Cisplatin chemotherapy for treatment of thyroid carcinoma in dogs: 13 cases

Sodium iodide symporter immunolabelling as a predictor of clinical iodide uptake in canine thyroid carcinoma: A preliminary study

Thyroid follicular tumours may take up iodide via the sodium-iodide symporter. Knowledge of iodide uptake could then allow treatment with I-131 in dogs with high-risk tumours. The objective of this study was to determine the relationship between clinically detectable iodide uptake (as determined by scintigraphy and/or thyroxine concentrations) and sodium iodide symporter immunohistochemical labelling on histologically fixed thyroid tumours. Nineteen dogs were identified who were diagnosed with thyroid carcinoma and underwent surgery from November 2017 to July 2021. All had recorded thyroid hormone concentrations and were hyperthyroid and/or underwent preoperative nuclear imaging using planar scintigraphy (technetium-99m or I-123), or I-124 PET-CT. All dogs subsequently underwent surgery to remove the thyroid mass. Twenty-two tumours were submitted for histopathologic analysis immediately following surgery, which confirmed a diagnosis of thyroid carcinoma for each tumour. Images and/or thyroid hormone concentrations were reviewed for the included cases, and tumours were sorted into an avid/functional group (group 1) and a non-avid/functional group (group 2). The tumour tissues were re-examined histologically using sodium iodide symporter (NIS) immunohistochemistry (IHC). Group 1 contained 15 avid/functional tumours. Twelve of these tumours had membranous NIS IHC labelling. Group 2 contained 7 non-avid tumours. One of these tumours had membranous NIS IHC labelling. This resulted in an overall sensitivity and specificity for identification of avid/functional tumours with membranous NIS of 80.0% and 85.7%, respectively. NIS IHC may predict ion trapping in canine follicular thyroid tumours. Further studies using iodide-based imaging are warranted to better determine the clinical utility of this diagnostic modality.

Response of canine thyroid carcinomas to radioiodine

Radioactive iodine (¹³¹ I) has previously been reported to prolong survival in dogs with thyroid carcinoma. This study aimed to describe tumour response and progression-free interval (PFI) in dogs with thyroid carcinomas treated with ¹³¹ I. Secondary aims were to describe overall survival time (OST) and prognostic factors. A bi-institutional retrospective review of records identified 66 dogs with thyroid carcinoma treated with ¹³¹ I from January 2010 to April 2020. Response was described using RECIST or a subjective response assessment where specific tumour measurements were not available. Forty-eight dogs (72.7%) were treatment naïve and 18 dogs (27.3%) had received prior therapy at the time of ¹³¹ I treatment. Objective responses were available for 34 dogs and subjective responses for 58 dogs. The overall response rate was 35.3% (four complete and eight partial responses). Improvement of clinical signs was seen in 76.2% of dogs (32/42). Kaplan-Meier-estimated median PFI (95% confidence interval [CI]) was 301 (217-578) days and OST (95% CI) was 564 (421-865) days. Prior therapy was associated with a lower hazard for progression (hazard ratio [HR] 0.260 95% CI 0.123-0.548, p = .0004). Treatment of thyroid carcinoma using ¹³¹ I can effectively alleviate clinical signs and reduce disease burden in a proportion of dogs.

Canine thyroid carcinoma prognosis following the utilisation of computed tomography assisted staging

BACKGROUND

Metastatic disease is frequently present at the time of diagnosis of canine thyroid carcinoma; however, utilisation of computed tomography (CT) alone for staging pre-treatment has been rarely reported in the veterinary literature.

METHODS

The aims of this retrospective study were to stage affected dogs using CT findings of the cervical and thoracic regions, combined with histopathology/cytology results, in order to assess whether metastatic disease/WHO staging was of prognostic significance.

RESULTS

Fifty-eight dogs were included in the study. Classification of cases into WHO stages I, II, III and IV were 10%, 50%, 9% and 31%, respectively. No statistically significant effect of WHO stage classification on overall survival/follow-up time was found (P = .576). Surgery resulted in a statistically significant increase in overall survival/follow-up time (P < .01). There was no statistically significant effect on overall survival/follow-up time in dogs that received medical therapy, either as sole therapy or as an adjunctive post-surgery (P = .198).

