Metastasis or delayed local extension of ocular squamous cell carcinoma in four horses

Four horses treated for ocular squamous cell carcinoma (SCC) that subsequently developed local tumour extension or local metastases without ocular recurrence are included in this study. Medical records were examined and long‐term follow‐up obtained through contact with owners and referring veterinarians. In 2 horses, SCC developed in the nasolacrimal duct and maxillary sinus one and 3.5 years, respectively, after treatment for SCC in the medial canthus of the eye. No recurrence of the SCC was noted in the ocular structures. Both were treated successfully with surgery and radiation therapy. Two additional horses had delayed metastasis of SCC to the parotid lymph node one and 2 years after excision of the ipsilateral third eyelid for SCC. No recurrence of the SCC was noted in the ocular structures. One was treated with surgery and radiation without success and one was not treated. Ocular SCC can spread to local tissues or lymph nodes without recurrence in the eye. The clinical manifestation of tumour recurrence may be delayed. Delayed local extension or local metastasis in horses after ocular SCC without recurrence in the eye itself has not been previously reported. Clinical signs of ocular squamous cell carcinoma should prompt immediate treatment and local recurrence despite successful treatment of the ocular disease is a possibility.     

Penile and preputial squamous cell carcinoma in the horse: a retrospective study of treatment of 77 affected horses

Reasons for performing study: The most common penile and preputial neoplasm in the horse is the squamous cell carcinoma (SCC), but no large surveys of treatment and effects of the grade of the tumour, based on the degree of differentiation, on outcome of affected horses are available. Objectives: Analysis of treatment of male horses affected with SCC of the external genitalia and long‐term results of treatment. Methods: Seventy‐seven cases of SCC were evaluated. Data recorded included treatment, outcome, post operative histopathology and retrospective tumour grading. Results: Treatments included: cryosurgery, excision, partial phallectomy, partial phallectomy and sheath ablation, and en bloc penile and preputial resection with penile retroversion and removal of inguinal lymph nodes. The incidence of recurrence after partial phallectomy was 25.6% (10/39) and following incomplete removal was 17.9% (7/39). The incidence of recurrence after en bloc resection with retroversion was 12.5% (1/8). In horses with confirmed inguinal lymph node metastasis, the incidence of recurrence was 25.0% (1/4). Poorly differentiated SCCs were more likely to metastasise than well differentiated SCCs, and there was a greater chance that the treatment would be unsuccessful. The success of treatment, complete removal and in preventing recurrence of the tumour, of male horses with SCC of the external genitalia was 55.7%. Conclusions: Horses that receive only partial phallectomy for treatment for SCC of the external genitalia have a high incidence of recurrence in contrast to horses that receive an en bloc resection. Tumour grading of SCC can help predict prognosis and guide selection of treatment.     

Prognostic factors and survival of horses with ocular/adnexal squamous cell carcinoma: 147 cases (1978-1988)

Between January 1978 and December 1988, 147 horses with ocular/adnexal squamous cell carcinoma (SCC) were admitted to the Colorado State University Veterinary Teaching Hospital (CSU-VTH). Diagnosis was confirmed by histologic examination of appropriate tissue specimens. Medical records and communication with owners, referring veterinarians, or both provided information regarding initial examination, treatment at the CSU-VTH, and final outcome. At initial examination, 123 (83.7%) horses had unilateral involvement and 24 (16.3%) horses had bilateral involvement. The nictitating membrane, nasal canthus, or both (28.1%); limbus (27.5%); and eyelid (22.8%) were most commonly affected. In addition to the ocular/adnexal location, SCC was found elsewhere in 14 (9.5%) horses at initial examination. Adequate follow-up (greater than or equal to 4 months) for examination of tumor recurrence and survival analysis was obtained for 125 (85.0%) cases. After treatment at the CSU-VTH, tumor recurred in 30.4% of the cases. Tumor location, multiple vs single tumors at initial diagnosis, and CSU-VTH treatment modality influenced the recurrence of tumors. Survival analysis revealed a good prognosis for horses with ocular/adnexal SCC. Although undefined, a conservative estimate of the median survival time was 47 months. Six factors (treatment prior to referral, tumor location, tumor size, single or multiple tumors, treatment modality at the CSU-VTH, and recurrence or nonrecurrence) were analyzed to determine their relation with survival. Treatment prior to referral, multiple vs single tumors at initial examination, and treatment modality used at the CSU-VTH did not influence survival. Tumor location influenced survival; SCC involving the eyelid or orbit was associated with the poorest prognosis. Tumor stage (maximal dimension) was inversely related with survival.(ABSTRACT TRUNCATED AT 250 WORDS)     

