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.     

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.     

A review of equine mucocutaneous squamous cell carcinoma

Squamous cell carcinoma (SCC) accounts for approximately 20% of all equine mucocutaneous (MC) tumours and continues to present a therapeutic challenge to practitioners. Most MC‐SCC are locally invasive and slow to metastasise, but metastasis to local lymph nodes is not uncommon. The most common location for MC‐SCC is the periorbital region, with the eyelid most commonly affected. Although only 13% of MC‐SCC involves the external genitalia, MC‐SCC is the most common neoplasm of male genitalia. Equine caballus papillomavirus‐2 has recently been linked to MC‐SCC and may prove to be necessary for tumour development. Risk factors may include chronic exposure to ultraviolet light and chronic skin irritation. Horses developing genital MC‐SCC tend to be older compared to those with periorbital MC‐SCC. Histopathology is required for definitive diagnosis of MC‐SCC, although horse phenotype and lesion location may suggest MC‐SCC. Several treatment modalities have been successful in eliminating or managing MC‐SCC, with surgical excision and intratumoural chemotherapy yielding the best results. Other treatment options including cryotherapy, hyperthermia, radiotherapy and photodynamic therapy are often used as adjunctive therapies. Early recognition of tumours and prompt intervention are associated with a positive outcome.     

Penile and preputial tumours in the horse: a retrospective study of 114 affected horses

REASONS FOR PERFORMING STUDY: Preputial and penile tumours are more common in horses than in other domestic animals, but no large surveys of male horses with tumours of the external genitalia are available. OBJECTIVE: To present a retrospective analysis of male horses with neoplasms of the external genitalia. METHODS: The penile and preputial tumours of 114 horses were evaluated. Data recorded included age, gelding or stallion and breed; type and site of lesion; involvement of regional lymph nodes; histopathology (including grading of squamous cell carcinoma); and results of radiographic examination of the thorax. RESULTS: Mean age of horses was 19.5 years with no apparent breed predilection. Common presenting clinical signs were irregularities (e.g. the presence of a mass and/or ulceration) on the integument of the penis and prepuce, and purulent or sanguineous discharge from preputial orifice. Squamous cell carcinoma (SCC) was the most prevalent neoplasm followed by papillomas and melanomas. A basal cell carcinoma, neurofibrosarcoma, adenocarcinoma or fibrosarcoma were each found on single horses. Squamous cell carcinomas with poor differentiation had a higher tendency to metastasise than did more differentiated tumours. CONCLUSIONS: Squamous cell carcinoma is the most common urogenital tumour of the male horse and occurs primarily in old horses. Horses with poorly differentiated SCCs tend to have a higher incidence of regional metastases. Pathology of lymph nodes, even when not palpably enlarged, is a valuable diagnostic exercise. Radiology of the thorax to detect lung metastases is of little value.     

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.     

Urinary bladder rupture secondary to penile and preputial squamous cell carcinoma in a gelding

Squamous cell carcinoma (SCC) is the most common external genital neoplasm. Early detection, diagnosis and treatment are paramount to successful outcome; overlooked or misdiagnosed SCC can rapidly invade tissues and metastasise, producing potentially fatal complications. This report describes a case of overlooked SCC that resulted in severe penile infiltration, urethral stricture, and subsequent urinary bladder rupture and peritonitis.     

Delayed metastasis of ocular squamous cell carcinoma following treatment in five horses

Identification of regional and/or distant metastasis following treatment and local resolution of primary ocular squamous cell carcinoma (SCC) was observed in 5 horses. In all cases, identification of metastasis occurred at least 18 months following treatment of the primary ocular lesions. In 3 cases, invasion of blood or lymphatic vessels by neoplastic cells was identified in the excisional biopsies of the primary tumour. Two horses developed SCC at 2 or more separate sites. At the time metastases were identified, there was no evidence of local recurrence of the ocular tumour in any of the horses. These cases confirm the importance of long‐term monitoring of horses for metastatic disease following treatment of ocular SCC even in the absence of local recurrence.     

Primary penile adenocarcinoma with concurrent hypercalcaemia of malignancy in a dog

A 13‐year‐old male neutered Siberian husky crossbreed dog was presented with a 3‐week history of haematuria and penile swelling. Clinical examination and computed tomography demonstrated a soft‐tissue mass located at the base of the penis without signs of other primary tumours or metastasis. Clinicopathological findings revealed paraneoplastic hypercalcaemia. Fine‐needle aspiration cytology of the mass suggested an epithelial tumour with several criteria of malignancy present. Following surgical excision of the mass, the hypercalcaemia resolved. Histopathology and immunohistochemistry revealed features consistent with an adenocarcinoma. Despite thorough examination, no perineal or anal sac tumour was found. To the authors’ knowledge, this is the first reported case of a penile adenocarcinoma with hypercalcaemia of malignancy.     

