JPC SYSTEMIC PATHOLOGY

URINARY SYSTEM

December 2023

U-N04

 

Signalment (JPC #4147172-01): 12-year-old neutered male bichon frisé.

 

HISTORY: Urinary cystotomy performed approximately 10 years prior for removal of calculi. Urinary calculi recurred despite corrective diet, and a urinary bladder mass was found on ultrasound. Another cystotomy was performed to remove calculi, and the mass was excised concurrently; surgical notes stated that the mass was 3 cm, multilobulated, variably colored, and extended from the bladder mucosa into the lumen of the bladder, originating from the apex of the bladder. 

 

HISTOPATHOLOGIC DESCRIPTION:  Urinary bladder: Arising from the mildly hyperplastic urothelium, infiltrating and expanding the lamina propria and infiltrating the submucosa, and forming exophytic papillary projections is an unencapsulated, well demarcated, densely cellular neoplasm composed of polygonal epithelial cells arranged in islands and broad trabeculae on a fibrovascular stroma. Neoplastic cells have distinct cell borders, a moderate amount of eosinophilic granular cytoplasm, a round nucleus that is often vesiculate or has finely stippled or clumped chromatin and one to two distinct nucleoli. Anisocytosis and anisokaryosis are moderate and there are 8 mitotic figures per 2.37mm².  Neoplastic cells occasionally contain large, clear cytoplasmic vacuoles that occasionally contains a pink globule and peripheralizes the nucleus (Melamed-Wolinska bodies). Neoplastic islands occasionally have central foci of necrosis with replacement by eosinophilic fluid (cystic degeneration), or containing necrotic cellular debris, lymphocytes and plasma cells. The lamina propria is multifocally expanded by increased clear space and dilated lymphatics (edema), hemorrhage, and fibrin, and moderate numbers of lymphocytes, plasma cells, fewer macrophages, and eosinophils. The overlying and adjacent epithelium is multifocally partially lost (erosion) or mildly hyperplastic.

 

MORPHOLOGIC DIAGNOSIS: Urinary bladder: Urothelial (transitional cell) carcinoma, high grade, bichon frisé, canine.

 

CONDITION: Urothelial carcinoma, urothelial cell carcinoma, transitional cell carcinoma.

 

GENERAL DISCUSSION: 

• Formerly called “Transitional Cell Carcinoma” (still listed as such in many references)
• In general, urinary bladder neoplasia is uncommon; most common in dogs, occasional in cats, and rare in other species (exception: bovine enzootic hematuria); risk factors include exposure to carcinogens, female gender, obesity, and certain breeds (e.g. Scottish terrier West Highland White terrier, Shetland sheepdog, beagle, collie)
• Considered one of the most malignant tumors in dogs due to the likelihood of metastasis and resistance to treatment

 

PATHOGENESIS: 

• Cattle: Almost all lower urinary tract tumors are associated with bovine enzootic hematuria related to bracken fern and/or bovine papillomavirus-1 and BPV-2; carcinogens found in bracken fern include ptaquiloside, quercetin, shikimic acid, prunasin and aquilide A; these carcinogens act synergistically with papillomavirus to transform virus-associated papillomas into malignant carcinomas
  1. Pagetoid variant of urothelial carcinoma in situ reported in cow with enzootic hematuria and concurrent BPV-2 infection; tumor suppressor gene FHIT found to be absent in some pagetoid cells (indicative of late-stage neoplastic progression)
  2. Cyclin D1 dysregulation suspected in cattle with tumors related to enzootic hematuria
  3. Malignant neoplasms often have p63 mutations
• Various carcinogens suspected in other animals (industrial chemicals, tryptophan derivatives, cyclophosphamide); chronic irritation (cystitis, uroliths), foreign body reaction (sutures); Chronic Kidney Disease in cats may be associated in some cases of feline urothelial carcinomas (and other epithelial proliferative conditions) in the renal pelvis and renal crest (Bowsard J Comp Pathol 2021)
• Localized tumors: Papillary growth, in situ tumor, low grade, strong lymphoid response all positive prognostic indicators
• BRAF^7595E mutation associated with increased T_reg  recruitment (Maeda Vet Pathol 2021)
• Metastasis: Infiltrative/non-papillary growth, high tumor grade, deeper invasion (particularly through basement membrane and into lamina propria), vascular or lymphatic invasion, and peritumoral fibrosis all indicative of metastatic potential
  • About 50% of urothelial cell carcinomas metastasize 
    • Regional lymph nodes and lungs most often affected
    • Peritoneal implantation or lymphatic spread to the soft tissue and bones of the hindlimbs or vertebrae also common
    • Solitary metastasis to bone occurs occasionally
    • One case report of tonsillar metastasis in a dog (Mammone J Vet Diagn Invest 2022)
• Tumors in the bladder can grow and obstruct one or both ureters, resulting in secondary hydroureter/hydronephrosis
• Canine HER2 homolog (ERB2) expression increased in some dogs with urothelial cell carcinomas; no correlation with clinical factors (Tsuboi Vet Pathol 2019)

 