CONCLUSION

In summary, this study documents the metastatic rate of canine thyroid carcinoma using CT for staging pre-treatment. Staging utilising CT revealed a higher distant metastatic rate in dogs with thyroid carcinoma when compared to historical studies using different imaging techniques. As long-term outcomes are possible for cases with advanced disease, surgical intervention could still be considered.

Safety and efficacy of stereotactic body radiation therapy (SBRT) for the treatment of canine thyroid carcinoma

Thyroid carcinoma develops spontaneously in dogs, with only 25% to 50% of cases amenable to surgery at diagnosis. Local control for unresectable tumours can be provided with external beam radiotherapy. The aim of this retrospective study is to describe the safety and efficacy of stereotactic body radiation therapy (SBRT) for treatment of canine thyroid carcinoma. Twenty-three dogs met inclusion criteria; median tumour volume before SBRT was 129.9 cm³ (range, 2.7-452.8 cm³ ). Sixteen patients (70%) had unresectable tumours. Pulmonary metastasis was present or suspected in 10 patients (44%) before SBRT. Patients were prescribed 15 to 40 Gy to targeted tumour volume in one to five fractions. Twenty patients evaluated had overall response rate of 70% (complete response, n = 4; partial response, n = 10). Thirteen out of sixteen (81%) symptomatic patients had clinical improvement within a median time of 16 days (range, 2-79 days). Median progression free survival (MPFS) was 315 days. Median survival time (MST) was 362 days. Nine patients (39%) had grade 1 acute radiation toxicity. Three patients had grade 1 late radiation toxicity (two leukotrichia and one [4%] with intermittent cough). Responders had significantly longer MPFS (362 vs 90 days; HR 4.3; 95% CI 1.4-13.5; P = .013) and MST (455 vs 90 days; HR 2.9; 95% CI 1-8.4; P = .053). Presenting with metastasis was not a significant negative prognostic factor (MST 347 vs 348 days without metastasis; P = .352). SBRT is a safe and effective treatment modality for non-resectable canine thyroid carcinoma.

Complications and outcomes associated with unilateral thyroidectomy in dogs with naturally occurring thyroid tumors: 156 cases (2003-2015)

OBJECTIVE

To describe complications and outcomes of dogs undergoing unilateral thyroidectomy for the treatment of thyroid tumors.

ANIMALS

156 dogs undergoing unilateral thyroidectomy for a naturally occurring thyroid tumor.

PROCEDURES

Dogs that underwent a unilateral thyroidectomy in 2003 through 2015 were included in a multi-institutional retrospective study. For each dog, information gathered through evaluation of electronic and paper records included perioperative complications, short-term outcome (survival to discharge from the hospital vs nonsurvival), and long-term outcome (survival time).

RESULTS

In the perioperative period, complications occurred in 31 of the 156 (19.9%) dogs; hemorrhage was the most common intraoperative complication (12 [7.7%] dogs). Five of 156 (3.2%) dogs received a blood transfusion; these 5 dogs were among the 12 dogs that had hemorrhage listed as an intraoperative complication. Immediately after surgery, the most common complication was aspiration pneumonia (5 [3.2%] dogs). One hundred fifty-three of 156 (98.1%) dogs that underwent unilateral thyroidectomy survived to discharge from the hospital. One hundred-thirteen dogs were lost to follow-up; from the available data, the median survival time was 911 days (95% confidence interval, 704 to 1,466 days).

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that unilateral thyroidectomy in dogs with a naturally occurring thyroid tumor was associated with a perioperative mortality rate of 1.9% and a complication rate of 19.9% and that hemorrhage and aspiration pneumonia were the most common complications. Long-term survival of dogs undergoing unilateral thyroidectomy for the treatment of thyroid tumors was not uncommon.

