Do Lawn Treatment Chemicals Cause Cancer in Pets? A growing body of research says yes!

Cancer is one of the most important health issues affecting household pets. Causes of cancer are many and varied, including genetic predispositions, certain viruses, and exposure to environmental toxins. Many studies in both humans and animals have focused on the increased risk of cancer from chronic use of chemicals such as pesticides and herbicides around the household.  Since dogs and cats have significant exposure to grassy areas of properties, lawn chemicals in particular have been studied for the potential of causing health problems.

Several studies have now shown an association between the frequently used chemicals on household lawns and cancer in dogs.(1-4) Dogs chronically exposed to the herbicides and pesticides in lawn sprays and granules are more likely to get cancers such as lymphoma and transitional cell carcinoma of the urinary bladder. An initial study published in the Journal of the National Cancer Institute in 1991 found that homeowners that frequently used the herbicide 2,4- dichlorophenoxyacetic acid on their lawn had a statistically significant higher rate of lymphosarcoma in their dogs.(1) Lymphosarcoma, also called malignant lymphoma, is a common cancer affecting lymph nodes and other organs and lymphatic tissues. This study was heavily criticized by other investigators who questioned the validity of the results. However, a more recent study published in 2012 analyzed 263 dogs with lymphosarcoma and found a 70% increase in risk of the cancer in households with professionally applied pesticides on the lawns.(2)

Two studies at Purdue University College of Veterinary Medicine have also found disturbing results of dogs exposed to herbicides, particularly the phenoxy herbicides such as the previously mentioned 2,4- dichlorophenoxyacetic acid, also called 2,4-D.(3,4) 

Herbicides were found in the urine of 76% of dogs from households that used them on their lawn.(4) The herbicides were also found in the urine of some dogs from households where the herbicide was not used, indicating they were exposed to them in areas other than their own property. 

The additional study from Purdue found that Scottish Terriers living in households that used herbicides alone or herbicides and pesticides on their lawns were markedly more prone to transitional cell carcinoma of the urinary bladder.(3) This study, along with the former one looking at the chemicals being present in the urine, are convincing evidence that the herbicide exposure is directly related to bladder cancer in this breed. Other breeds could be examined in the future to further define the risks of exposure. 

More research is needed to elaborate the dangers of lawn chemicals to our pets, but these well designed and executed studies make it clear that the commonly used pesticides and herbicides being indiscriminately sprayed and broadcast on our lawns are causing cancer in dogs. Many provinces in Canada have completely banned what they call “cosmetic” use of herbicides and pesticides because of the potential health problems. Cosmetic is a good term because the cancer causing chemicals are being used merely to improve the appearance of our lawns. Maybe we should be more tolerant of less than perfect grass if it decreases the adverse health effects on our pets. 

Although additional studies will help to better define the problem, we now have sufficient evidence to raise serious concerns about the dangers of herbicides and pesticides used on lawns. Homeowners should be educated about these issues so that they can take appropriate action to protect their pets from harm. Professional lawn care companies also need to carefully consider their protocols and make necessary changes to stop contaminating the environment with chemicals that are now proven to be carcinogenic to pets. 

References

1. Hayes HM1, Tarone RE, Cantor KP, Jessen CR, McCurnin DM, Richardson RC. Case-control study of canine malignant lymphoma: positive association with dog owner's use of 2,4- dichlorophenoxyacetic acid herbicides. J Natl Cancer Inst. 1991 Sep 4;83(17):1226-31. 

2. Biki B. Takashima-Uebelhoer, Lisa G. Barber, Sofija E. Zagarins, Elizabeth Procter- 
Gray, Audra L. Gollenberg, Antony S. Moore, and Elizabeth R. Bertone-Johnson. Household Chemical Exposures and the Risk of Canine Malignant Lymphoma, a Model for Human Non-Hodgkin’s Lymphoma. Environ Res. 2012 January ; 112: 171–176. 

