Page 4 - Clinical Connections - Summer 2023
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RVC RESEARCH    STUDY    VETERINARY SERVICES       RVC.AC.UK
         Oncology
        SENTINEL LYMPH NODE MAPPING –
        LEADING THE WAY IN ONCOLOGY


        Andy Yale, Lecturer in Veterinary Oncology

              ancer is a common disease in   the primary tumour or scar, followed by an
              older  cats  and  dogs  but,  as  more   imaging technique to visualise the exact
        C advanced diagnostic and treatment   LN(s) that drain the patient’s tumour. These
        modalities become available, the prognosis   ‘sentinel’ LNs are then sampled to check for
        and quality of life of many pets with cancer   metastasis.
        can be good.                          This means LN sampling can be much
          Sentinel  lymph  node  (SLN)  mapping  is   more  specific  and  personalised,  both
        a diagnostic tool commonplace in human   increasing the accuracy of metastasis
        oncology  and  developing  in  veterinary   detection  and  reducing  patient  morbidity.
        oncology. It increases the accuracy of   There are a variety of techniques available   Beetle, following revision surgery (requiring an
        detection of metastatic disease whilst   for SLN mapping, although CT and   advancement flap) of her incompletely excised
        minimising patient morbidity.       ultrasound-based techniques are most   MCT of the dorsal head, and SLN extirpation
          With  increased  detection  of  metastasis,   common in veterinary oncology.
        more  patients  can  be  offered  additional                            were  identified  (left  parotid  LN,  bilateral
        therapies that may not have otherwise been   Case study – Beetle        mandibular LNs). Cytology of these did not
        considered – thus improving outcomes.   Beetle,  a  nine-year  11-month  female   identify MCT metastasis but, as cytology
          Cancer commonly spreads to lymph   neutered  Labrador,  was  seen  by  RVC   can miss MCT LN metastasis in around
        nodes  (LNs)  and,  historically,  assessment   Small Animal Referrals’ Oncology Service   25%  of  cases,  the  SLNs  were  extirpated
        for LN spread would be based on cytology   in 2021. Beetle had an incompletely excised   for  histopathology  at  the  time  of  revision
        of  LNs  that  are  anatomically  closest  to   low-grade   (Kiupel),   intermediate-grade   surgery for the incompletely excised MCT.
        the  tumour, and/or regional  LNs  that are   (Patnaik)  mast  cell  tumour  (MCT)  on  the   Histopathology  identified  the  parotid
        enlarged. However, there are limitations   head, situated midline above both eyes.   LN as pre-metastatic, with no evidence of
        to this approach as tumours can develop   Despite being low- to intermediate-grade,   metastasis  in  either  mandibular  LN.  Prior
        unpredictable  lymphatic  drainage  patterns   the  MCT  had  a  high  Ki67  index  (>1.8%)   cytology did not identify evidence of spread.
        – meaning they may drain to LNs distant to   – indicating a more aggressive biologic   Beetle completed a course of adjuvant
        the tumour location, bypassing more local   behaviour.  Therefore, thorough staging   lomustine  chemotherapy  and  has  been
        LNs.                                prior to  revision surgery  and adjuvant   doing well since with no evidence of MCT
          Additionally, many normal-sized LNs can   chemotherapy was discussed.   recurrence or metastasis.
        still harbour metastatic disease. Thoroughly   Staging without techniques such as SLN
        assessing for LN metastasis without specific   mapping would have involved sampling   Benefits across species
        techniques,  such  as  SLN,  mapping  would   many LNs as lymphatic drainage patterns   As SLN mapping and biopsy is a more
        therefore involve sampling multiple LNs,   of head and oral tumours can be especially   targeted  and  personalised  staging
        with associated increased patient morbidity.   unpredictable. Lymph nodes targeted would   approach, it significantly reduces morbidity
        It may also risk missing LN metastasis as   have included bilateral mandibular, medial   compared to more extensive LN sampling.
        LNs  considered  less  likely  to  be  draining   retropharyngeal,  parotid  and  prescapular   It also increases the detection of metastatic
        the tumour, based on anatomic location, are   LNs (a total of eight, many of which require   disease  –  in  humans,  30%  of  patients
        unlikely to be sampled with this approach.   ultrasound-guided sampling).   benefit from additional therapies that would
          Sentinel LN mapping involves the    Following SLN mapping via indirect   not have otherwise been offered. For canine
        administration of a contrast agent around   CT lymphography (ICTL), three SLNs   MCT, as in Beetle’s case, the extirpation of
                                                                                metastatic LNs (and even the prophylactic
         CT images following Beetle’s SLN mapping. Iohexol contrast was injected around the scar in four-  removal of regional non-metastatic LNs) can
         quadrants (asterisk), and afferent lymphatic drainage can be visualised (arrows) heading towards
         two of the SLNs (left parotid and mandibular LN).  The drainage towards the third SLN (right   improve outcome, so accurate identification
         mandibular) is not shown in this image.                                of SLNs is crucial.
                                                                                 The Oncology Service is committed to
                                                                                providing the most up-to-date diagnostic
                                                                                and therapeutic options to improve patient
                                                                                quality of life and outcome and is one of few
                                                                                centres to offer SLN mapping via both ICTL
                                                                                and contrast-enhanced ultrasound.




                                                                                       For small animal referrals, please call:
                                                                                     01707 666399
                                                                                       Email:
                                                                                     qmhreception@rvc.ac.uk

        4   Summer 2023
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