Factors influencing morbidity and outcome of equine ocular squamous cell carcinoma

A retrospective review of 41 cases of equine ocular squamous cell carcinoma with follow up information for 33 horses is presented. An apparent prevalence in heavy horse breeds was identified. Age and sex distribution were similar to those previously reported. High recurrence (42.4 per cent) and low metastasis (6 per cent) rates were seen. Initial tumour location, primary treatment used, or patient case history had no apparent influence on final outcome. The willingness of owners to pursue with continuous treatment correlated with a high degree of success.     

Effects of treatment with and without adjuvant radiation therapy on recurrence of ocular and adnexal squamous cell carcinoma in horses: 157 cases (1985-2002)

OBJECTIVE: To determine the effects of treatment with and without adjuvant radiation therapy on recurrence of ocular and adnexal squamous cell carcinoma (SCC) at specific anatomic locations in horses. DESIGN: Retrospective study. ANIMALS: 91 horses. PROCEDURES: Medical records of horses with histologically confirmed ocular and adnexal SCC evaluated from 1985 to 2002 were reviewed. Sex, breed, age, type of treatment, location, and recurrence of SCC were recorded. Two treatment groups determined by recurrence of SCCs treated with and without adjuvant radiation therapy were established. RESULTS: The anatomic site with the highest recurrence rate was the limbus (junction of the cornea and sclera) or bulbar conjunctiva (477%), independent of treatment group. There was a significant difference in recurrence rates of ocular and adnexal SCCs between the 2 treatment groups, independent of anatomic location. Recurrence rates of SCCs treated with and without adjuvant radiation therapy were 11.9% and 44.1%, respectively. Recurrence rates for SCCs of the eyelid, limbus or bulbar conjunctiva, and cornea treated with adjuvant radiation therapy were significantly different from those for SCCs treated without adjuvant radiation therapy. The most frequently represented anatomic site for ocular and adnexal SCCs was the eyelid (28.7%). Coat color, breed, and the interaction of age and breed had a significant effect on tumor recurrence regardless of treatment type and anatomic location. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that ocular and adnexal SCCs treated with adjuvant radiation therapy had a significantly lower recurrence rate, compared with SCCs treated without adjuvant radiation therapy, independent of anatomic location.     

Amniotic membrane transplantation for corneal surface reconstruction after excision of corneolimbal squamous cell carcinomas in nine horses

OBJECTIVE: The purpose of this study was to evaluate the usefulness and effectiveness of permanent amniotic membrane transplantation as an adjunctive treatment to superficial keratectomy alone or combined with strontium-90 irradiation for treatment of equine corneolimbal squamous cell carcinoma (SCC) to decrease corneal scarring and recurrence rate. STUDY: The retrospective case study included 11 horses (n = 12 eyes) diagnosed and treated for ocular SCC that involved the limbus and cornea. Nine of those horses (n = 9 eyes) were treated between 2002 and 2006, with superficial lamellar keratectomy alone or combined with strontium-90 irradiation and followed by placement of a permanent amniotic membrane graft in the surgical defect. The level of scarring (i.e. the clarity of the cornea) resulting with the use of amniotic membrane was subjectively compared to cases where a permanent bulbar conjunctival graft was performed following keratectomy combined with strontium-90 irradiation or cryotherapy (n = 3 eyes). Recurrence was defined as the postoperative and postirradiation regrowth of SCC in the same site and globe. RESULTS: The nine horses that received an amniotic membrane graft after keratectomy alone or combined with irradiation showed a minimal level of scarring in a cornea that regained a greater transparency in comparison to the horses that were treated with a bulbar conjunctival graft. All of the horses that received an amniotic membrane graft had 226 +/- 218 days of follow-up without tumor recurrence (mean +/- SD), ranging from 21 days to 778 days. CONCLUSIONS: The combination of superficial keratectomy alone or associated with beta-irradiation and permanent amniotic membrane transplantation is an effective treatment of corneal or corneolimbal SCC in horses. The placement of an amniotic membrane material represents an alternative surgical procedure to bulbar conjunctival grafts, especially if there is a lack of bulbar conjunctiva tissue available after tumor resection or if a particularly large corneal resection is necessary. The amniotic membrane is incorporated into the corneal defect and seems to create noticeably much less scarring than a corneal defect covered by bulbar conjunctiva.     