3. Glickman LT1, Raghavan M, Knapp DW, Bonney PL, Dawson MHJ. Herbicide exposure and the risk of transitional cell carcinoma of the urinary bladder in Scottish Terriers. J Am Vet Med Assoc. 2004 Apr 15;224(8):1290-7. 

4. Knapp DW1, Peer WA, Conteh A, Diggs AR, Cooper BR, Glickman NW, Bonney PL, Stewart JC, Glickman LT, Murphy AS. Detection of herbicides in the urine of pet dogs following home lawn chemical application. Sci Total Environ. 2013 Jul 1;456-457:34-41. 

Should We Spay Dogs When Removing Mammary Tumors? This study answers that question.

V.M. Kristiansen, A. Nødtvedt, A.M. Breen, et. al. Effect of ovariohysterectomy at the time of tumor removal in dogs with benign mammary tumors and hyperplastic lesions: A randomized controlled clinical trial 
J Vet Intern Med 2013;27:935–942 

Summary

The authors of this study sought to answer the following question: is there a clinical benefit to performing ovariohysterectomy (OHE) at the time of benign mammary tumor removal in dogs.  Their hypothesis was that removal of ovarian hormones by OHE would decrease the development of new benign mammary tumors and thus would have important clinical ramifications. In a randomized, controlled clinical trial, dogs having surgery to remove benign mammary tumors were placed in one of 2 groups: those also having OHE performed at the time of tumor removal (n=42), and those not having OHE performed (n=42). All tumors were analyzed by histopathology. The dogs were followed for at least 80 months and long term follow-up information obtained either by phone calls to owners or by recheck examinations by veterinarians. 

New benign mammary tumors developed in 64% of in tact dogs compared to 36% of dogs having OHE. This was statistically significant and showed the clinical benefit of concomitant OHE with benign mammary tumor removal. Nine of the intact dogs also went on to develop disorders of the ovaries or uterus, such as pyometra. There was no difference in survival data between the 2 groups. 

Commentary

For years surgeons have recommended OHE in combination with removal of mammary tumors, not because of any proven benefit related to the mammary neoplasia, but to prevent other disorders such as pyometra. This study provides evidence of the benefit of performing OHE in combination with mammary tumor removal. The authors make the case that since dogs that develop benign mammary tumors are also at increased risk of developing malignant mammary tumors, prevention of future malignant tumors may also be a positive factor of OHE.

The lack of difference in survival between the two groups may be misleading since some of the dogs were euthanized. The many and varied issues surrounding the owner’s decision to euthanize make the survival data, in the author’s words, a “soft and biased endpoint in the study.” In contrast, the different rates of tumor recurrence between the 2 groups is objective data in which statistical significance was found.

Conclusions

This prospective randomized study provides objective evidence of the benefit of OHE in dogs being surgically treated for mammary tumors. Clinicians can recommend OHE at the time of mammary tumor removal as evidence based medicine approach to treatment, not just in the prevention of reproductive disorders such as pyometra and ovarian tumors, but in prevention of benign mammary tumors.

Canine Lung Lobectomy Video

Introduction
This is a brief description and video of lung lobectomy in a 14 year old male neutered West Highlight White Terrier named Chester.(Fig. 1) Chester presented for coughing for several weeks, and on plain film thoracic radiographs a mass was seen in the right middle lung lobe. (Fig. 2)

Fig. 1: Chester, a 14 yr old male neutered Westie diagnosed with a primary lung lobe tumor

Fig. 2a: Lateral thoracic radiograph of Chester showing a mass in the right middle lung lobe. (arrows)

Fig. 2b: Ventrodorsal thoracic radiograph of Chester showing the mass in the right middle lung lobe. (arrows)

Surgery
After inducing general anesthesia and placing the dog on a ventilator, a routine right 5th intercostal space thoracotomy was performed. A mass was found on the dorsal aspect of the right middle lung lobe. (Fig. 3)

Fig. 3: Right lateral thoracotomy exposing a neoplasm of the right middle lung lobe (black arrow) in Chester.
Dorsal is to the bottom of the photo.