Toceranib phosphate in the treatment of canine thyroid carcinoma: 42 cases (2009-2018)

Thyroid carcinoma is the most common endocrine malignancy in dogs. Thyroidectomy and radiation therapy control local disease, yet are not always feasible, and efficacious medical therapies need to be identified. Toceranib phosphate has been reported to provide clinical benefit (CB) in dogs with thyroid carcinoma, while its role in treatment-naïve thyroid tumours has not been well-described. The objective of this study was to describe the use of toceranib in the management of thyroid carcinomas in dogs in both the naïve-disease and prior therapy- settings. A medical record search identified 42 dogs diagnosed with thyroid carcinoma and treated with toceranib, of which 26 and 16 dogs were in settings of naïve-disease and after prior therapy, respectively. Twenty-three (88.4%) and twelve (75%) dogs experienced CB in the naïve and prior therapy settings, respectively. The median [95% confidence interval] progression free interval (PFI) for dogs in the naïve and prior therapy settings were 206 [106,740] and 1015 [92,1015] days, respectively. The median overall survival time (OST) for dogs in the naïve and prior therapy settings were 563 [246,916] and 1082 [289,1894] days, respectively. Overall, the data provided no evidence for differences in overall PFI (P > .20) or OST (P = .15) between settings. However, when asymptomatic at the time of diagnosis, dogs in the naïve setting showed poorer survival prognosis (estimated hazard ratio 17.2 [1.8, 163]) relative to dogs in the prior therapy setting. This study characterizes PFI, OST and CB with minimal AE in dogs with thyroid carcinoma treated with toceranib in both the naïve and prior therapy settings.

Post-surgical treatment of thyroid carcinoma in dogs with retinoic acid 9 cis improves patient outcome

The objective of the present study was to compare the effects of isotretinoin 9-cis (RA9-cis) as a post-surgery treatment of thyroid carcinoma to a traditional treatment (doxorubicin) and no treatment. Owners who did not want their dogs to receive treatment were placed into the control group A (GA; n=10). The remaining dogs were randomly placed into either group B (GB; n=12) and received doxorubicin at a dose of 30 mg/m² every three weeks, for six complete cycles or group C (GC; n=15) and treated with RA9-cis at a dose of 2 mg/kg/day for 6 months. The time of the recurrence was significantly shorter in the GA and GB compared to GC (P=0.0007; P=0.0015 respectively), while we did not detect differences between GA and GB. The hazard ratio of recurrence between GA and GB compared to GC were 7.25 and 5.60 times shorter, respectively. We did not detect any differences between the other groups. The risk ratio of recurrence was 2.0 times higher in GA compared to GC and 2.1 times higher in GB compared to GC. The type of carcinoma had an effect on time of survival with follicular carcinomas having an increased mean survival time than follicular-compact carcinomas (P<0.0001) and follicular-compact carcinomas had a longer mean survival time than compact carcinomas. The interaction among treatment and type was significant, but survival time in follicular carcinomas did not differ between treatments. In follicular-compact carcinomas the survival time of GC was greater than GB (P<0.05), but we did not detect a difference between GA and GB. In conclusion, this study shows that the use of surgery in combination with RA9-cis treatment significantly increases survival rate and decreases the time to tumor recurrence when compared to doxorubicin treated or untreated dogs. The histological type of carcinoma interacted with treatment for time to recurrence and survival time, with more undifferentiated carcinomas having a worse prognosis than differentiated carcinomas.

Immunohistochemical expression of potential therapeutic targets in canine thyroid carcinoma

BACKGROUND

Thyroid carcinoma is a common endocrine tumor in the dog. Local invasive growth frequently precludes surgical excision and, in up to 38% of dogs, the tumor has already metastasized by the time of diagnosis. Therefore, it is important to investigate new treatment modalities that may be useful for the large number of dogs with inoperable tumors or metastatic disease.

HYPOTHESIS/OBJECTIVES

To investigate the immunohistochemical expression of potential therapeutic targets in canine thyroid tumors.

ANIMALS

74 dogs with thyroid neoplasia.

