Equine Skin Tumors Flashcards
Take home messages for skin tumors in horses
- No one shot cure for cancer
- Pick your battles - not every tumor needs to be treated
- SKin tumors in horses are different than small animal and human
- Don’t make a situation worse (wide margins may not be indicated in areas with limited skin; widen margins with adjunct therapy)
How are skin tumors in horses different than in people?
- Very slow to metastasize
- Unusual for a horse to die of cancer
If you are going to biopsy a tumor in a horse, what should you be ready to do?
- Be ready to treat
- Often do excisional biopsies in horses
Keys to success with skin tumors
- Be more aggressive than the tumor
- Be more stubborn/persistent than the tumor
- Make sure owners are committed to the fight before you start
- Have multiple tools in your toolbox
What % of skin tumors of all equine neoplasms?
- 50%
What is the most common skin tumor?
- Sarcoid
When are most sarcoids diagnosed?
- at necropsy
Are most sarcoids impactful on the horse?
- No, they are often incidental findings
Cell origin for sarcoids
- Fibroblastic tumors
- If it’s a fibrosarcoma diagnosis or nerve sheath tumor, he will treat it like a sarcoid
Invasiveness and metastatic potential of sarcoids
- Locally invasive
- Non -metastatic
- Often benign and considered incidental finding
What’s the biggest problem with sarcoids?
- May disrupt eyelid functio nor indirectly damage the eye
- May be in locations on the body that inhibit normal use or function
Age of horses with sarcoids
- Horses 3-6 years of age
- 70% less than 4 years
- Diagnosed in yearlings**
- Risk drops off after 15 years
Breeds of horses with sarcoids
- Quarter Horses, APpaloosas, Arabians
Heritability of sarcoids
- Increased incidence in certain families, and a genetic link with specific major histocompatibility complex genes has been demonstrated
Bovine papillomavirus and sarcoids
- No intact viral particles have been demonstrated in sarcoids so far, DNA, RNA, and proteins of the virus can be found
- Detected in both normal skin and tumors
- Detected in peripheral blood mononuclear cells of sarcoid bearing horses
- Aggressive tumors have a higher viral load
Transmission of bovine papillomavirus to horses
- Unknown
- Direct or indirect?
- In donkeys it is known that animals having close contact with affected animals are at a higher risk for development of sarcoids
Flies and BPV and sarcoids
- Flies or other insects may play an important role as a mechanical vector in BPV infection of the horse
- presence of BPV-1 and 2 in Musca autumnalis face flies infestning sarcoid affected horses
What are the 6 different types of sarcoid?
- Occult
- Verrucose
- Nodular
- Fibroblastic
- Mixed
- Malevolent
What is the most benign type of sarcoid?
- Occult sarcoid
What can happen if you biopsy a sarcoid?
- It can come back more aggressive
Occult sarcoid locations
- Around mouth, eyes, neck or other hairless areas
Appearance of occult sarcoids
- Areas with mild hyperkeratosis, slightly thickened skin +/- color change
- Can occasionally be mistaken for ringworm or even rub marks from tack
Occult sarcoids - can they ever change?
- Yes, they may convert
- They may also be worsened by biopsy
What is the most common type of sarcoid?
- Verrucose or warty sarcoid
Location for verrucose or warty sarcoid?
- Face, body, and groin/sheath areas
Appearance of verrucose or warty sarcoid?
- Rough, hyperkertatotic appearance and scaling
- Sessile (flatbased) or pedunculated
Growth of verrucose or warty sarcoid
- Often slow growing and not very aggressive until injured or insulted
- Change to fibroblastic sarcoid
WHere do nodular sarcoids occur?
- Groin, sheath, or eyelid areas
Appearance of nodular sarcoid
- Firm, well-defined subcutaneous, spherical nodules
- Nodules usually lie under apparently normal skin and may be freely movable
- May have dermal and deep attachments
Treatment for nodular sarcoids
- He likes to make an incision, take them out, and then close the incision over the top
Fibroblastic sarcoid - where do they occur?
- Groin, eyelid, lower limbs and wounds
- Sites of other types of sarcoid subjected to trauma or insult
Appearance of fibroblastic sarcoid
- Characteristic fleshy appearance
- Pedunuclated and extensive
Appearance of fibroblastic sarcoid
- Looks like proud flesh
- sessile tumors with ulceration
How can you differentiate exuberant granulation tissue (proud flesh) from sarcoids?-
Anywhere above the hock or knees you should think sarcoids
Mixed sarcoids
- Progressive/transient state between the occult/verrucous types and fibroblastic/nodular types
Where do malevolent sarcoids appear?
- Jaw, face, elbow, and medial thigh areas
- History of repeated trauma to other types of sarcoid (e.g. surgical
Aggressiveness and metastasis of malevolent sarcoids
- VERY aggressive, spread rapidly
- Infiltrate in lymphatic vessels resulting in multiple in multiple nodular or fibroblastic masses along these vessels
- Local lymph nodes might also be involved
What should you do if you have a non-healing wound anywhere not responding to treatment?
- Biopsy the skin margins
- Could be SCC or sarcoids
Management of Tumors
- Surgical excision
- Laser ablation
- Cryotherapy
- Hyperthermia
- Chemotherapy
- Topical cytotoxic drugs
- Electrochemotherapy
- Immunologic methods
- He usually likes to see every 2-3 weeks for it to start healing but not too much
- He gets rid of anything abnormal
Type of margins for tumors
- Reasonable but not excessive
- If the skin moves above it, he leaves it in
What can be a side effect of cryotherapy?