Pigmented squamous cell carcinoma of the conjunctiva of a horse

Abstract A heavily pigmented tumor was removed from the lateral, perilimbal, bulbar conjunctiva of a bay Thoroughbred horse. Excision was incomplete and the base of the tumor was lasered on the assumption that the tumor was a melanoma. No other ophthalmic lesions were seen. Histology showed the mass to be a pigmented squamous cell carcinoma (SCC). The prognosis and recommended treatment protocols are different for SCC and melanoma. This is, to the best of our knowledge, the first report of an ocular, pigmented SCC in the veterinary literature.     

Squamous cell carcinoma of the equine external genitalia: a review and assessment of penile amputation and urethrostomy as a surgical treatment

A retrospective analysis was performed on 48 cases of suspected neoplasia involving the equine external genitalia. Forty nine squamous cell carcinomata (SCC) and 23 squamous papillomata (SP) were identified. Two cases of epithelial hyperplasia and one case of habronemiasis were also recognised histopathologically. The glans penis was the most common site of tumour development accounting for 53 per cent of cases of SCC and 61 per cent of SP. The urethral diverticulum, urethral process or urethra was involved in 27.6 per cent (8/29) of cases of SCC. Twelve per cent (5/41) of cases of SCC were confirmed to have metastatic involvement of the local lymph nodes. Papillomata showing pre-malignant changes were identified in five cases. Seventy five per cent (36/48) of the animals presented were ponies. All were geldings, mean age 16.5 years. Penile amputation and urethrostomy, preputial ablation and proximal urethrostomy or local excision were used in the surgical management of these animals; three cases were inoperable and destroyed at presentation. Oedema, haemorrhage and stenosis of the urethrostomy site were encountered as post operative complications. Sixty six per cent (6/9) of animals with SCC of the glans penis (without urethral involvement), which had a known history over the follow up period, treated by penile amputation and urethrostomy survived for longer than 18 months. Similarly, of those with urethral involvement only 28.6 per cent (2/7) survived for a similar follow-up period. SCC not uncommonly affects the external genitalia of aged pony geldings and frequently the glans penis. If the lesion is identified before local metastasis occurs, penile amputation and urethrostomy is indicated and the prognosis is favourable.     

Feline head and neck squamous cell carcinoma: a natural model for the human disease and development of a mouse model

Head and neck squamous cell carcinoma (H/N SCC) is a devastating disease in humans and cats, and shares similar features between the two species. The large population of pet cats inthe United States, along with the high incidence of oral SCC in the cat, makes the cat an attractive candidate as a natural model for the human disease. There are similarities in pathology, progression, outcome, resistance to treatment, possible aetiologies and p53 expression, and we discuss the benefits of the cat as a natural model. We describe the development of a nude mouse xenograft model of feline oral SCC using the SCCF1 cell line transfected with a luciferase expression construct. In vivo tumour growth and metastasis were measured using serial bioluminescent imaging, and tumours grew best in the subcutis. The cat and nude mouse models will be useful to investigate the pathogenesis and the molecular basis of H/N SCC, and for preclinical drug screening.     

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.     

Skeletal metastasis from a squamous cell carcinoma of the nictitating membrane in a Haflinger horse

A 12-year-old Haflinger gelding with a history of a persistent cough was referred for evaluation of a severe lameness of the left forelimb. An excision of the right nictitans had been performed 2 years prior to presentation, and a squamous cell carcinoma (SCC) with embolic neoplastic cells in several blood vessels had been confirmed by histopathology. The origin of the lameness could not be localised with regional analgesia; therefore, a nuclear scintigraphic examination was performed. This revealed an area of marked increased radiopharmaceutical uptake at the level of the caudodorsal border of the left scapula. Further examination, including ultrasound-guided biopsy of the suspect region, confirmed the presence of SCC invading the scapula. Due to poor a prognosis, the horse was subjected to euthanasia. Prior to euthanasia, the gelding was tested homozygous for the missense variant in the damage-specific DNA-binding protein 2 (DDB2) gene, which is reported as a risk factor for the development of nictitans SCC in Haflinger horses. Post-mortem evaluation revealed multiple SCC metastasis, affecting the scapula, the liver and the lungs. To the authors' knowledge, this is the first reported case of bone metastasis following a primary periocular SCC in a horse.     