METHODS

Immunohistochemistry was performed for thyroglobulin, calcitonin, vascular endothelial growth factor (VEGF), p53, cycloxygenase-2 (cox-2), and P-glycoprotein (P-gp).

RESULTS

Fifty-four (73%) tumors were classified as follicular cell thyroid carcinomas (FTCs) and 20 (27%) as medullary thyroid carcinomas (MTCs). Eighty percent of FTCs and all MTCs had a high percentage (76-100%) of neoplastic cells immunopositive for VEGF. Thirteen percent of FTCs and 50% of MTCs expressed cox-2. Seven percent of FTCs and 70% of MTCs expressed P-gp. No tumor was immunopositive for p53 expression. Expression of VEGF (P = .034), cox-2 (P = .013), and P-gp (P < .001) was significantly higher in MTCs compared to FTCs.

CONCLUSIONS AND CLINICAL IMPORTANCE

VEGF is a potential therapeutic target in both FTC and MTC in dogs. Cox-2 and P-gp may be useful molecular targets in canine MTC.

Thyroid Cancer in Dogs: An Update Based on 638 Cases (1995–2005)

The goal of this study was to update the descriptive statistics of thyroid cancer by using data from multiple institutions collected through the Veterinary Medical Database (VMDB). Information was collected and reported from cases of canine thyroid cancer submitted to the VMDB between January 1, 1995 and December 31, 2005. Odds ratio (OR) analysis was performed on breeds that had ≥3% of the total number of dogs with thyroid cancer; ORs for each age category were also determined. Thyroid cancer represented 1.1% of all neoplasms during the time period of interest. Golden retrievers, beagles, and Siberian huskies all had significantly increased ORs for developing thyroid cancer. No sex predisposition was evident, but dogs between 10 and 15 years of age had a significantly increased chance of developing thyroid disease. Carcinomas and adenocarcinomas represented 90% of thyroid cancers, while adenomas represented 9.3%. Thyroid carcinoma and adenocarcinoma continue to be uncommon in our canine population. Older dogs are still more commonly affected, and this study is in agreement with previous studies that golden retrievers and beagles are overrepresented. A new finding is that Siberian huskies are also overrepresented. Carcinomas represent a much higher proportion of thyroid cancers than previously reported, and adenomas are likely incidental findings on necropsy. Thyroid cancer should be high on the list of differentials for a neck mass in older, large-breed dogs, as they make up 1.1% of the cancer cases reported. The overwhelming majority of thyroid cancers are carcinomas, and they are most common in golden retrievers, beagles, and Siberian huskies.

In vitro and in vivo evaluation of combined calcitriol and cisplatin in dogs with spontaneously occurring tumors

PURPOSE

Calcitriol potentiates cisplatin-mediated activity in a variety of tumor models. We examine here, the effect of calcitriol and cisplatin pre-clinically and clinically in canine spontaneous tumors through in vitro studies on tumor cells and through a phase I study of calcitriol and cisplatin to identify the maximum-tolerated dosage (MTD) of this combination in dogs with cancer and to characterize the pharmacokinetic disposition of calcitriol in dogs.

METHODS

Canine tumor cells were investigated for calcitriol/cisplatin interactions on proliferation using an MTT assay in a median-dose effect analysis; data were used to derive a combination index (CI). Cisplatin was given at a fixed dosage of 60 mg/m2. Calcitriol was given i.v. and the dosage was escalated in cohorts of three dogs until the MTD was defined. Serum calcitriol concentrations were quantified by radioimmunoassay.

RESULTS

In vitro, CIs < 1.0 were obtained for all combinations of calcitriol/cisplatin examined. The MTD was 3.75 microg/kg calcitriol in combination with cisplatin, and hypercalcemia was the dose-limiting toxicosis. The relationship between calcitriol dosage and either Cmax or AUC was linear. Calcitriol dosages >1.5 microg/kg achieved Cmax > or = 9.8 ng/mL and dosages >1.0 microg/kg achieved AUC > or = 45 h ng/mL.

