Histiocytic sarcoma
or osteosarcoma...
That is the question

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

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

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

Radiographs sent
Ulna involvement - unusual

Radiographs sent
No pulmonary metastatic nodules were seen on chest radiographs

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

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

CT thorax (lung window)

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

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

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…

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

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

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

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!

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

Back to Jerri…
Histiocytic sarcoma?
Osteosarcoma?

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.

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

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

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)

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

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

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