This document discusses the case of a 10-year-old female Rottweiler named Jerri who presented with sudden lameness in her left forelimb. Radiographs and CT scans revealed an aggressive soft tissue lesion invading and destroying the proximal left ulna, likely a neoplasm. Fine needle aspirates of the swelling showed round cells consistent with either osteosarcoma or histiocytic sarcoma. Given the patient's breed and unusual location of the lesion, histiocytic sarcoma could not be ruled out. Treatment options of amputation, radiation therapy, chemotherapy or palliative care were discussed. The owner elected to pursue radiation therapy with the goal of palliation.

1. Histiocytic sarcoma
or osteosarcoma...
That is the question

2. Jerri McIntosh
• 10yo FN Rottweiler
• Referred to the SAH Oncology
service for “treatment/mgmt of
an osteosarcoma”
• A month ago: suddenly yelped &
became non-weight bearing
lame whilst running about
• At local vet’s: radiographs (& referral) + tramadol +
advised strict rest

3. History
• EDDU all fine
• had adhered to rest instructions - only let out to
garden
• left forelimb lameness improved but not entirely
• generally happy at home though the tramadol
made her quite sedated
• known right forelimb osteoarthritis of 3 years
duration
• has meloxicam for that

4. Clinical exam
• bright & alert
• visibly lame on left fore but mostly weight-bearing
• feeling the limb, noted a firm swelling of muscle-&-
soft-tissue consistency
• local draining lymph nodes (prescaps, axillary) not
palpably enlarged or firm
• NAD on chest auscultation and abdominal
palpation

5. Radiographs sent
Ulna involvement - unusual

6. Radiographs sent
No pulmonary metastatic nodules were seen on chest radiographs

7. Our plan of action
o routine bloodwork (haem & biochem)
o CT scan of elbows (both)
o CT scan of thorax
o Abdominal ultrasound scan
o FNA of the swelling
• in-house + sent up to the clinical pathology unit
• multiple slides to account for variation within the
lesion
The obligatory metcheck

8. Test results / findings
• Routine blood work
o Haematology unremarkable.
o Biochemistry mild elevation of AST but no increase in ALP (often seen with
OSAs)
• Abdominal ultrasound scan
NAD

9. CT thorax (lung window)

12. Diagnostic imaging dx:
Large aggressive soft tissue lesion with invasion and destruction of
proximal left ulna - likely neoplastic.
CT forelimbs (bone & soft tissue windows)

13. Right elbow also showed aggressive lytic change,
Centred especially on right medial humeral condyle.
CT forelimbs (bone & soft tissue windows)

14. FNAs & cytology
• High numbers of roundish/polygonal cells, many
with multiple nuclei
• Anisocytosis and anisokaryosis
• Some spindle cells, many of which were binucleate
and had multiple nucleoli
• Monomorphic population of mesenchymal cells
exfoliating individually and in aggregates…
• Associated with amorphous, pink extracellular matrix
(osteoid or collagen)…
• Cells ranging in shape from oval to polygonal to
spindle…
• Nucleus round to oval, often eccentrically located…

15. Types of tumours that can
affect bone in dogs
• Osteosarcoma
• Chondrosarcoma
• Fibrosarcoma
• Haemangiosarcoma
• Rhabdomyosarcoma
• Histiocytic sarcoma
Metastatic tumors that
may present clinically as
bone tumors:
• Carcinomas
• Plasma cell myeloma

16. Osteosarcomas
• 85-90% of primary bone tumours
• Appendicular skeleton > axial skeleton
• large and giant breeds >> small breeds
• Predilection sites:
away from
the elbow,
towards the
knee

17. Osteosarcomas
• Transformed malignant cell is the osteoblast
• Neoplastic cells often round/ovoid
Cowell & Tyler – cells from a canine osteosarcoma
and not

18. Histiocytic sarcomas
• transformed malignant cells
are interstitial dendritic
antigen-presenting cells
(APCs)
• Uncommon in dog
population as a whole
• But tremendously common in
certain breeds Cowell & Tyler – aspirate from a histiocytic sarcoma
Round, discrete cells!

19. Histiocytic sarcomas
• 2 forms
o Localised
• deep limb musculature and periarticular
• Highly malignant and metastatic
o Disseminated
• both localised and disseminated forms carry quite a
guarded prognosis

20. Back to Jerri…
Histiocytic sarcoma?
Osteosarcoma?

21. Jerri’s FNA slides -­‐‑
discussion
• Cytology can be rewarding but also confusing,
especially to the unpractised eye
• Special cytochemical stains available
o BCIP/NBT solution stains ALP in osteoblasts
o ANBE stains intracellular esterase enzymes that are present in cells of dendritic/
monocytic origin
• Variation amongst different sites of the lesion sampled
Provisional diagnosis:
Lytic bone tumour of left ulna.
Sarcoma.

22. Treatment options
• Amputation + follow-up with chemo = first-line
• Radiotherapy
• More analgesics
o e.g. tramadol , fentanyl patches
• Bisphosphonates
o help reduce bone lysis and pain
Palliative intent

23. Considerations
• Tried simulating a left forelimb amputation by
bandaging it up
• The worrying CT scan findings
o Pulmonary metastases – prognosis slightly poorer (though early stage
metastatic disease as not detected on radiography yet)
o Compromised right elbow – arthritic change + possible neoplasm as well

24. Recommendations and
owner’s decision
• Radiotherapy
• +/- chemotherapy to follow
o explained would be much less effective as, even though irradiated,
whole mass still there
• +/- bisphosphonates and additional analgesic
medication
Jerri went home on metacam SID and she’s scheduled
to come in week commencing 15 sept for a 5d course
of radiotherapy (palliative intent)

25. Updates
• Owner has called on 2 occasions
o Worried about Jerri’s lameness
o Wondering if can XRT both forelimbs – going to give it a go
• Jo also thinking of doing a repeat FNA (just for
interest’s sake)
o Definitive diagnosis more important only if owners decide to follow on with
chemo
o As would influence choice of agent
• OSA à carboplatin
• Histiocytic sarcoma à lomustine

26. Key points
• Although osteosarcomas are the most
commonly occurring primary bone tumours, if
lesion is not in usual predilection site, then also
consider:
o Histiocytic sarcomas – particularly in Bernese Mountain
Dogs, Flat coated retrievers, Rottweilers & Golden
Retrievers
o Secondary mets – esp from mammary/prostatic
carcinomas and multiple myeloma
• Always take radiographs of (or CT scan)
opposite limb as well !
o Very helpful for comparison + evaluating patient
suitability for surgery

27. Julie, who initially saw Jerri
Gawain Hammond, for imaging interpretation advice
Jo Morris, for going over the case with me
Everyone here, for listening J