Interstitial brachytherapy in the management of haemangiosarcoma of the rostrum of the horse: Case report and review of the literature

Sarcomas arising in the equine species are rare tumours, and treatment is generally surgical. Radiotherapy has been used in the management of malignancies of large animals; however, conventional external radiotherapy delivery is difficult. Interstitial brachytherapy has been used in the management of human sarcomas with reasonable success, although equine experience is minimal. We report a case of equine haemangiosarcoma treated with brachytherapy demonstrating the feasibility of the procedure and the highly malignant natural history of haemangiosarcoma. An 8‐year‐old American Saddlebred gelding presented for evaluation of a soft tissue mass on the forehead which had been present for at least 6 months. Initial surgical attempts at management were unsuccessful; therefore a radiation oncologist specialising in brachytherapy was consulted. The radiation oncologist and veterinary surgeon performed an interstitial implant of the tumour mass on the rostrum of the horse under general anaesthesia. The procedure was well tolerated by the horse. The tumour demonstrated immediate response and was noted to have completely regressed within 6 weeks of the implant removal. Unfortunately, the horse developed widespread metastatic disease and required euthanasia. At the time of necropsy, no visible tumour was identified at the implant site. Interstitial brachytherapy is feasible in soft tissue sarcomas of the horse; however, supportive demands are great with this procedure and we recommend it only be done at large speciality centres.     

Alternative method to facilitate resolution of paraphimosis after penile trauma in the horse

Inflammation associated with traumatic injury to the penis is characterised by pain, heat and oedema. Ensuing penile swelling interferes with retraction of the penis into the prepuce, resulting in paraphimosis. This report describes the use of a 5 l capacity pressure infusion bag to reduce penile oedema in three horses. This technique provided complete resolution of oedema and associated paraphimosis in approximately 1 h. The use of the bag, along with an abdominoinguinal bandage, a plastic funnel suspensory device, or a penile repulsion device (Probang) to avoid recurrence, offers a novel treatment that may be performed with the horse sedated.     

Multimodal therapeutic approach and interdisciplinary challenge for the treatment of unresectable head and neck squamous cell carcinoma in six cats: a pilot study

Feline head and neck squamous cell carcinoma (SCC) is a loco‐regional disease harbouring a poor prognosis. The complex anatomic location precludes aggressive surgical resection and tumours recur within weeks to few months. Response to chemotherapy and local control after radiation therapy has been disappointing. In this study, a multimodal approach including medical treatment (thalidomide, piroxicam and bleomycin), radiation therapy (accelerated, hypofractionated protocol) and surgery was attempted in six cats. Treatment was well tolerated. Three cats with sublingual SCC were alive and in complete remission at data analysis closure after 759, 458 and 362 days. One cat with laryngeal SCC died of renal lymphoma after 51 days and the other with maxillary SCC died of a primary lung tumour 82 days after diagnosis. In both cats, the SCC was in complete remission. Only one cat developed metastases after 144 days. These encouraging preliminary results merit further evaluation in future trials.     

Canine osteosarcoma of the penile bone

A 13-year-old mixed breed dog was presented with difficulties to urinate, blood in the urine and a nodule at the root of the penis. The penis was completely resected, and an osteosarcoma of the penile bone was diagnosed. Radiographically, there was no evidence to suggest tumours in other bones or distant metastases. The dog was euthanized as a consequence of tumour recurrence after 2 months. This is believed to be the first reported case of a primary osteosarcoma of the penile bone.     

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.     

Mandibular squamous cell carcinoma in a 5‐year‐old Tennessee Walking Horse

Squamous cell carcinoma (SCC) is the second most common neoplasm reported in the horse, but occurs rarely in the oral cavity. Clinical signs may be insidious in onset and mimic other non‐neoplastic processes, thus delaying appropriate treatment. Timely evaluation and advanced diagnostic imaging may offer the opportunity to initiate definitive treatment. This report describes a young gelding with mandibular SCC that was evaluated for mandibular swelling failing to respond to symptomatic therapy.     

Metastatic mast cell tumour in a dog presenting with spinal pain

The clinical, advanced imaging and surgical features of a case of canine extradural mast cell tumour are presented. This rare location has only been reported once before as a primary lesion, although the present case may be a metastatic lesion. Given the frequent occurrence and treatment of cutaneous mast cell tumours in dogs, the finding of spinal metastasis is an important reminder to consider metastatic neoplasia in cases of previously treated cancers presenting with spinal pain.