Abstract
A 12-year-old, neutered male, mixed-breed, domestic cat was presented for dysuria and haematuria accompanied by recurrent dyschezia and constipation. At rectal digital examination a non-painful, globose and relatively immobile mass was detected at the pelvic brim, ventral to the rectum. Abdominal ultrasound showed the prostate replaced by a mass with a regular shape but patchy/non-uniform echogenicity. A prostatectomy followed by prepubic urethrostomy was performed. At histopathology the tumour was composed of epithelial ducts and acini with malignant features, surrounded by proliferating cellular stroma with mitoses and nuclear atypia; an immunohistochemical panel confirmed the biphasic nature of the tumour proliferation. The diagnosis was non-infiltrating malignant mixed tumour, resembling human sarcomatoid carcinoma of the prostate. Two years after surgery the animal has not shown any health problems. To the author's knowledge, this is the first reported case of prostatic tumour with a positive follow-up after surgical treatment in cat.
A 12-year-old, neutered male, mixed-breed domestic cat was referred with a 3-week history of dysuria and haematuria, accompanied by recurrent dyschezia and constipation, which were unsuccessfully treated by the referring veterinarian with antibiotic and urinary acidification. On physical examination, abdominal palpation revealed distension of the urinary bladder and large intestine; the bladder presented high repletion degree and was tense while the large intestine presented soft, doughy faecal contents. Rectal digital examination demonstrated a firm, globose and non-painful mass ventral to the rectum, at the pelvic brim. Complete blood count and serum biochemistry were within normal ranges and feline leukaemia virus-feline immunodeficiency virus serology by Enzyme-Linked Immunosorbent Assay (ELISA) (Snap Combo Plus FIV-FeLV) was negative. Urine was collected by cystocentesis and urinalysis revealed numerous low urinary tract epithelial cells and occasional red and white blood cells; bacterial culture was negative.
Abdominal ultrasound was performed with the cat in right lateral recumbency, using a 7.5–10 MHz sector transducer. Once the bladder was identified, the urethra was followed caudally until the pelvic inlet. At the anatomical site of prostate gland a globoid mass 2 cm in diameter, surrounding the urethra, was evident. The globoid mass had well defined margins and a heterogeneous echotexture and echogenicity, and apparently replaced the normal prostate (Fig 1a and b). The medial iliac lymph nodes were not enlarged and had homogeneous parenchyma with normal echogenicity. The bladder neck and the urethral tract cranial to the prostatic mass were distended by urine. Other abdominal structures had a normal ultrasonographic appearance in terms of echogenicity, shape, dimension and anatomical position. Echo-guided trans-abdominal fine needle aspiration was performed from the mass, using 22 g×11/4″ needles, and smears were stained with the Wright method. Microscopically, the samples were scarcely cellular and displayed a twofold population of moderately pleomorphic epithelial and spindle cells. Both types of cells presented indistinct cytoplasmic borders and high nucleus/cytoplasma ratio. Findings were regarded as consistent with a presumptive diagnosis of malignant prostatic tumour.
Fig. 1.
Prostatic sarcomatoid carcinoma in a neutered cat. (a) Ultrasonographic sagittal image. The prostate appears enlarged, with a globoid shape and a heterogeneous echotexture. Hyperechoic foci and anechoic to hypoechoic cystlike structure are present. (b) Ultrasonographic transverse image. The gland (arrows) shows a hyperechoic aspect and a heterogeneous echotexture; a globoid shape with well defined margination is evident. The hypoechoic area within the central part is the urethra. (c) Barium enema examination, lateral radiograph. Note the rectum dorsal displacement with a filling defect caused by a partial lumen obstruction at the point of contact with the enlarged prostate. (d) Transverse section of prostate after surgical removal. The blue area in the centre of the gland is an urinary catheter inserted in urethra and stained with a methylene blue solution.
Lateral and ventro-dorsal radiographs of the pelvic area following barium enema demonstrated lumen narrowing and dorsal displacement of the distal colon rectum, which was pushed toward sacrococcygeal vertebrae by the prostatic mass (Fig 1c). A retrograde contrast urethrocystogram revealed both a normal shaped, replete and positioned bladder and urethra. The prostate shadow was not diagnostic. Moreover, thoracic radiographs in standard projections (right and left lateral, and ventrodorsal) were performed in order to verify the absence of pulmonary metastasis.