Combined keratectomy, strontium-90 irradiation and permanent bulbar conjunctival grafts for corneolimbal squamous cell carcinomas in horses (1990-2002): 38 horses

OBJECTIVE: The purpose of this study was to evaluate the effectiveness of postoperative beta-irradiation with strontium-90 as an adjunctive treatment to superficial keratectomy and permanent bulbar conjunctival graft for removal of equine corneolimbal squamous cell carcinoma (SCC), in decreasing recurrence rate. STUDY: The retrospective case study included 38 horses diagnosed and treated for SCC of the eye that involved the limbus and/or cornea. The patients were treated between 1990 and 2002, with strontium-90 irradiation immediately after corneal and conjunctival graft surgery. Recurrence was defined as the postoperative and postirradiation regrowth of SCC in the same site and globe that was previously treated. RESULTS: The Appaloosa was the most commonly represented breed and horses that had more than one base coat color represented the majority of the cases (53%). The coat colors of white, chestnut/sorrel and gray were the most commonly represented colors of the horses treated. Eight horses (21%) could not be assessed for tumor recurrence due to lack of two or more post-treatment examinations, and another horse was enucleated 6 days postoperatively due to progressive corneal ulceration. Twenty-four horses (63% of the entire study population; 83% of the followed cases) had a mean +/- SD of 1754 +/- 1319 days without tumor recurrence, ranging from 14 days to 5110 days. Five horses (13% of the entire study population; 17% of the assessed horses) had tumor recurrence at a mean +/- SD of 449 +/- 339 days with a range of 29 days to 900 days. For the five recurrences, treatment included local excision (n = 1), enucleation (n = 2), and additional strontium-90 therapy (n = 3). CONCLUSIONS: The combination of superficial keratectomy, beta-irradiation and permanent bulbar conjunctival grafts for limbal, corneal or corneolimbal SCC in horses is effective in at least 83% of the horses. Recurrence occurred in about 17% of the horses. Multiple biannual re-examinations are recommended to observe for tumor recurrence.     

Challenges in the treatment of equine periocular squamous cell carcinoma

Management of periocular squamous cell carcinoma is challenging because of the need for adjunctive therapy, the adverse effects of therapies and the frequent recurrence of SCC. Appropriate treatment of equine ocular SCC usually involves surgical excision combined with adjunctive therapy selected as appropriate for the anatomic site of the lesion. Metastasis of periocular SCC has been reported to occur in approximately 6–15% of cases. The horse owner should be carefully educated to understand that for best long‐term results from the treatment of periocular SCC, they must be diligent in observing signs of recurrence or metastasis and be willing to have the horse examined as soon as adverse signs are observed. Furthermore, external beam radiation may be effective in the treatment of metastatic SCC and further clinical studies of this treatment modality are needed.     

Carbon dioxide laser photoablation adjunctive therapy following superficial lamellar keratectomy and bulbar conjunctivectomy for the treatment of corneolimbal squamous cell carcinoma in horses: a review of 24 cases

Objective To determine the complications and nonrecurrence rates following superficial lamellar keratectomy, bulbar conjunctivectomy, and adjunctive carbon dioxide (CO₂) photoablation for corneolimbal squamous cell carcinoma (SCC) in the horse. Study design Retrospective study. Sample population Twenty‐four horses with corneolimbal SCC. Procedure Medical records of horses diagnosed with corneolimbal SCC that was surgically excised and where CO₂ photoablation was used as an adjunctive therapy from 2000 to 2007 were reviewed. Signalment, prior therapy, tumor location and size, complications, and recurrence of SCC were recorded. Results The Thoroughbred was the most commonly (25%) represented breed. Lesions were >10 mm in diameter in 70.8% of cases. Eight horses (33.3%) had neoplastic cells extending to the deep margin of the keratectomy. All horses were available for follow‐up for an average ± standard deviation of 40.7 ± 25 months. Four horses (16.7%) developed a recurrence of SCC. Three of these four horses underwent repeat keratectomy and CO₂ photoablation, one each, at 4 months, 1, and 2 years following the initial procedure. One horse underwent enucleation 8 months following the initial procedure. Conclusions and clinical relevance As an adjunctive therapy, CO₂ photoablation was successful in 87.5% of the horses following a single procedure and in a total of 91.7% following a second therapeutic application. CO₂ photoablation appears to be effective as an adjunctive therapy following removal of large corneolimbal SCC in the horse and in cases in which all tumor cells were not excised.     