TYPICAL CLINICAL FINDINGS:

• Typically affects older dogs (average 9-11 years old)
• Hematuria, pollakiuria, cystitis, dysuria, urgency, abdominal pain, weight loss, weakness, lameness, and dyspnea

 

TYPICAL GROSS FINDINGS: 

• The trigone is the most common site, but any part of the bladder, the prostatic and lower urinary tract urethra may be involved, and may involve a large portion of the bladder, or can originate in the renal pelvis and invade into kidney
• Tumors may form papillary projections or may be flat plaques with a broad base
• Tumors are occasionally not visible grossly despite diffuse infiltration
• Hydronephrosis may develop secondary to ureteral obstruction
• Cutaneous metastases are mainly in the perineal, inguinal, or ventral abdominal region and often have epidermal erosion or ulceration

 

TYPICAL LIGHT MICROSCOPIC FINDINGS: 

• Histologically diagnostic appearance when within the urinary bladder; pleomorphic to anaplastic transitional epithelium (syncytia, atypical nuclei, and bizarre mitoses are common) that cover the mucosal surface in irregular layers, readily invade the lamina propria in solid nests and acini, and are often found within lymphatic vessels of the submucosa and tunica muscularis
• Cells may contain characteristic colorless to eosinophilic cytoplasmic inclusions (Melamed-Wolinska bodies) that are PAS-positive and stain positively for uroplakin
• Plasmacytoid and rhabdoid variants rarely described in dogs; characterized by discohesive cells with plasma cell-like or rhabdoid morphology (Lin, Vet Pathol 2018)
  • Potential IHC finding: Epithelial-mesenchymal transition and decreased e-cadherin expression
• The degree of desmoplasia corresponds to metastatic potential
• +/- Squamous or glandular metaplasia, desmoplastic areas can produce heterotopic bone
• Adjacent urothelium is hyperplastic
• Fibromyxoid stroma common in canine urothelial carcinoma, indicator of invasive growth -> poor prognostic factor (de Brot J Comp Pathol 2019)
• Histopathologic descriptions most valuable for clinical management when they include sampling of multiple sites and describe tumor architecture, tumor grade, and depth of invasion 
• Grading system: Low and high grade variants of urothelial carcinoma (Avallone Vet Pathol 2021)
  • High grade: Defined by features of malignancy (atypia, cellular and nuclear pleomorphism, mitotic activity, deep tissue and/or lymphovascular invasion)
  • Prognostic significance unknown; prospective studies needed

 

 

ADDITIONAL DIAGNOSTIC TESTS:

• Immunohistochemistry and molecular testing: 
  • Uroplakin III is a specific and sensitive marker for canine superficial (umbrella) urothelium but does not distinguish between neoplastic and non-neoplastic urothelium; expression may be lost in some high-grade neoplasms; can be helpful in determining metastasis
  • Tumor-associated glycoprotein 72 (TAG-72) used for IHC in human medicine; shown to be positive in 50% of canine urothelial carcinoma
  • COX-2 expressed in neoplastic epithelium but not normal urinary bladder epithelium; potential for targeted therapeutics
  • IHC used to validate vascular endothelial growth factor receptor 2 (VEGFR2) as a therapeutic target (Setyo, J Vet Diagn Invest 2023)
    • VEGFR2 overexpressed in urothelial carcinoma cells
    • Toceranib phosphate (Palladia; Pfizer) blocks VEGFR activity
  • Biomarkers S100A8, A9, and A12 potential diagnostic tools
  • BRAF^V595E mutation associated with tumor-produced CCL17, which plays a role in regulatory T cell recruitment; increased regulatory T cell concentrations in tumors associated with poor prognosis 
• Digital PCR tested for ERB2 copy number aberrations: sensitivity 35%, specificity 100% (Sakai et al 2020)
• Cytology: Epithelial cells with features of atypia (marked anisocytosis and anisokaryosis, variable N:C, pleomorphic nuclei), characteristic Melamed-Wolinska bodies (large pink cytoplasmic inclusions)

 

DIFFERENTIAL DIAGNOSIS:

Non-neoplastic bladder lesions:

• Polyps/polypoid cystitis: Common; singular/multiple nodules, on a stalk, <2cm diameter, Brunn’s nests are likely (isolated foci of mucosal invaginations into the submucosa forming solid nests), granulation tissue and inflammation of the submucosa
• Non-neoplastic epithelial abnormalities (NNEA): Hyperplasia, Brunn’s nests, cystic glandularis or cystitis cystica (Brunn’s nests with central lumen), glandular metaplasia, and nephrogenic adenoma (tubular-like structures in the lamina propria)

Other urinary bladder neoplasms:

