki67 is a marker of chromogens).
exhibits many faces, and its unspecific actively dividing cells and is often used as The primary antibody, which will directly
clinical signs. Surgical biopsies, with a prognostic factor for canine cutaneous attach to the tissue antigen, is usually
complete or partial removal of the tumour, mast cell tumours (CMT) by quantitatively commercially available, and, in veterinary
are essential for diagnostic purposes and assessing the tumoral replication activity medicine, these are most often obtained
complete removal is occasionally the only (Figure 1). from mice, rabbits or goats that have been
feasible treatment. exposed to antigens of human origin.
Once the formalin fixed tissue is Fortunately, most antibodies have a wide
submitted to the laboratory, it is processed cross-reactivity among species and thus do
for routine histopathological evaluation bind to and label antigens in most common
using Haematoxylin and Eosin (H&E) domestic species.
staining, which is the ‘bread and butter’ for Once bound to the specific target antigen
histopathologists. in the tissue, a second antibody which
Microscopic evaluation of H&E slides contains an enzyme label is applied. Finally,
allows pathologists to provide a diagnosis the chromogen, usually diaminobenzidine
of a given tumour based around one of the (DAB) or ethylcarbazole (AEC), is applied,
following categories: round cell tumours which produces a colour change. This
(lymphoma, histiocytic sarcoma or mast Figure 1. Ki67 immunohistochemistry labels colour (brown with DAB and red with AEC)
actively replicating cells. In this image from a
cell tumours, among others), sarcomas colon adenoma, neoplastic cells are strongly can then be visualised under standard light
(fibrosarcoma, haemangiosarcoma, positive, while non-cancerous cells are microscopy.
rhabdo- or leiomyosarcoma, among others) negative Finally, a counterstain (haematoxylin,
or epithelial tumours (squamous cell dark blue), is applied so that the overall
carcinoma, transitional cell carcinoma or The receptor tyrosine kinase (Kit) is tissue architecture is still appreciable. For
adenocarcinomas, among others). expressed in mast cells and other cell this reason, IHC is sometimes known by
A definitive diagnosis is achieved most types, such as haematopoietic stem cells, pathologists as the ‘red, brown, and blue
of the time based on H&E stained sections interstitial cells of Cajal (the cell of origin technique’ and, most laboratories now use
alone. However, immunohistochemistry for gastrointestinal stromal tumours) and an autostainer for routine diagnostic work,
(IHC) is required in some instances to reach melanocytes. Tumoural mast cells can show allowing performance of dozens of IHCs per
a definitive diagnosis, given the marked aberrant KIT expression (e.g., a perinuclear week.
dedifferentiation (i.e. anaplasia) of the pattern, aka pattern II) which is correlated Our turnaround time for all routine
tumoral cells or the morphological similarity with increased cell proliferation and a higher samples is 48 hours from receipt of the
with other neoplasms, e.g. melanoma with histological grade of canine CMT (Figure 2). specimen into the laboratory. The report
epithelial tumours. contains a full ‘board-style’ histological
description, diagnosis and comment, which
Contextualisation is tailored specifically to the case.
Before recommending an IHC analysis,
however, it is highly recommended that
the clinician and the pathologist discuss
the case to fully contextualise the clinical
signs and findings with the histopathological
features. IHC can also help to inform the
clinical prognosis and guide the therapeutic Figure 2. KIT immunohistochemistry reveals
a pattern II in a canine cutaneous mast
approach and prognosis of a given neoplasia cell tumour, which is associated with a
for an individual animal. higher histological grade and a higher cell
proliferation rate
For the Diagnostic Pathology Service,
please call:01707 666 208
Email:
diagnosticlabs@rvc.ac.uk

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