Penile and preputial tumours in the horse: literature review and proposal of a standardised approach

Penile and preputial tumours are not uncommon in the horse, but can cause discomfort and lead to serious complications. Several types of tumour of the male external genitalia have been described. The most common type is the squamous cell carcinoma (SCC), which is found mainly in older horses. Reports of a breed predilection for penile tumour formation are equivocal, but castration, coat colour, poor hygiene and various infectious agents have all been suggested to predispose to the development of some types of tumour (e.g. SCC, papilloma and melanoma). Careful assessment of the primary tumour is an important first step in the design of an optimal treatment protocol. Invasiveness, differentiation grade, tumour size and presence of metastases are all relevant to the decision to pursue additional diagnostic procedures or specific treatment options. To date, no standard protocol has been reported for the approach to penile tumours in the horse and treatments range from minimally invasive therapies (e.g. topical use of 5-fluorouracil) to radical surgical interventions (e.g. en bloc penile and preputial resection with penile retroversion). Completeness of removal of the neoplasm and therefore risk of recurrence is highly dependent on the type of therapy chosen. However, the size and histopathological features of the primary tumour are also important factors with respect to the likelihood of recurrence. This review describes the most common penile and preputial neoplasms in the horse, and outlines a standard protocol aimed at arriving at a specific diagnosis and tailoring the therapeutic approach accordingly.     

Prevalence of ophthalmic disease in blue‐eyed horses

A perception exists amongst referring veterinarians and the lay public that blue‐eyed horses have increased frequency of ocular disease. The aim of this retrospective study was to assess the prevalence of ocular disease in horses with blue or heterochromic eyes relative to those with brown eyes. The medical records of horses presenting to either the Comparative Ophthalmology services or Equine Medicine/Surgery services at 2 institutions were reviewed. Signalment, ocular and nonocular diagnoses were recorded. Ocular disease was divided into 4 categories: adnexa, cornea, intraocular/orbit and squamous cell carcinoma (SCC). Owners were contacted by telephone to confirm iris colour. Chi‐square analysis was used to compare group proportions. A total of 164 eyes of horses with ocular disease and 212 eyes of horses without ocular disease were included. Blue eyes were equally common in the ocular disease and nonocular disease groups (P = 0.265). There was no significant difference in the proportion of blue‐ and brown‐eyed horses when comparing the adnexal and corneal (P = 0.548), corneal and intraocular/orbit (P = 0.379) and adnexal and intraocular/orbit (P = 0.843) categories. A significant difference was detected in the proportion of blue‐eyed horses between the adnexal (P = 0.000), corneal (P = 0.033), intraocular/orbital (P = 0.000) and SCC categories, with a higher proportion of blue‐eyed horses in the SCC than in the other 3 groups. Horses with blue or heterochromic irides are more likely to develop ocular SCC than horses with brown irides, but are not more likely to have adnexal, corneal or intraocular/orbital disease or to be presented for evaluation of ophthalmic disease. Veterinarians should consider the results of this study when answering questions from the lay public regarding the predisposition of blue‐eyed horses to ocular disease.     

A retrospective comparison of surgical removal and subsequent CO2 laser ablation versus topical administration of mitomycin C as therapy for equine corneolimbal squamous cell carcinoma

Objective To compare the complications and nonrecurrence rate following topical mitomycin C (MMC) therapy vs. CO₂ laser ablation for treating equine corneolimbal squamous cell carcinoma (SCC). Study design Retrospective study. Sample population Twenty‐five horses with corneolimbal SCC. Procedures Medical records of horses undergoing surgical tumor resection followed by either topical MMC therapy (0.04%) or CO₂ laser ablation between the years of 2004 and 2010 were reviewed. Recurrence and complications were compared between groups and within MMC subgroups defined by the time at which treatment was initiated relative to surgery. Results Therapy with topical MMC resulted in a nonrecurrence rate comparable to that achieved with CO₂ laser ablation (82.4% vs. 85.7%, respectively). Initiation of MMC following epithelialization of the surgical site a mean of 15 days postoperatively did not result in increased recurrence rates relative to treatment in the immediate postoperative period. Vision‐ or globe‐threatening complications tended to occur with greater frequency in horses receiving topical MMC in the immediate postoperative period (5 of 6 major complications) relative to following epithelialization of the surgical site (1 of 6 major complications). Conclusions Horses receiving adjunctive topical MMC therapy were no more likely to experience tumor recurrence than were horses undergoing CO₂ laser ablation in the horses in this study. Initiation of two to three rounds of MMC following epithelialization of the surgical site results in fewer major complications and achieves comparable disease resolution relative to treatment in the immediate postoperative period.     