- Turns the skin white
What is the drug of choice for electrochemotherapy/chemotherapy?
- Cisplatin
- Can enhance its uptake with electrochemotherapy
What can happen if you have multiple sarcoids related to a virus and you take care of one?
- The rest can fall off
- In 10% of the cases
What is the second most common tumor in horses?
- Squamous cell carcinoma
- 20-25% of equine skin tumors
- Most common tumor of the equine eye and ocular adnexa as well as external genitalia
Age of horses with squamous cell carcinoma
- 11-19 years
Metastasis with SCC
- As high as 20%
- 10% of horses with ocular tumors have a second mass at a different site
- SLow but steady
Where on the body do SCCs tend to occur (external forms) ?
- White, light colored skin
- Eye, conjunctiva, ocular adnexal structures
- Penis, vulva, eyes, lips
Where in the body do SCCs tend to occur (internal forms)?
- Stomach, esophagus
- nasal passages, pharynx, larynx
- Perianal tissue
- Lungs
Risk factors for SCC
- Sun damaged skin (high altitude)
- Light pigmented skin (white, grey, cremello)
- Breed (Draft, Appaloosa, Paint)
- Persistent phimosis, smegma, trauma to the external genitalia
- maybe papilloma virus?
What to do for treatment of TEL SCC?
- Surgical excision of the TEL
- Follow up and remove it all
- Subpalpebral lavage and treat with mitomycin C for one course of treatment
Penile SCC treatment options
- He often starts off with treatment of 5-FU
- Drug will stick around long enough in the penis
- May be more aggressive in young horses
- Surgical amputation of the penis can be treatment of choice
- You can amputate or remove the whole penis and PU
- Chemo and laser therapy don’t work very well
- Radiation therapy if he could, but it would be like 15-18 anesthesias
Melanocytic tumor cell origin
- Melanocytes, dendritic cells of neuroectodermal origin, or melanoblasts
% of skin tumors for melanocytic tumors
- 3.8-15% of all skin tumors
Which horses get melanocytic tumors?
- Grey horses
- Other horses too of any age or color, but then they tend to be worse prognosis
- Arabians, Percherons, Thoroughbreds
% of older grey horses that develop melanocytic tumors? % of those that are NOT malignant?
- 80%
- 2/3 are not malignant
Location of melanocytic tumors?
- Undersurface of tail near the base
- Perineal and perianal regions
- Genitalia
- Mammary gland
- Base of the pinna
- Commissures of the lips
- SKin around the eye
- Parotid salivary gland
Treatment for melanocytic tumors - can you remove them?
- He’s removed a lot
- They don’t come back
- Might grow near that area
- If there in an area where they might eventually become a problem, do an excisional biopsy when they’re little
- Don’t have to do wide margins, but it can help
Melanocytic nevus appearance and description
- Benign tumors that appear as a single, discrete solitary mass and affects younger horses of all coat colors
WHo gets melanocytic nevus?
- Younger horses of all coat colors
- Most horses were 6 years old or younger
Location of melanocytic nevus tumors?
- Atypical areas such as the umbilicus, forelimb, rump, shoulder, thigh, neck, and cannon bone
Treatment for melanocytic nevus?
- Surgical removal usually curative
Dermal melanoma description
- Discrete, solitary masses (1-2 tumors) in older gray horses
Mean age with dermal melanoma
- 13 years
Dermal melanoma behavior
- Most tumors are benign
Location of dermal melanomas
- “Typical sites”?
- Commissure?
Treatment of dermal melanomas
- Surgical excision of noninvasive tumors usually curative
Dermal melanomatosis who gets?
- Horses 15 years or older
Metastatic potential of dermal melanomatosis?
- Internal metastasis is likely
Treatment and prognosis for dermal melanomatosis?
- Surgical excision is often curative for the masses that are removed, but the remaining masses continue to grow, and new tumors develop
Treatment discussion for a tumor around the tail head?
- Shell it out and leave it to heal by second intention
- Palliative treatment
- OFten heal well
- Keep it clean with a fly spray
- Eventually granulate in well and do well eventually
Who gets anaplastic malignant melanomas?
- Older horses (usually >20 years) of any hair color
Histologic features of anaplastic malignant melanomas?
- Variable pigmentation, extremely pleomorphic epithelioid cells, single cell invasion of the epithelium, and numerous mitotic figures
Metastatic potential of anaplastic malignant melanomas
- Uncommon, but metastasize quickly
Risk of disease for anaplastic malignant melanomas between gray and non-gray horses
- The same
Treatment for anaplastic malignant melanomas
- Not a good treatment
- Autologous vaccines not usually successful
- Oncept (human tyrosine kinase might be helpful in a non-gray horse)
mast cell tumors - how common?
- Uncommon
Mast cell tumor sex, breed, and age predilection?
- Sex: males 5x more likely than females
- Arabian horses predisposed
- No age predilection
Treatment of mast cell tumor
- Surgery or radiation
What are the two types of mast cell tumors in horses, and which is most common in horses?
- Two types are hyperplastic type and neoplastic type
- Most equine mast cell tumors are hyperplastic
CLinical presentation of mast cell tumors
- Most common is a single cutaneous nodule, often located on the head
- Surface of the nodules may be normal, hairless, or ulcerated
- Diffuse swelling on a lower extremity, usually below the carpus or hock
- Swelling is firm, and the overlying skin is normal in appearance
Radiographs of MCT on lower extremity
- Multifocal areas of soft tissue mineralization
Diagnosis of MCT
- Biopsy