CONCLUSIONS

Calcitriol and cisplatin have synergistic antiproliferative effects on multiple canine tumor cells and high-dosages of i.v. calcitriol in combination with cisplatin can be safely administered to dogs. Cmax and AUC at the MTD 3.75 microg/kg calcitriol exceed concentrations associated with antitumor activity in a murine model, indicating this combination might have significant clinical utility in dogs.

Canine thyroid carcinoma

Malignant thyroid carcinomas are relatively common in dogs. The majority of tumors are unilateral and nonfunctional. Before deciding on treatment options, it is important to determine whether the tumor is freely moveable or fixed and invasive into adjacent tissues. Thyroidectomy is recommended for unilateral, mobile thyroid carcinomas. Radiation therapy or radioactive iodine therapy are recommended for dogs with invasive or bilateral thyroid carcinomas. The role of adjunctive chemotherapy is poorly defined, but should be considered in dogs with high-risk tumors, such as large or bilateral thyroid carcinomas. The prognosis is good following surgical treatment of mobile thyroid tumors and irradiation of fixed thyroid carcinomas, with median survival times greater than 3 years.

Thyroid Tumors in Dogs and Cats

The clinical presentation and biologic behavior of thyroid tumors vary widely among dogs, cats, and human beings. Although thyroid tumors in dogs are rare, they are most likely to be malignant. Clinical signs are usually the result of impingement on surrounding structures, and clinical hyperthyroidism is rare. In contrast, hyperthyroidism resulting from benign thyroid proliferation is relatively common among older cats. Malignant tumors are extremely uncommon but have high metastatic potential. Irrespective of the tumor's ability to produce functional thyroid hormone, scintigraphy is often helpful in the diagnosis and staging of thyroid tumors in all three species. Treatment with surgery is a reasonable treatment option for noninvasive tumors. Iodine 131 is a well-established treatment for thyroid nodules in cats, but its effectiveness in dogs is controversial. In dogs, external beam radiation therapy has produced more consistent results in affording local tumor control when surgery is not possible.

Nuclear Imaging and Radiation Therapy in Canine and Feline Thyroid Disease

The indications, techniques, and expectations for radionuclide diagnostic studies on canine and feline thyroid glands are presented. In addition, the considerations surrounding radioiodine or external beam radiotherapy for benign and malignant thyroid disease are reviewed. The intent of this article is to familiarize primary care veterinarians with the utility of and outcome of the ionizing radiation-based diagnostic and therapeutic techniques for assessing and treating canine and feline thyroid disease.

Palliative intravenous cisplatin treatment for concurrent peritoneal and pleural mesothelioma in a dog

A 10-year-old Maltese dog was presented with abdominal distention and dyspnea. Cytological examination of pleural and peritoneal effusion was suggestive of malignant effusion of glandular origin. Numerous, multifocal, tan to white nodules were disseminated throughout the surface of the abdominal organs and peritoneum at biopsy. Histologically, the tumors were revealed to be an epithelial type of mesothelioma. Neoplastic cells co-expressed cytokeratin and vimentin. Intravenous administration of cisplatin was chosen as the treatment. During treatment, the dog's overall body condition improved and the clinical signs were relieved without significant side effects. The survival time from diagnosis to sudden death by unknown cause was 153 days.

Functional thyroid gland adenoma in a dog treated with surgical excision alone

An 11-year-old male Golden Retriever presented with progressive weight loss, tachycardia, hyperthermia, polyuria and polydipsia. A freely movable mass, 4.5 x 4 cm in size, was palpated at the cranioventral cervical region. Hormonal study revealed high levels of serum thyroid hormones, and a tentative diagnosis of hyperthyroidism due to a thyroid tumor was made. The tumor was removed surgically and diagnosed histopathologically as thyroid gland adenoma. Serum thyroid hormone levels decreased after surgery with improved clinical signs. At 12 months after surgery, the dog maintained a good physical condition with no evidence of recurrence.