A lobectomy of the affected lung lobe was performed using the TA 30 (V3) Surgical stapling device. (Fig. 4 and video)

Fig. 4: TA Surgical Stapling device.
(Blue cartridge is shown, white cartridge (V3) was used in the case
described here. (Medtronic.com)

A thoracic drain tube was placed and the thoracotomy closed routinely.

Postoperative Care
The dog recovered well postoperatively and was given supportive care including intravenous fluids, analgesics, and monitoring of vital signs. Minimal amounts of air and fluid were recovered from the drain tube overnight. The drain tube was removed the following day and the dog discharged from the hospital. One week postoperatively the owner reports that Chester continues to do well at home. 

Histopathology of the mass revealed an adenosquamous carcinoma of the lung. Resection was felt to be complete with clean margins. Chester is currently receiving chemotherapy under the direction of our internist, Dr. Joanna Fry and Jessica Herzig, RVT. More updates to come!

Surgical Removal of Giant Lipomas in Dogs

Lipomas are benign tumors of adipose tissue that are common in dogs. Most lipomas are small, well circumscribed, movable, and not painful. They most commonly occur in the subcutaneous space but in rare cases can form in a body cavity such as the abdomen (Fig. 1a-c), or between large muscles such as the semimembranosis and semitendonosis (1).

Fig. 1a: Lateral abdominal radiograph in a dog with an abdominal lipoma.
Note large fat density mass in the mid to caudal abdomen.

Fig. 1b: Ventrodorsal radiograph of same dog as Fig. 1a.

Fig. 1c: Operative photograph of an abdominal lipoma in same dog as the above radiographs.

Lipomas that are large and grow between fascial planes are called infiltrative lipomas. (2,3)

Simple (not infiltrative) lipomas that are small, quiescent, and not causing pain or dysfunction are usually not treated. However, in some cases because of the sheer size and location of the lipoma, surgical resection is recommended. For example, a very large lipoma of the axilla like in the dog illustrated in this article may cause serious functional problems with the front limb.(Fig.2) 

Fig. 2: Preoperative appearance of a very large lipoma of the right axilla in this Labrador retriever

Surgical resection can be performed to allow better use of the leg and relief of discomfort. Even giant lipomas, if not infiltrative, can frequently be surgically removed. However, attention to anatomic detail and meticulous surgical technique are critical to avoid complications.

Diagnosis
Lipomas are suspected in any subcutaneous mass that is soft on palpation, movable, and well circumscribed. Fine needle aspirate samples appear grossly as oil droplets on a slide and reveal few cells microscopically. Radiographs (Fig. 1a,b) or CT scan of the mass may be indicated for very large or infiltrative lipomas that could be near or surrounding vital structures or in a body cavity.(4) 

Preoperative Considerations
Since many patients with lipomas are geriatric, appropriate preoperative evaluation would include a thorough history and physical examination, laboratory tests (CBC and serum chemistry profile) and thoracic radiographs if cardiopulmonary issues are suspected. 

Surgical Technique
After induction of general anesthesia, clip and aseptically prepare a wide field over the lipoma. Make an incision that spans the length of the lipoma. 

Fig. 3: Initial incision in the lipoma on same dog as in Fig. 2.

Using blunt and sharp dissection, define the borders of the mass and separate it from surrounding tissues. Finger dissection is usually effective in defining tissue planes and extracting the mass. When dissecting into deep tissue planes, use retractors to improve exposure and identify important structures such as large vessels and nerves. 

Fig. 4: Dissection of the lipoma in same dog as Fig. 2. The axilla artery and vein
and elements of the brachial plexus are seen at the base of the mass. 

Encapsulated lipomas will usually “peel out” well, but after removal inspect all surrounding tissues for residual lobules of lipoma. 

