"Thyroid Adenocarcinoma" TUMOR TIDBITS, A BIWEEKLY VETERINARY ONCOLOGY E-LETTER Number 67; August 30, 2002. Editor: Kevin A. Hahn, DVM, PhD, Dipl - ACVIM (Oncology) & Overall Nice Guy! ANNOUNCEMENTS *Did you know that thyroxine can be used as a treatment for thyroid cancer in dogs? *The Annual Meeting of the Veterinary Cancer Society is coming up soon, check www.vetcancersociety.org for details and notes! *We're revising our web site! Check regularly for updates or call us at any time! ======================================================================= THIS WEEK'S TUMOR TIDBIT: THYROID ADENOCARCINOMA ======================================================================= OVERVIEW *Thyroid adenocarcinoma is a malignant neoplasm arising from the thyroid gland. *Usually not functional but highly invasive and metastatic *Affects the thyroid gland and surrounding soft tissue (e.g., esophagus and trachea) *Common metastatic sites are lungs and regional lymph nodes *Predilection for boxers, golden retriever, and beagle *Median age and range variably reported 0-9.6 years (range, 4-18 years) *Characterized by rapid invasive growth and usually diagnosed when disease is advanced *Most tumors (65-70%) unilateral SIGNS & SYMPTOMS *Cervical mass dyspnea, dysphagia, or dysphonia *Less frequently, regurgitation, precaval syndrome, weight loss, and excessive hemorrhage secondary to disseminated intravascular coagulation (DIC) *Hyperthyroidism characterized by polyuria, polydipsia, and weight loss despite a normal-to-high food intake *Hypothyroidism characterized by weakness, lethargy, and poor hair coat *Firm, nonpainful, movable or fixed neck mass *About 2/3 of thyroid carcinomas are unilateral. DIFFERENTIAL DIAGNOSES *Abscess *Granuloma *Salivary mucocele *Metastatic tonsillar squamous cell carcinoma *Lymphosarcoma *Carotid body tumor *Other soft tissue sarcoma DIAGNOSTIC APPROACH & FINDINGS *Laboratory results usually normal *Consider thoracic radiographs to check for metastasis *Consider cervical radiographs to identify location of the mass, proximal airway, and esophagus before performing a biopsy *Consider thyroid gland scintigraphy (99mTc-pertechnetate) imaging to delineate location of the tumor(s), including ectopic tumors and metastases. *Radioiodine studies with 131I or 125I provide similar information and can also determine functional status of the tumor. *Cytologic examination of fine-needle aspirate of mass to rule out nonthyroid disease; blood contamination is a relatively constant feature because of the vascular nature of thyroid tumors. *Cytologic examination of the regional lymph nodes is done for staging purposes. *Biopsy and histologic evaluation is required for definitive diagnosis. Bleeding can be a problem during biopsy. *Tumors are typically poorly encapsulated and local invasion into the wall of the trachea, esophagus, larynx, surrounding Iymphatic vessels, and blood vessels SURGICAL CONSIDERATIONS *Complete surgical excision treatment of choice for freely moveable carcinoma *Examine cervical lymph nodes closely and remove or biopsy if indicated *Carefully inspect the contralateral gland because approximately 33% of thyroid carcinomas are bilateral *Invasive thyroid carcinoma impossible to remove completely but may be debulked and biopsied *Invasive tumor amenable to surgical removal after external beam radiotherapy or systemic chemotherapy in some patients NONSURGICAL CONSIDERATIONS *Doxorubicin (30 mg/M2 IV over 20-30 min q3wk for a total of 5 treatments) reported to effect partial regression in about 50% of patients *Maintenance dosage of thyroxine (20-40 mcg/kg q24h) has been recommended to suppress pituitary production and release of thyroid stimulating hormone. *The theoretical benefit derived from this treatment has not been evaluated in dogs. *Cisplatin (60 mg/M2) has had limited use for managing thyroid carcinoma; further study is warranted. *Radiotherapy has been used for treatment of nonresectable tumors. The efficacy of preoperative versus postoperative radiotherapy has not been determined. *Radioactive iodine (131I) has been used in dogs with hyperfunctioning tumors. The efficacy of this treatment has not been determined. PATIENT MONITORING *Serum calcium concentration is monitored after bilateral thyroidectomy. Patient with signs of hypocalcemia (i.e., nervousness, irritability, panting, high body temperature, muscle tremors, tetany, pruritis, and convulsions) should receive 10% calcium gluconate IV (1.0-1.5 ml/kg IV over 10-20 min). *Vitamin D administered orally (dihydrotachysterol) after emergency treatment *Thyroid hormone replacement (i.e., L-thyroxine or sodium levothyroxine) usually required after bilateral thyroidectomy EXPECTED COURSE AND PROGNOSIS *Factors that have the biggest influence on prognosis include the total tumor volume of the primary tumor, the degree of local invasion, the number and extent of regional Iymph node involvement, and the presence of distant metastases. Of dogs with thyroid carcinoma < 20 cm3, < 20% have metastatasis; of dogs with tumor > 21 cm3, 75% have metastasis. ASSOCIATED CONDITIONS *Many dogs with thyroid adenocarcinoma develop other primary tumors. Most common are chemodectoma, perianal gland adenoma, mast cell tumor, lipoma, and adrenal adenoma. The syndrome of multiple endocrine neoplasia consisting of medullary carcinoma, pheochromocytoma, and parathyroid hyperplasia has also been reported in dogs. WHAT DO WE DO AT GULF COAST VETERINARY ONCOLOGY? *Surgical removal is still considered the treatment of choice and should be considered. If a tumor is not surgically removable, we use radiation therapy to shrink the tumor so that surgery may be considered or the use of Adriamycin. In all situations, we recommend concurrent use of thyroxine as a lifetime chemoprevention for the development and growth of metastatic disease. SUGGESTED READING * The 5 Minute Veterinary Consult. By Tilley LP & Smith FWK. Lippincott, William & Wilkins, 2002. * Veterinary Oncology, From "The Practical Veterinarian Series". By Hahn KA. Butterworth-Heinemann Press, 2002. ======================================================================= Hope this info helps and don't hesitate to call us Gulf Coast Veterinary Oncology! Kevin A. Hahn, DVM, Phd, Diplomate ACVIM (Oncology), drhahn@gcvs.com Janet K. Carreras, VMD, Diplomate ACVIM (Oncology), drcarreras@gulfcoastvetspec.com Glen K. King, DVM, MS, Diplomate ACVR (Radiology & Radiation Therapy), drking@gcvs.com Gulf Coast Veterinary Diagnostic Imaging & Oncology 1111 West Loop South, Suite 150, Houston, TX 77027 P: 713.693.1166 F: 713.693.1167 W: www.gcvs.com