Introduction

Goats are an increasingly popular pet animal in the US. Pet goats are often managed differently and reach an older age compared to goats used as production animals. Owners of pet goats are often willing to invest more resources in diagnosis and treatment of chronic or complex disease conditions such as neoplasia. However, unlike in small-animal or equine medicine in which neoplastic diseases are better understood, there are limited published data on clinical presentation, treatment, or outcome in goats with neoplasia.

Specific caprine neoplasms have been described in case reports and a limited number of retrospective analyses.^1–6 Yau and Rissi⁷ reported a case of a goat with cholecystic adenocarcinoma and insulinomas, and 2 cases of leiomyosarcoma in related Saanen does have been described. Hill et al⁶ reported the clinical signs, signalment, treatment, and outcomes of 13 cases of goats diagnosed with thymomas over a 24-year period. While that study⁶ was useful in describing clinical signs associated with thymomas, it was limited to 1 type of thoracic neoplasia and had a limited number of animals. Furthermore, clinical signs and outcomes of other neoplasms such as mammary gland carcinomas have only been reported in case reports involving a single animal.^3,8,9 A 25-year retrospective analyzed goat neoplasia on the basis of biopsy or necropsy submissions to a veterinary diagnostic lab.¹⁰ That study¹⁰ summarized types of neoplasm in different breeds of goats, but because it was based on necropsy data, it did not include information on the antemortem clinical aspects of neoplasia in goats. Further investigation needs to be done to confirm, compare, and widen the findings of these papers as well as to expand the number of cases available in the literature to strengthen confidence in clinical presentations, treatments, and outcomes of neoplastic processes.

While some neoplasia can be diagnosed using routine testing common to most veterinary practices, goats that have unusual clinical signs, failed to respond to treatment, or have an advanced disease process are often referred to veterinary teaching hospitals for advanced diagnostics and treatment. While some diagnostic and treatment techniques can be extrapolated from other species, the clinical manifestation and response to treatment of goats with neoplasia remain largely undetermined. The objectives of this retrospective study were to identify goats definitively diagnosed with neoplasia at a veterinary teaching hospital over a 15-year period and describe their presenting complaint, diagnostic testing, treatment, and short- and long-term outcomes. The results of this study can help increase awareness of neoplasia in the expanding pet goat population and provide veterinarians with information to help guide clinical decision-making in goats diagnosed with neoplasia.

Materials and Methods

The medical record databases at the Colorado State University Veterinary Teaching Hospital were systematically reviewed to identify goats admitted to the hospital between March 2007 and March 2022 that were definitively diagnosed with neoplasia. Definitive diagnosis was made by antemortem (fine-needle aspirate [FNA] or biopsy) or postmortem (tissues collected during a necropsy) sample collection and cytologic or histopathologic evaluation by a board-certified American College of Veterinary Pathologists clinical or anatomic pathologist. Goats submitted directly to the Veterinary Diagnostic Laboratory for necropsy without a clinical evaluation were excluded. Goats evaluated by the teaching hospital antemortem and all neoplasms, including those considered incidental, were reported. The medical record for each goat was reviewed, and the following items were extracted: signalment, presenting complaint, breeding history (for does), duration of clinical signs, testing that resulted in a neoplasia diagnosis, evidence of metastasis, treatment, and short-term outcome. Short-term outcome was defined as survival to discharge. Long-term outcome was obtained by contacting owners via email or phone.

Results

A total of 1,441 goats were evaluated at the Colorado State University Veterinary Teaching Hospital during the study period. Forty-six goats were definitively diagnosed with 58 neoplasms via histopathology or cytologic evaluation of FNA samples, making the prevalence of neoplasia within the caprine patient population 3.2%. Eleven goats had 2 distinct tumor types and 1 goat had 3. The median age at the time of diagnosis was 8 years (range, 3 to 17 years). Sex distribution was 38 female (83%), 7 castrated male (15%), and 1 spayed female (2%). The most commonly represented breeds were Nubian (n = 10), Saanen (7), and Pygmy (6). Other breeds included Nigerian Dwarf (n = 3), Alpine (3), Cashmere (2), Angora (2), La Mancha (1), Boer (1), Oberhasli (1), Tennessee Fainting (1), and mixed breed or unknown breed (9). When compared to the total population of goats admitted to the Veterinary Teaching Hospital during the study period, the Saanen breed was overrepresented (P < .0001) but the Nubian breed was not (P = .12). Medical imaging modalities used for tumor identification or metastasis evaluation or both included radiography and ultrasonography. Computed tomography was performed in 3 goats. Evidence for metastases was most commonly sought by performing thoracic radiographs or finding metastatic lesions on postmortem examination.

