Large animal cutaneous neoplasia
Surgical debulking is the removal of as much of the tumor as possible; this term is used particularly when the tumor is not totally removed. Tumors can be removed using standing sedation or general anesthesia. Remember to obtain wide margins and to submit a section for histopathology. This is the primary option available for your food animal patients. In general, most tumors will also need another form of treatment. Surgical debulking alone is considered inappropriate for sarcoids; ALWAYS plan to include another form of therapy for sarcoids.
When removing a mass, remember that circles don’t heal well. Most tumors are removed using a fusiform incision (football shaped, pointy at the ends). Check out the lines of tension so that you are closing with them vs against them. If you incise parallel to the lines of tension, the incision will gap the least and the resulting scar will be the smallest. Incisions made at oblique angles to the lines of tension will become curvilinear and incisions made perpendicular to the lines of tension will gape most widely and heal with the largest scars.
Presuturing can be used to stretch the skin in advance of removing the tumor. This procedure relies on the stretch that occurs when skin is kept under tension. Edema develops after 24 hours and interferes with the stretch benefit. Presuturing for 2.5-8h has been useful.
From Auer & Stick:
The direction of suture placement is chosen according to the anticipated direction of primary closure. Wounds of the body and upper limb are generally the most amenable to presuturing. Large, nonabsorbable sutures (No. 1 or No. 2, polypropylene or nylon) are placed through the skin perpendicular and 2 to 6 cm to either side of the lesion. The sutures are then tightened to elevate and fold the skin over the lesion or wound. If presuturing is used in conjunction with tumor excision, the surgeon should be careful to place the sutures distant to the lesion to avoid iatrogenic seeding of tumor cells into healthy tissue.
Cryosurgery damages the tumor cells through the creation and melting of ice crystals. To get the best ice crystals, freeze the tissue quickly and let it thaw slowly. This is repeated at least once. The second and third time, the precooled tissues freeze faster, creating a better kill of tumor cells. Don’t try to heat the tissues to speed the thaw. Let them return to normal temperature on their own. For people, they keep freezing until the tissue stays cold.
Liquid nitrogen used for cryosurgery does need to be carefully stored and transported. It is delivered to the tissue through spray guns or super chilled probes. It is important to protect surrounding tissues when using the spray guns. Vaseline and Styrofoam cups (easily torn to the right size) are commonly used. Many tumors will respond to cryotherapy and it can be used after debulking to treat the wound margins. You may need to wait until bleeding subsides in order to obtain a good ice ball as the blood is warm and keeps heating the area. While thermocouples are nice to have, most clinicians gauge the amount of freeze by the size of the ice ball. The central 75% of the ice ball will be sufficiently cold to kill tumor cells.
After cryosurgery, the tissue will swell over the next 48 hours and will necrose in 14-21 days. Hair may turn white or may not regrow. Tissue will scar: “do not freeze where scars may squeeze”. Eg freezing a SCC on the urethra might not be a good option. Cartilage is very sensitive to freezing and may be damaged or misshapen if it becomes too cold (eg be very careful freezing tumors on ears). Repeated treatment is often necessary.
The investment cost and cost of the liquid nitrogen is relatively small making it one of the more affordable options for practices.
Cisplatin beads and chemotherapy injections
Cisplatin (a chemotherapeutic agent designed to kill tumors) is often effective against tumor cells if it can be kept in the affected region. In horses (and non-food animals), the bead form has been the easiest and seems to be the most efficient. Commercially produced beads are inserted into the tumor through small stab incisions to cover as much of the tumor as possible. The beads release cisplatin over time and generally need to be replaced every two weeks. Cisplatin injections are cheaper but require mixing with oils to prolong their activity and can be quite messy and therefore dangerous for the user. Users should take appropriate precautions with both and avoid contact with the beads or solution. 5FU is also available in an injectable form.
Topical agents can be dispensed and applied by the owner. Many of these result in irritation to the horse so cleaning and reapplication may require veterinary assistance. The most common compounds are imiquimod (useful for sarcoids and probably SCC) and 5-fluorouracil (used for penile and vulvar SCC). Xxterra is also being used for tumors but is not well studied. Watch for more options to appear; always check the literature vs the website or sales rep!
Most other therapies will only be available at referral centers due to equipment cost or health/safety restrictions. Laser debulking is frequently used for tumors that come into the UMN. The CO2 laser removes cells layer by layer, making it one of the safest options to use in tricky areas. It also destroys the nerves to the tissue, giving the horse some pain relief as well.
Laser treatment is often useful to start treatment and is done at a referral center. After debulking, field treatments can be used to continue the therapy and/or keep the tumor at bay.
Autogenous vaccines have been tried (and given up on) for melanomas. They are currently resurfacing for sarcoids. BCG has been used to stimulate an immune response for ocular tumors but does carry a risk of death; imiquimod is safe to use around the eye and no deaths have been reported. Radiation therapy is possible but is often cost prohibitive for horses. You can always call us for the latest info on a tumor or treatment option!
Field management is possible but is often more successful after initial treatment at a referral center. Multimodal therapy is recommended.
Field therapies include:
- Surgical removal
- Topical or local agents – imiquimod, 5 fluorouracil, cisplatin beads