Fig. 5: Completed resection of the massive lipoma from the axillary space in dog from Fig. 2.

Prior to wound closure, inspect the surgical field for hemorrhage. Since removal of lipomas results in large areas of empty space in the tissues, place a closed suction drain to prevent fluid accumulation and seroma. (See Veterinary Key Points blog on the Jackson-Pratt drain.) 

Fig. 6: A closed suction drain has been placed in the Labrador in Fig. 2
and the incision closed routinely.

Close the wound routinely and place a light bandage on the animal to protect the drain tubing and reservoir. Leave the drain in place until drainage has reduced to trivial amounts. 

In the following video see dissection of a massive lipoma from the lateral cervical region of a dog. Removal of the mass exposed the trachea, carotid artery, and vagosympathetic trunk. 

Prognosis
Simple lipomas, even large ones, have a good prognosis since they are benign and slow growing. Postoperative recurrence is rare, but careful monitoring for development of new lipomas in other parts of the body is advised. Liposuction removal of lipomas was reportedly successful in 1 study but complications were common and recurrence of lipoma was high (28%) (5)

Infiltrative lipomas have a more guarded prognosis because they can be difficult to completely excise and recurrence is more common than with simple lipomas. Depending on the clinical study, one-third to one-half of dogs with infiltrative lipoma will develop recurrence after surgical removal. (2,3) Carefully monitor the surgical area for evidence of regrowth that can occur months or years postoperatively.

References
1. Thomson MJ, Withrow SJ, Dernell WS, Powers BE Intermuscular lipomas of the thigh region in dogs: 11 cases. J Am Anim Hosp Assoc. 1999 Mar-Apr;35(2):165-7.
2. McChesney AE, Stephens LC, Lebel J, Snyder S, Ferguson HR. Infiltrative lipoma in dogs.Vet Pathol. 1980 May;17(3):316-22
3.Bergman PJ1, Withrow SJ, Straw RC, Powers BE. Infiltrative lipoma in dogs: 16 cases (1981-1992) J Am Vet Med Assoc. 1994 Jul 15;205(2):322-4.
4. McEntee MC1, Thrall DE. Computed tomographic imaging of infiltrative lipoma in 22 dogs.Vet Radiol Ultrasound. 2001 May-Jun;42(3):221-5
5. Hunt GB1, Wong J, Kuan S. Liposuction for removal of lipomas in 20 dogs. J Small Anim Pract. 2011 Aug;52(8):419-25. 

Complete Surgical Excision of Mast Cell Tumor in Dogs and Cats

A wide variety of skin tumors occur in dogs and cats, both benign and malignant.  An important principle of surgical management of these tumors is to establish a diagnosis before the operation.  Fine needle aspiration (FNA) is a practical and reasonably accurate method to biopsy skin masses, and the results allow clinicians to plan appropriate treatments.  For example, benign skin tumors such as epidermal inclusion cysts require only a marginal excision and routine skin closure.  Malignant skin tumors, such as mast cell tumor (MCT), require extensive tissue resection (e.g. removal of 2-3 cm of normal tissue with the mass) followed by more complicated reconstruction in some cases.  An adequate deep margin of normal tissue should be removed with the tumor as well as medial and lateral margins. Excise a section of the tissue layer below the tumor to achieve a complete resection. If the tumor is located in the subcutaneous space remove the muscle or deep fascia below the tumor.

Preoperative Considerations

As is true for any animal with neoplasia, tumor staging is done prior to surgery to establish the extent of disease. Appropriate imaging, such as thoracic radiographs and abdominal ultrasound, is used to examine for metastasis or other unrelated problems. Also carefully examine regional lymph nodes and if enlarged perform FNA. With MCT, administer preoperative antihistamines such as diphenhdyramine to reduce the inflammation associated with histamine release by the tumor. The drug can be given either orally for 1 or more days preoperatively, or parenterally just before surgery. Avoid excessive manipulation of the tumor before surgery to prevent degranulation of mast cells and release of histamine.

