equine oncology Flashcards
What is the most common neoplasia of the horse
Sarcoids
Up to 2% prevalence
What is the cause of sarcoids and what cells are neoplastic
Bovine papillomavirus 1 and 2 are involved
= neoplastic proliferation of fibroblasts
What are the 6 types of sarcoids
Occult
Verrucose
Neodular
Fibroblastic
Mixes
Malevolent
What do occult sarcoids look like
Just a hairless raise area; = first early lesions and easy to miss
What do verrucose sarcoids look like
Warty, crusty dry lesions
Start discretely but can spread
What area are nodular sarcoids especially infiltrative
Periocular region
What do fibroblastic sarcoids look like
Ulcerated skin mass, often discrete and simple to treat
What are malevolent sarcoids
Rare form that spreads quickly along lymph vessels and are poorly defines
What are some predilection sites for sarcoids
Anywhere with less hair i.e periocular, axillary, inguinal, sheath
+ sites of previous wounds
what is the correlation between histopath of sarcoids and their clinical appearance; what about prognosis
No correlation
Makes biopsy harder to justify when there is a high sensitivity/specificity of presumptive visual diagnosis
What are the treatment options for sarcoids (in success order)
Radiotherapy is best
Laser surgical resection = good first line treatment for most lesions since more accessible
Electrochemotherapy
Intralesional treatments
Topical treatments; very variable success
What is plesiotherapy
= radiotherapy using strontium90 beta paricles; short penetration so good for small superficial lesions
What is brachytherapy
Radiotherapy using iridium gamma therapy
Has good penetration so can be used for any lesion
= gold standard for periocular lesions
What is teletherapy
Using linear accelerator to create beta or gamma beams
Needs GA so rarely done
What is the gold standard treatment for periocular sarcoids
Iridium brachytherapy
What are some complications that can occur with radiotherapy
White hair formation, alopecia
Can get scar tissue formation
May see transient uveitic with brachytheraphy near eye
Osteoradionecrosis, non-healing wounds, damage to tooth roots rare
How does laser surgical resection
Cut out region with laser and leave open wounds to granulte by second intention
What is the success of laser surgical resection
High; ~80% per lesion
So is a practical, effective and accessible first line treatment for many
Complications of laser surgical resection
Non-healing wound
Recurrence + aggressive transformation
What is electrochemotherapy
= where chemotherapeutic (e/g cisplatin) agents are injected into the lesion and then electrodes are used to enhance the penetration
Can be used in conjunction with other treatments
What are some considerations and complications of electrochemotherapy
Needs a GA for the horse
Health and safety concerns
Can lead to necrosis and wide slough, pain and oedema, non-healing wound
What must we remember when considering intralesional therapy for sarcoids
Need a lesion to inject into
Cannot do on verrucose or occult sarcoids since these are flat; will get very large slough and risk of leakage of drug
i.e for nodular and fibroblastic
What are some agents for intralesional therapy
Cisplatin
Mitomycin C (DNA damaging chemo)
Tigilanol tiglate
Immunocidin
How does Tigalanol tiglate (Stelfonta) work (intralesional therapy)
Causes haemorrhagic necrosis of the tumour
Risk = very large area of sloughing inc down to bone
How does immunocidin work (intralesional therapy for sarcoids)+ risks
Contains mycobacterium wall fraction
Immune modifying
Risks = swellin, pain, abscessation
How does 5-fluorouracil work and which lesions is it good for
DNA damaging chemo cream
Good for verrucose and occult lesions (flat)
2/3 success
Can get sore and cruty, skin scald may happen
What is AW-5 liverpoor cream
Secret formula chemo agent
What complications can occur with AW-5 cream
Wide local slough, severe pain, oedema
What is imiquimod and which sarcoid lesions is it good for
Immune-modifying agent
Good for occult lesions i.e superficial
Treat 3 x per week until lesion goes away
Must clean lesion each time
How does bleomycin work and which sarciods is it good for
DNA damaging chemo cream (but less risky than other chemos if gets into eye etc)
Only for occult lesions
What is tazarotene and what use might it have in dealing with sarcoids
Retinoid cream