Following tumour staging and given the absence of metastatic disease and the good body condition, a complete prostatectomy was recommended. Pre-anaesthesia the cat was treated with acepromazine 1 mg/kgIM (Prequillan; Fatro SpA). Anaesthesia was induced with ketamine 20 mg/kgIM (Ketavet 100; Farmaceutici Gellini) and acepromazine 0.04 mg/kgIM (Prequillan; Fatro SpA), and maintained by 1.5–2% isoflurane (Isoflo; Esteve Farma Lda) in oxygen through a 3 mm endotracheal tube (veterinary straight endotracheal tube; Cook). Analgesia was achieved by IV administration of buprenorfine 0.01 mg/kg every 6 h (Temgesic; Schering-Plough). The cat was positioned in dorsal recumbency, and the abdomen was prepared for aseptic laparotomy. After catheterisation of the urethra (Protex Jackson cat catheter 3F 1.00 mm OD×11.0 cm), the abdomen was incised on the ventral midline from the umbilicus to the pelvic inlet, and the prostatic mass exposed by careful dissection through the periprostatic fat. A mass 3 cm in diameter was exposed and this appeared well circumscribed, symmetrical, globoid, regular in outline and very firm in texture. Regional lymph nodes, bladder and periprostatic tissues did not show any changes, and there were no adhesions between the prostatic mass and the surrounding omentum. Blood vessels supplying the prostate and the vasa deferentia were individually ligated and divided close to the gland. The urethra was dissected cranial and caudal to the prostatic mass, which was removed and fixed in 10% neutral buffered formalin. A prepubic urethrostomy was created on the ventral midline by suturing the dissected urethra to the surrounding skin with simple interrupted sutures using 4/0 glyconate monofilament (Monosyn; Aesculap). The abdominal wall and subcutaneous tissues were closed routinely. Antibiotic treatment with amoxicillin 15 mg/kg SC every 48 h (Neo Vet-Cillin LA; Ceva Vetem SpA) was initiated postoperatively for 7 days. An Elizabethan collar was used to prevent the cat from licking the suture area.
The resected specimen was a 3 cm in diameter firm and whitish spheroidal mass, which on sectioning consisted of a whitish irregularly lobulated tissue; the urethra appeared centrally placed (Fig 1d). The sample was fixed in formalin and routinely processed for histology. Haematoxylin and eosin stained sections revealed throughout the sample the expansive growth of a tumour tissue composed of two patterns of densely proliferating epithelial and stromal cells (Fig 2). Epithelial cells were arranged in acini and tubules composed of polygonal epithelial cells, with round to oval nuclei, prominent nucleoli, and scant eosinophilic cytoplasm; mitoses were one to three per high power field. These glandular islands were surrounded by abundant mesenchymal tissue, composed of haphazardly arranged pleomorphic spindle cells, with sparse areas of myxoid and chondroid differentiation; mitotic figures were rarely seen. Isolated lipocytes were occasionally visible. Tumour cells appeared almost all viable, without degeneration and necrosis; sparse stromal infiltrations of lymphocytes and macrophages were also noted. The capsule was not infiltrated and vascular invasion was not noted. Normal prostatic gland tissue was not evident. Immunohistochemistry was performed using a modified avidin-biotin peroxidase complex (ABC) method (LSAB Kit, Dako, Glostrup, Denmark) according to the manufacturer's instructions with the following commercial antibodies: AE1/AE3 cytokeratins (diluted 1 in 50, Dako), cytokeratin 5/6 (diluted 1 in 100, Zymed, San Francisco, CA), cytokeratin 14 (diluted 1 in 300, Neomarkers, Fremont, CA), cytokeratin 19 (diluted 1 in 50, Dako), vimentin (diluted 1 in 100, Dako), S-100 protein (diluted 1 in 1600, Dako), desmin (diluted 1 in 50, Dako), α-smooth muscle actin (diluted 1 in 100, Dako) and factor VIII-related antigen (diluted 1 in 1500, Dako). Suitable positive controls were added (normal feline epidermis for cytokeratins and vimentin; normal feline lymph node for S-100 protein; normal feline intestine for desmin, α-smooth muscle actin and factor VIII-related antigen). As negative control, isotype matched irrelevant antibodies (NeoMarkers) were used in replicate sections instead of primary antibodies.
Fig. 2.