Clinical signs, duration of clinical signs prior to presentation, and tumor location are summarized (Table 1). The most commonly identified neoplasms were squamous cell carcinoma (SCC) followed by thymoma and mammary carcinoma.

Uterine neoplasia

Six goats (6/46 [13%]) in the study were diagnosed with uterine neoplasia. The median age at time of diagnosis was 7.25 years (range, 4 to 10 years). Of these, 3 (3/6 [50%]) goats were of the Pygmy breed and the Pygmy breed was overrepresented (P = .02). Other breeds included Nigerian Dwarf (n = 1), Cashmere (1), and mixed breed (1). Common clinical presentations and duration of clinical signs prior to presentation are summarized (Table 1). Uterine neoplasia can be difficult to diagnose via ultrasonography, as often these heterogeneous masses are hard to trace back to a likely irregular uterus (Figure 1). Four of the uterine neoplasms were leiomyosarcoma (4/6 [67%]) with the remaining neoplasms identified as leiomyofibroma (1/6 [17%]) and mural round cell tumor (1/6 [17%]). Four goats also had 1 other distinct neoplasm identified at necropsy including 2 pituitary adenomas, a cranial mediastinal thymoma, and an adenocarcinoma of the liver. Ovariohysterectomy was performed in 3 of 6 (50%) of the goats. All 3 were euthanized intraoperatively because the uterine mass was deemed nonresectable. Medical management with 3 prostaglandin trials (dinoprost tromethamine; 2.5 to 5 mg, IM, q 12 to 24 h for 1 to 3 days) and prednisone (tapering course over 4 weeks with starting dose of 0.45 mg/kg, PO, q 24 h followed by maintenance dosage of 0.2 mg/kg, PO, q 24 h for 6 months) was attempted in 1 goat. This animal was treated for 14 months but was eventually euthanized 2 years after diagnosis due to worsening clinical signs. Humane euthanasia without attempted treatment was elected in 2 of 6 animals due to poor condition of the animal.

Ultrasonographic image of a heterogenous soft tissue mass (arrows) with a pocket of anechoic fluid (arrowheads) in the caudal abdomen of a doe, bordered cranially by peritoneal fluid (asterisk).

Citation: Journal of the American Veterinary Medical Association 261, 5; 10.2460/javma.22.11.0530

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Ultrasonographic image of a heterogenous soft tissue mass (arrows) with a pocket of anechoic fluid (arrowheads) in the caudal abdomen of a doe, bordered cranially by peritoneal fluid (asterisk).

Citation: Journal of the American Veterinary Medical Association 261, 5; 10.2460/javma.22.11.0530

• Download Figure
• Download figure as PowerPoint slide

Ultrasonographic image of a heterogenous soft tissue mass (arrows) with a pocket of anechoic fluid (arrowheads) in the caudal abdomen of a doe, bordered cranially by peritoneal fluid (asterisk).

Citation: Journal of the American Veterinary Medical Association 261, 5; 10.2460/javma.22.11.0530

• Download Figure
• Download figure as PowerPoint slide

Discussion

The present study identified several interesting clinical aspects of neoplasia in a primarily pet goat population. One notable finding was the low prevalence of neoplasia (3.2%) within the goat study population. In contrast, a previous investigation¹⁰ found a higher prevalence of 8.7% in samples submitted to a diagnostic lab for necropsy or histopathology. The present study looked at confirmed cases of neoplasia in goats that presented for clinical evaluation at a veterinary teaching hospital. The lower prevalence of 3.2% was surprising because Colorado State University sees a primarily older pet goat population and serves as a referral center for unusual or challenging cases. Both features would seem likely to increase the number of goats with neoplasia within the patient population. Unfortunately, there are limited data reporting the prevalence of neoplasia in goats in other patient populations, making it difficult to surmise whether neoplasia is underdiagnosed in clinical settings or, more specifically, in pet goats.

Many of the goats in the present study were kept as pets rather than production animals. Pet goats often have a longer life-span and owners who are not constrained by the need for their goat to be economically productive. Neoplasms that affect fertility, weight gain, and lactation may be diagnosed sooner when the animal’s productivity is more closely monitored in a production setting. For example, goats with infertility due to uterine neoplasia would likely be recognized sooner in a production setting than in a pet goat that is not regularly bred. However, goats in production settings that become ill or show an unexplained drop in production are more likely to be culled from the herd without pursuing a diagnosis.