Acute severe hemorrhage secondary to arterial invasion in a dog with thyroid carcinoma

A 7-year-old spayed female Labrador Retriever was referred because of progressive swelling and bruising of the neck, hemothorax, a possible mediastinal mass, and stridor. At the time of admission, the dog was recumbent, mentally dull, tachycardic, and hypothermic. Fluid therapy with hydroxyethyl starch and a balanced electrolyte solution was administered because of presumed hypovolemic shock secondary to hemorrhage; multiple units of packed RBCs and fresh frozen plasma were also administered. On the basis of the computed tomographic images, extensive subcutaneous, subfascial, and cranial mediastinal hemorrhage; hemothorax; prescapular lymphadenopathy; and a contrast-enhancing mass in the left cranioventral aspect of the neck were diagnosed. Exploratory surgery of the neck was performed. All subcutaneous structures were encased in a large blood clot. During dissection of the clot, pulsatile bleeding was observed just caudal to and to the left of the larynx; ligation of the left common carotid artery resulted in immediate cessation of the pulsatile bleeding. Further surgical exploration revealed a 2.5 x 2.5-cm mass adhered to the left common carotid artery at the level of the branching to the left cranial thyroid artery. The mass was removed; the histologic diagnosis was thyroid carcinoma. Three weeks after surgery, treatment with a combination of radiation and chemotherapy (doxorubicin and carboplatin) was begun. Thirteen months after surgery, the dog continued to be free from clinical signs of disease.

Multimodality therapy for head and neck cancer

The refinement of radiation therapy techniques should result in a decrease in morbidity in canine and feline nasal carcinoma patients and should further allow for the addition of adjuvant therapies. Patients with large oral tumors that are incompletely excised should have radiation therapy added to their treatment regimen. Tumors with significant metastatic potential, such as melanoma, should be considered for addition of chemotherapy. Carboplatin has activity in melanomas and is being added at several institutions, but trial results are not yet available. Chemoradiation has become the treatment of choice for human head and neck squamous cell carcinomas but remains largely unexplored in veterinary medicine. Hopefully, development of chemoradiation will benefit feline squamous cell carcinoma patients, because current treatment regimens are largely ineffective. Immunotherapy agents and targeted biologic therapeutics seem to hold promise for the future.

Computer-assisted image analysis of neovascularization in thyroid neoplasms from dogs

OBJECTIVE

To develop a computer-assisted image analysis procedure for quantitation of neovascularization in formalin-fixed paraffin-embedded specimens of thyroid gland tissue from dogs with and without thyroid gland neoplasia.

SAMPLE POPULATION

47 thyroid gland carcinomas, 8 thyroid gland adenomas, and 8 specimens of thyroid tissue from dogs without thyroid gland abnormalities (normal).

PROCEDURE

Serial tissue sections were prepared and stained with antibodies against human CD31 or factor VIII-related antigen (factor VIII-rag). The areas of highest vascularity were identified in CD31-stained sections, and corresponding areas were then identified in factor VIII-rag-stained sections. Image analysis was used to calculate the total vascular density in each section, and neovascularization, expressed as a percentage, was determined as the absolute value of the total vascular density derived from factor VIII-rag-stained sections minus the vascular density derived from CD31-stained sections.

RESULTS

Mean vascular density of thyroid gland carcinomas derived from CD31-stained sections was significantly greater than density derived from factor VII I-rag-stained sections. This incremental difference was presumed to represent degree of neovascularization. However, significant differences were not detected between vascular densities derived from CD31 and factor VIII-rag-stained sections for either normal thyroid gland tissue or thyroid gland adenomas. No significant correlations were found between vascular density in thyroid gland carcinomas and survival time following surgery.

CONCLUSION AND CLINICAL RELEVANCE

A computer-assisted image analysis method was developed for quantifying neovascularization in thyroid gland tumors of dogs. This method may allow identification of dogs with tumors that are most likely to respond to treatment with novel antiangiogenesis agents.