Immunohistochemical evaluation of cyclooxygenase expression in corneal squamous cell carcinoma in horses

OBJECTIVE: To evaluate expression of cyclooxygenase (COX)-1 and COX-2 in the cornea, eyelid, and third eyelid of healthy horses and those affected with squamous cell carcinoma (SCC) by use of immunohistochemical techniques. ANIMALS: 15 horses with SCC involving ocular tissues and 5 unaffected control horses. PROCEDURES: SCC-affected tissues were obtained from the cornea (n = 5 horses), eyelid (5), and third eyelid (5). Site-matched control tissues were obtained from 5 horses unaffected with SCC. Tissue sections of affected and control cornea, eyelid, and third eyelid were stained immunohistochemically for COX-1 and COX-2 via standard techniques. Stain uptake was quantified by use of computer-assisted image analysis of digital photomicrographs. RESULTS: Immunoreactivity for both COX-1 and COX-2 was significantly greater in equine corneas with SCC than in control corneas. No significant differences in COX-1 or COX-2 immunoreactivity were detected in eyelid and third-eyelid SCC, compared with site-matched control tissues. CONCLUSIONS AND CLINICAL RELEVANCE: Immunoreactivity for COX-1 and COX-2 is high in equine corneal SCC, possibly indicating that COX plays a role in oncogenesis or progression of this tumor type at this site. Pharmacologic inhibition of COX may represent a useful adjunctive treatment for corneal SCC in horses.     

Metastatic synovial cell sarcoma in two cats

Synovial cell sarcoma (SCS) with metastasis to the regional lymph node was diagnosed in two cats. Synovial cell sarcomas are rare in cats and metastatic SCS has not previously been reported. In both cases, treatment consisted of limb amputation and adjuvant doxorubicin. Local tumour recurrence and pulmonary metastases were diagnosed in one cat 316 days postoperatively. This cat died of chronic renal failure 444 days after limb amputation. The second cat died of an acute pulmonary thromboembolism 41 days postoperatively without evidence of local tumour recurrence or metastatic disease.     

Calcified tumours of the paranasal sinuses in three horses

Three horses, a 10-year-old Thoroughbred mare, a 9-year-old Thoroughbred gelding and a 6-year-old Arab gelding, with calcified tumours of the paranasal sinuses, are described. All horses presented with purulent nasal discharges and facial distortion. Exophthalmos, blepharospasm and ocular discharge were also a feature in individual horses. A presumptive diagnosis of a calcified tumour was made on the basis of clinical signs and radiographic and endoscopic findings. The tumours ranged from 15 to 25 cm in diameter. A large frontonasal bone flap was used to expose the tumours, which were cleaved into several pieces with an osteotome and removed. Histological examination of the masses identified cementomas in two cases and an osteoma in the third. Long term follow up from 18 months to 5 years after surgery indicated that there was no recurrence. This case series demonstrates that, although calcified tumours of the paranasal sinuses are rare in horses, they should be considered in the differential diagnosis of purulent nasal discharge, facial swelling and ocular distortion, and are amenable to surgical treatment.     

Cyclooxygenase-2 immunoreactivity in equine ocular squamous-cell carcinoma.

Squamous-cell carcinoma (SCC) is the second most common tumor in horses, and 40%-50% may occur in ocular and adnexal structures. Cyclooxygenase (COX)-2 is an inducible enzyme responsible for the production of prostaglandins that control cell growth and the development and progression of cancer. Mechanisms responsible for the initial upregulation of COX-2 in neoplasia are unclear; prolonged sunlight exposure and mutations in the p53 gene may be possibilities. Because the etiopathogenesis of ocular SCC in horses may involve ultraviolet sunlight and p53 mutations, the purpose of this study was to characterize the immunoreactivity of COX-2 in these tumors. Cyclooxygenase-2 expression was found in 6 of 22 (27%) paraffin-embedded equine SCCs. Cyclooxygenase-2 immunoreactivity was associated with the mitotic index (P < 0.001). Strategies to inhibit COX-2 by the use of topical or systemic COX-2 inhibitors might prove to be a safe and economical treatment in some horses with SCC.     

Equus caballus papillomavirus‐2 (EcPV‐2): An infectious cause for equine genital cancer?