Sarcomatoid carcinoma in a cat. (a) The tumour is composed by large islands of epithelial cells arranged in acini and tubules and is surrounded by abundant mesenchymal tissue. Haematoxylin and eosin, 100×. (b) Epithelial cells are characterised by moderate amount of eosinophilic cytoplasm, indistinct borders, round to oval nuclei and prominent nucleoli; mitoses are also evident. Haematoxylin and eosin, 400×. (c) The mesenchymal component of the tumour is composed of haphazardly arranged pleomorphic spindle cells, with area of myxoid differentiation. Haematoxylin and eosin, 400×.
Epithelial cells displayed a diffuse strong cytoplasmic expression of AE1/AE3, 5/6 and 19 cytokeratins, and stained negatively for the other markers. The stromal cells stained diffusely for vimentin and S-100 protein and focally for α-smooth muscle actin. Factor VIII-related antigen was only expressed in endothelial cells.
The diagnosis was low grade non-infiltrating malignant mixed tumour. Immunohistochemistry confirmed the biphasic nature of the tumour proliferation and suggested the myoepithelial origin of part of the stromal component.
Recovery from anaesthesia was uneventful and the follow-up was without complications. At the examination 2 months postoperatively, the cat remained clinically normal but the owner reported that the cat presented sometimes mild urinary incontinence. Two years after the surgery the animal has not shown any health problems referable to metastatic disease nor local recurrence.
The feline prostate is in cats a bulb-shaped bilobated gland about 10 mm in length located dorsolaterally to the urethra, immediately caudal to the neck of the urinary bladder. 1 Prostatic diseases are uncommonly reported in cat. Literature reports of non-neoplastic disorders are limited to single cases of bacterial prostatitis, 2 periprostatic cysts, 3 hyperplasia, 4 and squamous metaplasia. 5 Neoplasms, although regarded as the most frequent prostatic diseases, 1 are also extremely rare: to the author's knowledge, only five cases of prostatic tumours have been described in the veterinary literature, all diagnosed as carcinomas or adenocarcinomas. 6–9 Furthermore, a fibroadenoma of the prostate has been reported in a 13-year-old neutered cat. 10
The epithelial-stromal figures of the tumour reported here differ from the cases of prostatic tumours already described in cats, and also in dogs, and resemble those described in tumours of the human prostate characterised by concurrent epithelial and stromal proliferation, notably phyllodes tumour and sarcomatoid carcinoma. 11
Phyllodes tumour of the prostate is characterised by prominent myxomatous and cellular stroma with tortuous elongated epithelial ducts often dilated or arranged in a ‘leaf-like’ pattern, similar to phyllodes tumour of the human breast, 11,12 and are classified as benign, borderline or malignant based on cellular atypia and the mitotic rate of proliferative cellular stroma, yet the glands have a benign morphology. 12 Sarcomatoid carcinoma (or carcinosarcoma) of the prostate is a rare type of prostate cancer that demonstrates a combination of malignant epithelial and sarcomatoid components 13 : the epithelial component of these tumours is often a high-grade adenocarcinoma, and the accompanying sarcomatoid component demonstrates a spindled appearance, although heterologous elements with osteoblastic, chondroblastic and myoblastic differentiation may be present. 11 In general, sarcomatoid carcinoma of the prostate has been described as an aggressive neoplasm with an associated poor prognosis. 13 Although the origin of these tumours has been controversial, the epithelial and stromal components are currently thought to be derived from a single cell of origin in sarcomatoid carcinoma, 14 whereas phyllodes tumour should represent a combination of separate epithelial and mesenchymal tumour types. 15
In this case, the obvious atypia in both epithelial and mesenchymal cells, the exuberant glandular proliferation and the divergent differentiation of the mesenchymal fraction support the histological diagnosis of sarcomatoid carcinoma, that in this feline case demonstrated a relatively benign behaviour, different to the highly malignant behaviour described in man.
Clinical signs referred in reported feline prostatic tumour cases are variables, the most frequent being haematuria and dysuria. 1,8,9 Indeed, the cat reported here presented pollakiuria, and urinary obstruction, but also weight loss, inappetence, lethargy and constipation due to the dorsal displacement of rectum.
All reported cases of prostatic tumours in cats were high-grade carcinomas, with documented lymph node and lung metastases, and were diagnosed post mortem or caused death shortly after the surgery. 1 Conversely, this case had a positive follow-up, which suggests that in selected cases feline prostatic tumours may be successfully treated by surgery.
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