Definitive radiation therapy for infiltrative thyroid carcinoma in dogs

The medical records of eight dogs with histopathologically confirmed infiltrative thyroid carcinoma treated with external beam radiation were reviewed and a retrospective analysis of survival and local tumor control were performed. The dogs received a definitive radiotherapy protocol of 46.8-48 Gray. All dogs had a reduction in tumor size to a clinically undetectable level on follow up examinations. Kaplan-Meier analysis indicated a median survival time of 24.5 months. Pulmonary metastasis was detected in three dogs and one of these dogs had concurrent bone metastasis. One dog had bone metastasis alone. Two dogs were alive at the censor. This study suggests that fractionated, definitive radiation therapy using multiple, moderate doses of radiation is an effective treatment for local control of invasive thyroid carcinoma in dogs.

Endocrine tumors

Because of the diverse nature of endocrine organs, and their vast range of physiologic functions, endocrine tumors encompass a wide range of origination sites and disease entities. The clinical picture of affected individuals is highly dependent on the tissue of origin, and the presence or absence of functional hormone secretions. Identification, localization, and therapeutic strategies, as well as prognosis can vary greatly. Many endocrine tumors have been described in human as well as veterinary patients. This article focuses on endocrine tumors of dogs and cats. Various tumors affecting the pancreas, thyroid, parathyroid, adrenal and pituitary glands are described, including insulinoma, gastrinoma, glucagonoma, and thyroid carcinoma, as well as parathyroid hormone- and growth hormone-secreting tumors. The syndrome of multiple endocrine neoplasia is also described.

Prognostic factors and patterns of treatment failure in dogs with unresectable differentiated thyroid carcinomas treated with megavoltage irradiation

OBJECTIVE

To determine quality and duration of progression-free survival (PFS) time in dogs with unresectable thyroid carcinomas treated with definitive megavoltage irradiation and analyze prognostic factors of PFS and patterns of failure (local recurrence vs metastasis).

DESIGN

Prospective clinical trial.

ANIMALS

25 dogs with locally advanced thyroid carcinomas and no evidence of metastasis.

PROCEDURE

Dogs were treated with 48 Gy during 4 weeks on an alternate-day schedule of 4 Gy/fraction.

RESULTS

Irradiation was safe and effective for treatment of large unresectable thyroid carcinomas. Progression-free survival rates were 80% at 1 year and 72% at 3 years. Time to maximum tumor size reduction ranged from 8 to 22 months. Factors affecting PFS were not found. Twenty-eight percent (7/25) of dogs developed metastasis. Dogs with bilateral tumors had 16 times the risk of developing metastases, compared with dogs with a single tumor. Dogs with no evidence of tumor progression had 15 times less risk of developing metastases. Radiation-induced hypothyroidism was suspected in 2 dogs 13 and 29 months after irradiation.

CONCLUSIONS AND CLINICAL RELEVANCE

Irradiation is effective for local control of thyroid tumors, despite their slow regression rate. Results provided evidence that local tumor control affects metastatic outcome in dogs with thyroid carcinomas and is a strong basis for the development of new approaches that include irradiation in the management of dogs with advanced thyroid carcinomas. Improvements in local tumor control alone may be insufficient to improve survival times because of the high risk of metastatic spread before an initial diagnosis is made, which warrants initiation of early systemic treatment.

Hypofractionated radiation therapy for invasive thyroid carcinoma in dogs: a retrospective analysis of survival

Thirteen dogs with invasive thyroid carcinoma (WHO classification T2b or T3b) seen between January 1991 and October 1997 were treated by external beam irradiation. Four once-weekly fractions of 9 gray of 4 MeV X-rays were administered. Four of the dogs died of progression of the primary disease and four from metastatic spread. Of the remaining dogs, three died of unrelated problems, although two were still alive at the time of the censor. Kaplan-Meier analysis of the survival time from first dose to death from either primary or metastatic disease gave a median survival time of 96 weeks (mean 85 weeks, range six to 247 weeks). Radiographic evidence of pulmonary metastatic disease at presentation had no prognostic value whereas crude growth rate was a highly significant factor. The present series indicates that radiation therapy should be considered an important modality for the control of invasive thyroid carcinoma in the dog.