Reasons for performing study: The aetiology of genital squamous cell carcinoma (SCC) in horses remains unknown, but the similarity to the disease in man, for which papillomavirus infection has been shown to be a causal factor, requires to be investigated in horses. Hypothesis: One or more novel papillomaviruses cause equine genital SCC and its associated premalignant lesions. Methods: DNA was extracted from samples of equine genital SCC and performed rolling circle amplification, in order to identify closed circular DNA viral genomes within the samples. The amplified DNA was subcloned and sequenced and the DNA sequence compared to that of other papillomavirus genomes. Using PCR primers developed from these genomic DNA sequences, studies were then carried out in order to identify the frequency at which the viral DNA could be identified in equine genital cancer samples from horses in both the UK, Australia and Austria. Finally, in situ hybridisation using specific probes developed from this DNA sequence were used to confirm the presence of the viral RNA sequences in the neoplastic cells in these lesions. Results: The full length genome of a novel papillomavirus species was characterised from the equine genital SCC tissue and termed Equus caballus papillomavirus‐2 (EcPV‐2). Viral DNA and RNA was identified in the genital tumour samples, but not in the adjacent histologically normal tissue. EcPV‐2 DNA could not be identified in equine ocular or nasal carcinomas or within the scrotal skin or in most smegma samples obtained from tumour‐free horses. Sequencing of amplicons, generated from the archived equine genital tumours, identified variations within E1 and E6 on DNA and predicted protein level. Conclusions: A novel papillomavirus, EcPV‐2, is likely to play a causal role in the pathogenesis of equine genital epithelial tumours. Potential relevance: Identification of a papillomavirus causal for genital carcinomas in horses may lead to development of a vaccine that could be used to prevent this serious disease in horses. This would be analogous to man, where vaccination against oncogenic papillomavirus species is currently being used to help prevent cervical cancer.     

Tattooing of the Equine Eyelid: A Retrospective Study

In this retrospective study, medical records of 26 horses whose eyelids were tattooed were analyzed, and data regarding age, breed, eyelid pigment, eye color, sex, and reproductive status of the horses were compiled. Owners of the horses were contacted by telephone and questioned about their horses. Twenty-six horses were tattooed at Colorado State University (CSU), and one of them was tattooed twice. Records were available for 26 horses, and follow-up results by telephone were completed for 22 of those. Telephone follow-up times ranged from 3 months to 17 years after tattooing. American Paint Horses constituted 62% (16/26) of the cases, followed by Appaloosas (19% = 5/26), and Quarter Horses (8% = 2/26). In 100% (22/22) of cases, the reason for presenting the horse for a tattoo was lack of periocular pigmentation. Only two horses developed ocular or periocular squamous cell carcinoma (SCC) after their tattoos. Although the results of this study suggest that tattooing may be protective against SCC and solar blepharitis, it is by no means conclusive. However it appears to have no deleterious effects, and often owners like the appearance of the tattooed eyelid.     

Equine osteosarcoma: a series of 8 cases

In horses, osteosarcoma is a rare tumor, with the majority of reported cases occurring in the head, and, more specifically, in the mandible of young horses. The following report documents 8 cases of equine osteosarcoma, the majority occurring in male horses aged 7 years or older with a lack of metastasis identified in any horse. Six arose in the maxilla or mandible and one in the proximal tibia. The predominant subtype was fibroblastic osteosarcoma with fewer osteoblastic type tumors. All had osteoid and most had a chondromucinous matrix. Surgical excision was attempted in the majority of cases. An inability to completely excise the tumor and progressive disease typically resulted in euthanasia. To the authors' knowledge, this case series also documents the first report of an equine extraosseous osteosarcoma within the subcutaneous tissue caudal to the shoulder. Surgical excision appears successful with no recurrence of disease 14 months later. Further investigations of equine osteosarcoma and various chemotherapeutic agents are warranted to present additional treatment options.     

Equine orbital neoplasia: a review of 10 cases (1983-1998)

The clinical manifestations, laboratory findings, and survival times of 10 horses with orbital neoplasms are reported. In all cases, orbital neoplasms were malignant and locally invasive with no defined surgical circumscribed edges. It was often difficult to identify the primary cell type of the neoplasia in histologic specimens due to the poorly differentiated, anaplastic nature of the majority of cases. All except one horse were eventually euthanized 2 mo to 5 y after diagnosis due to poor response to treatment, metastasis, or unrelenting orbital neoplasia. Mean survival time increased with surgical treatment, but no significant difference was found among no treatment, chemotherapy, surgical mass removal, or exenteration/enucleation. Equine practitioners should be aware of the marked difference in prognosis of orbital neoplasms compared with ocular or localized eyelid neoplasia.