Can be used to reduce the crust on verrucose lesions before applying 5-FU crean
Some effect alone
What is the best first line treatment for most sarcoids
laser surgical resection
Where do we typically see skin squamous cell carcinomas
Non-pigmented skin; third eyelid, limbus, cornea
all related to solar exposure
What does a typical SCC look like
Rapidly proliferating cauliflower lesions
But can look much less obvious
What should we suspect a squamous cell carcinoma in a horse
Any unusual ocular or periocular presentation
Corneal and conjunctival infiltrates may be very artypical
Biopsy a good idea
What is the most common squamous cell carcinoma in the horse
3rd eyelid
Are genetics involved in SCCs
Yes one of the syndromes is genetic
What is the cause of genital SCC
Virally-mediated; equine papilloma virus 2
Classic cauliflower lesiosn
What are pale white lesions near a genital SCC
early SCC plaques i.e precancerous change
Where do we see gastric SCCs and what is the prognosis
= rare type of SCC: typically seen at pylorus
OFten diagnosed late and already metastasised so poor prognosis
What do sinus SCCs present like
Primary sinusitis so often just put on antibiotics and get to a late stage before proper diagnosis
Eventually erode through bone and cause facial deformation
How do we treat squamous cell carcinomas
Wide surgical excisino = treatment of chocie
Radiotherapy can be a good adjunctive since SCCs are very sensitive
May do topical/intralesional treatments
What is the prognosis for SCCs like after treatment
about 1/3 of eye lesions recur
10-30% of penile ones do
Can recur years later
What radiotherapy would we use for squamous cell carcinomas
Strontium90 plesiotherapy
What prophylactic drugs do we put a horse on before giving tigilanol tiglate
Place subpalpebral lavage and use prophylactic topical NSAIDs and atropine and systemic NSAIDs
Due to risk of uveitis
How does 5-FU work
structural analogue of thymine so inhibits DNA formatino by blocking thymidylate synthetase
Taken up more by tumour cells
Why might we use piroxicam in equine SCCs
BEcause COX-2 is overexpressed and this is an inhibitor
No clear evidence; could be a good adjunctive
Why should we always stage SCCs
Because many have already metastasised at first presentation (~10%); so should tell owner care will be palliative
Characteristics of melanoma in the horse and predilection sites
Usually benign
Predilection sites = perianal, tail, sheath, parotid salivary glands
Which horses do we see melanomas in
Mostly grey horses; almost all have one in middle to old age
How do melanomas change over horse lifetime
Grow and multiply
Can become necrotic, ulcerated and lead to seconday issues e.g maggots in sheath, rectal impaction
Benign but may eventually metastasise
What are the treatment options for melanoma
Surgical excision is treatment of choice if possible
Laser resection also good
There is oncept melanoma vaccine
How does oncept melanoma vaccine work
Xenogenic human DNA vaccine against tyrosinase
Can stabilise melanoma by preventing further growth or new lesions
But won’t cause regression
How common is lymphoma in horses and what are the forms
Rare - but most common of the haematopoietic neoplasms
Forms = multicentric, alimentary, mediastinal, cutaneous, solitary
How do we treat solitary lymphoma
Wide local excision usually curative
Characteristics of cutaneous lymphoma and treatment
Can wax and wane for years
Prednisolone is a palliative treatment
Chemo has been described
What types of haemangiosarcoma are possible and where do we see disseminated disease
Rare
Cutaneous, locally invasive or disseminated
Disseminated goes to lung, pleura, skeletal muscle, spleen
What are some common clinical complaints with disseminated haemangiosarcoma
Dyspnnoea
Swelling
Epistaxis
Lameness
Can we treat haemagiosarcomas
Cutaneous lesions can be surgically resectable
Locally invasive and disseminated forms mostly untreatable
Characteristics of mast cell tumours in horses
Generally benign
Respond well to surgical excision/intralesional corticosteroids
Where do we tend to find basal cell carcinoma in horses
Ditsal limb and tail
Otherwise look like sarcoids
Treat with wide local excision
What are the different SCC syndromes in the horse
Skin lesions; non-pigmented skin
Genetic
Genitalisa
Gastric
+ others
Which tumours are paraneoplastic syndromes esp common with
Lymphoma
(paraneoplastic fever, thrombocytopaenia, pruritis)