One large-scale investigation¹⁰ of neoplasia in goats found some similarities with the present study. One similarity was the age of affected goats with a median age of 8 in the present study compared to the previously reported 7 years. This finding was not surprising because neoplasia is generally uncommon in young animals. Another notable similarity was identifying Saanens and Nubians as the most commonly affected breeds. This was particularly noteworthy in the present study in which Saanen goats were not the most common breed in the general goat patient population. Saanens living in Colorado with their light pigmentation are likely at higher risk than other darker pigmented breeds for developing SCC. Nubian does made up half of the mammary tumor group in the present study, which was similar to the 3 of 7 observed by Löhr¹⁰ when describing does with mammary carcinomas. A case report³ of a mammary adenocarcinoma has also been described in a Nubian buck. Of the 10 does with mammary tumors in the present study, 3 had kidded at least once, 4 had never been bred, and 3 had unknown breeding histories. Further studies may be warranted to investigate a correlation between milking breeds as well as the significance of lactation status on mammary tumors.

A large portion (14/58 [24%]) of neoplasms in the present study were SCC, but the prevalence of SCC within the goat study population was similar to what has been reported in sheep¹¹ and goats.¹² One of the few reports looking at the prevalence of SCC in goats published a prevalence of 5.8% and 0.75% on 2 separate Brazilian farms.¹² Another study investigating SCC in Australian farmed sheep found a prevalence of 0.12% to 4%.¹¹ The prevalence of SCC in the present study, which evaluated patients that were presented to a teaching hospital, was similar to these findings at 1% (14/1,441). This suggests that SCC is a common type of neoplasm in goats but not a commonly diagnosed condition. This discrepancy is likely to be true for other neoplasms as well. It is possible that SCC in goats is even less common in other geographic locations. The high elevation around Fort Collins, Colorado (1,519 m), with greater radiation exposure likely increases the risk of SCC, especially in lightly pigmented animals like Saanens. Lack of skin pigmentation and high UV light exposure have been shown to be predisposing factors for the development of SCC due to increased cellular mutations.¹³ Therefore, not unexpectedly, 87% of goats with SCC had white hair coats. Additionally, goats with SCC are often treated initially by local veterinarians and only referred if lesions are more advanced. Because the Colorado State University livestock clinic serves as both a referral and primary care facility, it is possible that goats with SCC are seen for both initial diagnosis and treatment as well as in cases of advanced disease or poor response to prior therapy.

Treatments for goats with SCCs are presented (Table 2). The majority of goats had surgical excisions performed, a few with adjunctive cryotherapy (1 to 2 sessions/goat) or radiation therapy (intraoperative brachytherapy; n = 1). Lesion size was not consistently available in the medical records. In 1 study⁴ of SCC in goats, lesion resolution was hypothesized to be more closely related to size of the initial mass as opposed to treatment performed, emphasizing the importance of early treatment to achieve remission. Medical management of SCC was attempted in 2 goats. One was treated with meloxicam (1.25 mg/kg, PO, q 24 h) and the other with piroxicam (0.3 mg/kg, PO, q 24 h). Neither of these resulted in mass resolution. The goat treated with meloxicam was euthanized 3 weeks after initiation of medical management for a suspected acute kidney injury diagnosed on necropsy. The goat treated with piroxicam was euthanized at an unknown time following initial treatment for continued mass growth. Research has shown that piroxicam may be useful in the treatment of oral SCC in dogs¹⁴; however, to the authors’ knowledge, there have been no studies to date evaluating the efficacy of piroxicam for treatment of SCC in livestock species. Further studies on caprine SCC investigating lesion size and response to treatment are needed.

Udder enlargement was the main clinical sign in goats with mammary neoplasia and goats diagnosed with pituitary tumors. In humans with pituitary tumors, prolactin produced by the anterior pituitary gland is often upregulated, leading to galactorrhea.¹⁵ It is possible that a similar process occurs in goats, making pituitary neoplasia an important differential diagnosis for goats with unexplained udder enlargement. Udder enlargement was also a key clinical finding in goats with mammary neoplasia with a wide range from 0.5 to 240 months. Of the 10 goats in the mammary neoplasia group, 5 had a history of treatment for suspected mastitis at 1 point prior to admission to the veterinary teaching hospital. This data demonstrates the need for milk cultures to definitively diagnose mastitis as well as the need for further diagnostics in the event of a negative culture or unresponsive treatment. Neoplasia should be considered a differential in goats with udder enlargement.