Be sure to warn owners about potential complications of surgical removal of MCT. Even with antihistamine pre-treatment wound complications such as excessive inflammation, seroma, and dehiscence are possible.

Surgical Technique

After placing the dog or cat under general anesthesia, perform a wide aseptic preparation of the surgical site. (Fig 1) 

Fig. 1: Cutaneous mast cell tumor (circle) over the dorsal thoracic area in a spaniel.
(note Figs 3-7 are the same dog as in this picture)

Use a sterile ruler and marking pen to delineate the mass (Fig 2), then draw a circle around the tumor that is 2-3 cm from the edge of the mass.(Fig 3)

Fig. 2: Sterile surgical marking pen and ruler to map surgical margins around skin tumors.

Fig. 3: MCT (inner circle and X) delineated by an outer circle of 2cm margins of normal skin

Draw lines that taper the incision on each end to make the incision an ellipse and thus avoid having “dog ears” of skin on the ends.(Fig. 3) Be sure that the long axis of the resultant incision is parallel to the tension lines in that area of the body.

Make the incisions on the proposed lines and continue the dissection into the deep tissues. Avoid dissecting toward the tumor; as you proceed deeper in the tissues continue to honor the 2 or 3 cm margin originally mapped on the skin. Once the desired layer of deep margin has been reached, incise the fascia or muscle, lift the tumor and associated tissue (en bloc), and dissect the block of tissue completely free.(Fig. 4)

Fig. 4: Intraoperative picture with skin mass and underlying tissue
being removed from right to left. Note underlying muscle being removed with the mass.

Wide excision of skin or subcutaneous masses frequently leaves large skin defects that can be difficult to close. When primary closure cannot be obtained due to excessive skin tension, consider either immediate or staged flap or graft reconstruction. (see blogs from 3/20/14 on punch skin grafts and 4/1/14 on axial pattern skin flaps) If local tissues are adequate for closure, use the “Rule of Halves” technique (see blog from 11/3/14 on closure of elliptical skin incisions). A towel clamp can be used to initially bring the skin together at the middle of the incision to make suture placement easier.(Fig. 5) 

Fig. 5: A towel clamp is used to temporarily relieve tension and allow
suture closure the incision.

Close deep tissues at the middle of the incision first, then continue to place sutures in the rule of halves manner to achieve complete closure.(Fig. 6, 7)  

Fig. 6: Deep sutures have been placed in the middle of the incision; the next 2 deep sutures
will be placed at the arrows in the "Rule of Halves" manner.

Fig. 7: Final appearance of closed incision

Place a closed suction drain if excessive dead space exists in the deep tissue layers that cannot be closed (see blog from 3/15/14 on Jackson Pratt drains)

After removal of the mass, ink the tissue specimen with appropriate dye such as India ink to allow the pathologist to identify the margins of the excision. Also, place a suture on either the cranial or caudal aspect of the specimen to further orient the pathologist in case one of the margins shows incomplete excision of the tumor.

Postoperative Care

Routine supportive care is administered after removal of mast cell tumors. Avoid NSAIDS administration on MCT dogs to prevent compounding the gastric irritation from the histamine. Tramadol is a good alternative postoperative analgesic. Monitor the surgical incision for swelling or bleeding, and instruct owners to limit exercise and monitor the surgical site carefully at home. Although most dogs and cats recover without major systemic complications after removal of MCT, systemic vascular collapse is possible from massive histamine release in rare cases. Fluid resuscitation and corticosteroid administration may be necessary to support and stabilize the patient if this occurs.

