Page 9 - Clinical Connections - Summer 2024
P. 9

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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