Within the group of goats diagnosed with thoracic neoplasia, the most common neoplasm was a thymoma. The majority (3/4 [75%]) of mediastinal thymoma neoplasms were considered incidental findings as they did not have associated clinical signs and were found coincidentally on radiographs or necropsy. Reported clinical signs associated with mediastinal thymomas appear to be variable as one report⁶ found that goats with mediastinal masses displayed evidence of respiratory distress or marked tachypnea while another² reported that no clinical signs could be attributed to thymomas in dairy goats. Neoplasms that are found incidentally or do not appear to negatively affect a goat’s health may go undiagnosed due to the risk and cost of pursuing invasive diagnostics. As a result, the incidence of mediastinal thymomas may be higher than what was reported in the present study. In contrast, goats with ventral cervical thymomas presented most commonly for a visible mass. The majority of these goats underwent surgical excision without complications. Resecting these masses is important because clinical signs associated with compression of adjacent structures include respiratory signs or megaesophagus.¹⁶ Resection of suspected ventral cervical thymomas prior to definitive diagnosis may be an appropriate treatment in some cases because diagnosis with minimally invasive techniques like FNA can be challenging.¹⁷ In 6 of 9 of the goats diagnosed with thymomas, the initial attempt at mass diagnosis was FNA and cytology. Of these 6 goats, FNA was nondiagnostic in 3 (50%). The large number of proliferating lymphoid cells in thymomas make diagnosis by FNA challenging. The small number of cells evaluated by cytology is often insufficient to definitively differentiate a thymoma from other structures or masses, such as lymph nodes and lymphoma. Biopsy for histopathology, while more invasive and costly, could increase the likelihood of obtaining a diagnosis in goats with suspected thymoma.

The overall prevalence of metastasis in the present study population was low (4/58 [7%]). The tumors with confirmed metastasis were mammary sarcoma with metastasis to the lungs, mediastinal carcinoma with metastasis to the lungs and mesentery, hepatic melanoma with metastasis to the spleen and kidney, and hepatic adenocarcinoma with metastasis to the lungs and mesenteric lymph nodes. In contrast to other species such as dogs¹⁸ and humans,¹⁹ there was no evidence of metastasis in any of the goats diagnosed with mammary carcinoma. Follow-up data were available for 5 of 8 goats that underwent surgical mastectomy for known or suspected mammary neoplasia. None of the goats that underwent mastectomy showed evidence of metastasis or regrowth on follow-up (range, 5 months to 4 years), suggesting that complete mastectomy may be curative if no metastasis is present at the time of surgery. Surgical mastectomy with small, noninvasive tumors is known to be an effective treatment in dogs.²⁰ Mastectomy should be considered as a treatment option for pet goats with mammary neoplasia in which raising kids and producing milk are less important to owners than longevity and quality of life. It should be noted, however, that not all goats in the present study had additional diagnostics performed to evaluate for metastasis, diagnostics performed were mainly limited to thoracic radiographs, and metastasis may have occurred in goats after initial tumor diagnosis. Thus, the rate of metastasis may be higher than what was reported in the present study.

In the US, goats are legally considered a food-animal species regardless of their intended purpose (pet vs production animal). Therefore, any extralabel drug use in goats must satisfy the requirements for such use under the AMDUCA of 1994. Many medications (eg, piroxicam) that were identified in the medical records as having been given to goats in this study were not FDA approved for use in goats. In these cases, an official request should have been submitted to the Food Animal Residue Avoidance Databank for determination of an appropriate withdrawal interval. Due to the limited number of drugs approved for use in goats, responsible and legal extralabel drug use is therefore likely to continue to constitute an important means of treating goats with a wide range of diseases, including neoplastic conditions. There is no clear guidance regarding the use of radiation therapy under AMDUCA. Use of traditional chemotherapeutic agents was not identified in the medical records of the goats in the present study. Under the tenets of AMDUCA, a veterinarian must be able to ensure that administration of the drug to a food animal would not pose a public health risk and furthermore that a suitable withdrawal period can be established. Lack of data regarding legal, safe, and efficacious use of chemotherapeutics in goats is a major hurdle to incorporating these drugs into clinical practice. Laws regarding use of extralabel drugs, chemotherapeutics, and radiation therapy may differ in other countries.

The primary limitations of this study were the retrospective nature and small number of goats diagnosed with each type of neoplasia. Drawing conclusions about treatment and progress must be done with caution. Further studies are needed to prospectively investigate treatment and outcome in goats with neoplasia and identify risk factors to improve early diagnosis. In the mean time, it is important to emphasize to pet-goat owners the importance of early evaluation and close monitoring for clinical signs that could indicate neoplasia.