Prognosis

Long-term outcome is dependent upon the histopathologic classification of the MCT. There are 2 major classification schemes now used by pathologists, i.e., Grade 1, 2 and 3 (1 is low grade, 3 is high grade and 2 is intermediate grade) or a simpler 2 tier system of low-grade vs. high grade.(1) Regardless of the system used, the higher the grade of MCT the poorer the prognosis.(1,2) Information on adjunctive therapy such as chemotherapy or radiation therapy is readily available and may be useful in animals with incompletely excised or metastatic tumors.(3)

References

1. Sabattini S, Scarpa F, Berlato D, Bettini G. Histologic grading of canine mast cell tumor: is 2 better than 3? Vet Pathol. 2015 Jan;52(1):70-3.

2. Donnelly L, Mullin C, Balko J, et.al. Evaluation of histological grade and histologically tumour-free margins as predictors of local recurrence in completely excised canine mast cell tumours.Vet Comp Oncol. 2015 Mar;13(1):70-6.

3. London CA, Thamm DH. Mast cell tumor. In: Small Animal Clinical Oncology, eds: Withrow S, MacEwen G, Elsevier, 2013, pg. 335.

Thyroid Cancer in Dogs: Not always a bad disease!

Thyroid neoplasia is fairly common in dogs and is seen more frequently in boxers, golden retrievers, and beagles.(1) The tumors are usually malignant and unilateral however bilateral tumors are possible. Carcinoma is the most common tumor and they can metastasize to lungs and regional lymph nodes.(2) They can also be locally invasive and spread into adjacent vasculature such as the jugular vein. Because of the complex nature of the cervical anatomy and potential invasiveness of thyroid tumors, surgical removal by a board certified veterinary surgeon is recommended.

Clinical Signs

Dogs may be minimally symptomatic and present for a mass in the neck that is either discovered by the owner or found on routine physical examination.(Fig. 1) 

Fig. 1: A West Highland White Terrier with a thyroid  tumor visible in the neck. (arrows)

If early diagnosis is pursued, the tumor may be small, encapsulated, and freely movable in the neck. More advanced tumors can be very large, fixed in position, and encompassing the trachea and larynx.

In rare cases the thyroid tumor is functional and secreting an excessive amount of thyroxine causing hyperthyroidism. Signs of hyperthyroidism include weight loss, increased appetite, polyuria and polydipsia. Cardiac abnormalities such as cardiomyopathy can result from the excessive thyroid hormone secretion. Submit blood samples for thyroid hormone panel to confirm the diagnosis of a functional thyroid tumor.

Diagnosis and Staging

An accurate preoperative diagnosis is important since masses in the neck other than thyroid tumors, such as those involving the salivary glands or lymph nodes, can occur. Carefully palpate the neck mass and regional lymph nodes. Small, well-circumscribed and freely movable tumors are usually amenable to surgical resection.

Fine-needle aspirate or tissue biopsy of the thyroid tumor helps establish the type of tumor. However, recognize that bleeding associated with these procedures can obscure the surgical field and make the procedure more difficult. Ultrasound examination may be helpful to identify the involved thyroid lobes, evaluate for local tissue invasion, and guide fine needle aspiration. Obtain thoracic radiographs to rule out pulmonary metastasis or other cardiopulmonary disorders.

Surgical Procedure

The objectives of surgery are to: completely remove the thyroid mass, preserve at least one parathyroid gland, minimize blood loss, and avoid injury to the recurrent laryngeal nerves, trachea, and esophagus.

Anatomy

The thyroid gland in the dog is divided into 2 lobes that are located adjacent to the trachea and just distal to the larynx.(3) (Fig. 2) 

Fig. 2: Normal anatomy of the cervical region in the dog. Arrows delineate the thyroid lobes.
(Illustration by Mr. Tim Vogt, Medical Illustrator, College of Veterinary Medicine, The Ohio State University)

The normal gland has a pale brown color and is approximately 2 to 2 and 1/2 cm in length.  The principle blood supply to each lobe is the cranial and caudal thyroid arteries, branches of the common carotid artery.  Venous drainage of the thyroid is via the cranial and caudal thyroid veins.

The thyroid gland has a distinct capsule that can be bluntly separated from the parenchyma.  Small blood vessels may be located on the capsule surface and between the capsule and the parenchyma of the gland. Two parathyroid glands are usually associated with each thyroid lobe.  The external parathyroid gland usually lies in the fascia at the cranial pole of the thyroid lobe.  The internal parathyroid gland is usually embedded in the thyroid parenchyma and is variable in location.  The external parathyroid glands are much smaller than the thyroid lobe and can be distinguished from the thyroid tissue by their lighter color and spherical shape. However, the parathyroid gland can be confused with fat.  The blood supply to the parathyroid glands also arises from the cranial thyroid artery.

Overview of Surgical Technique

The dog is placed in dorsal recumbency and the ventral cervical area prepared for aseptic surgery. A ventral midline cervical surgical approach is made from the larynx to the manubrium. The paired sternohyoideus muscles are divided on the midline and retracted. (Fig. 3) A stomach tube or small endotracheal tube in the esophagus helps identify this structure.

Fig. 3: Operative photograph of a unilateral thyroid tumor (arrows)
in a dog with thyroid carcinoma.

Ligate or cauterize the extensive vascular network surrounding the thyroid and carefully dissect out the tumor. Begin dissection at the caudal aspect of the tumor and gradually work cranially. (Fig. 4) 

Fig. 4: Dissection of a thyroid carcinoma in a dog proceeding from
caudal to cranial (black arrow). Yellow arrows indicate the trachea.

Identify the recurrent laryngeal nerves adjacent to the trachea and avoid trauma to them. If possible, identify and preserve the parathyroid glands especially with bilateral thyroidectomy. With large malignant tumors, the parathyroid glands may be difficult to indentify.

Close the muscle routinely with simple continuous, absorbable suture; the subcutaneous tissue with simple continuous, absorbable suture; and the skin with simple interrupted, nonabsorbable suture or an intradermal pattern using absorbable suture.

Postoperative Care and Complications

Short-Term

Closely monitor for hemorrhage or seroma formation at the surgical site. Cold compresses on the incision for the first 24 hours are helpful to prevent swelling.Monitor serum calcium concentrations for at least 2–4 days postoperatively if a bilateral thyroidectomy was performed. Monitor the calcium concentrations longer if the levels are decreasing. Treat hypocalcemia with oral calcium and vitamin D. If bilateral thryoidectomy was performed, evaluate thyroid function and treat hypoparathyroidism if necessary.

Long-Term

Reevaluate the dog frequently (every 3 months for the first year) with physical examinations and thoracic radiographs to monitor for recurrence of the primary tumor and metastasis.
Consider postoperative chemotherapy or radiation therapy if the tumor was malignant and incompletely excised.

Prognosis

Key Point:  Surgical resection of encapsulated, movable thyroid tumor in dogs has been found to result in median postoperative survival of 20 months.

In the study cited above the dogs were treated with surgery alone and had no evidence of metastasis at the time of surgery.(4) As with most cancers, early diagnosis and treatment increases the chances of a good outcome.

References
  1. Birchard SJ, Roesel OF: Neoplasia of the thyroid gland in the dog: A retrospective study of 16 cases. JAAHA 17:369-372, 1981.
  2. Brodey TS, Kelly DF: Thyroid neoplasms in the dog. Cancer 22: 406-416, 1968.
  3. Evans HE, Christensen GC: Miller's Anatomy of the Dog, The Endocrine System, WB Saunders, Philadelphia, 1979, pp. 611-618.
  4. Klein MK1, Powers BE, Withrow SJ, Curtis CR, Straw RC, Ogilvie GK, Dickinson KL, Cooper MF, Baier M. Treatment of thyroid carcinoma in dogs by surgical resection alone: 20 cases (1981-1989).J Am Vet Med Assoc. 1995 Apr 1;206(7):1007-9.