• Papillomas and adenomas: Grossly identical; well-differentiated; lack of nuclear and cellular atypia; lack of invasion; may ulcerate resulting in hematuria; may undergo malignant transformation
  1. Bovine papillary hyperplasia can look similar and can cause urinary obstruction and hydronephrosis
• Squamous cell carcinoma: Arise in areas of squamous or glandular metaplasia; occurs most commonly in the distal two-thirds of the urethra of the bitch; usually nonpapillary infiltrative growths, often ulcerated, develop in areas of squamous or mucous metaplasia; less likely to metastasize than urothelial carcinomas
• Undifferentiated carcinomas: Rare, do not fit into othe subtypes
• Adenocarcinoma: Usually nonpapillary infiltrative growth of epithelium with glandular features, may contain Brunn nests (invaginated nests of urothelial cells), develop in areas of squamous or mucous metaplasia or urachal remnants 
• Nonepithelial tumors/ Mesenchymal tumors:
  • Leiomyoma/sarcoma: Solitary or multiple, circumscribed, firm, pale white to tan masses in the urinary bladder wall
  • Fibroma/sarcoma: Arise from lamina propria connective tissue and project into the bladder lumen as solitary nodules
  • Botryoid rhabdomyosarcoma: Rare, occur in young, large breed dogs; botryoid masses that occur at the trigone and project into the urinary bladder lumen 
  • Hemangioma/sarcoma

Other urinary tract neoplasms

• Prostatic carcinoma: Difficult to determine urothelial vs. prostatic origin; prostatic carcinoma favored by glandular differentiation, UP III and CK7 negative, PSA positive, PSMA positive
• Renal cell carcinoma: PAX8 positive, p63 negative

 

COMPARATIVE PATHOLOGY: 

• Urothelial cell carcinoma is reported in most domestic and a few exotic species
• Fallow deer: Urinary bladder lesions similar to bovine enzootic hematuria compatible with bracken fern intoxication is reported
• Cats: Urothelial cell carcinomas are rare but often aggressive
  • 30/30 cases with samples large enough to grade assessed as high grade (van der Weyden J Comp Pathol. 2021)
    • Similar histologic features as canine and human urothelial carcinoma
  • Inverted urothelial papilloma reported in one cat (Brunetti Vet Pathol 2022)
  • Species predilection in fishing cats
• Non-human primates: Urothelial carcinoma described in rhesus macaques cebeus monkeys and various prosimian species
• Russian tortoise: One case report of urothelial carcinoma arising from the renal pelvis (Hetterich J Comp Pathol 2023)
• Sloth and tenrec: Urothelial carcinoma reported 
• Short beaked common dolphin: Urothelial carcinoma reported in bladder

 

REFERENCES:

1. Abee CR, Mansfield K, Tardif S, Morris T. Nonhuman Primates in Biomedical Research: Volume 2: Diseases. 2nd ed. San Diego, CA: Elsevier; 2012.
2. Agnew D, Nofs S, Delaney MA, Rothenburger JL. Xenartha, Erinacoemorpha, Some Afrotheria, and Phloidota. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. London, UK: Academic Press; 2018:526. 
3. Avallone G, Rasotto R, Chambers J, et al. Review of Histological Grading Systemsin Veterinary Medicine. Vet Pathol. 2021;58(5)809-828.
4. Bowsard KL, Norris JM, Malik R, et al. Renal Crest Proliferative Lesions in Cats with Chronic Kidney Disease.  J Comp Pathol. 2021;187:52-62.
5. Brunetti B, Foglia A, Savini F, et al. Inverted Urothelial Papilloma in a Cat. Vet Pathol. 202259(1):138-142.
6. Ciancolo RE, Mohr FC. Urinary system. In:  Maxie MG, ed. Jubb, Kennedy and Palmer’s Pathology of Domestic Animals. Vol 2. 6^th ed. St. Louis, MO: Elsevier; 2016:447, 462-463.
7. de Brot S, Grau-Roma L, Stirling-Stainsby C, Dettwiler M, Guscetti F, Meier D, Scase T, Robinson BD, Gardner D, Mongan NP. A Fibromyxoid Stromal Response is Associated with Muscle Invasion in Canine Urothelial Carcinoma. J Comp Pathol. 2019;169:35-46.
8. Hetterich J, Schmidt V, Herth M, et al. Urothelial carcinoma in a Russian tortoise (Testudo horsfieldii). J Comp Pathol. 2023;200:18-22. 
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11. Lin SJ-H, Kao C-F, Wang F-I, et al. Urothelial Carcinomas of the Urinary Bladder with Plasmacytoid or Rhabdoid Features and Tendency of Epithelial-Mesenchymal Transition in 3 Dogs. Vet Pathol. 2018 ;55(5):673-677.
12. Maeda S, Yoshitake R, Chambers JK, et al. BRAF^V595E Mutation Associates CCL17 Expression and Regulatory T Cell Recruitment in Urothelial Carcinoma of Dogs. Vet Pathol. 2021;58(5):971-980.
13. Mammone RM, Havis B, Royal A, et al. Urothelial carcinoma with tonsillar metastasis in a dog. J Vet Diagn Invest. 2022;34(3)564-567.
14. Setyo LC, Donahoe SL, Shearer PL, et al. Immunohistochemical analysis of expression of VEGFR2, KIT, PDGFR-β, and CDK4 in canine urothelial carcinoma. J Vet Diagn Invest. 2023;35(2):109-115. 
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21. Van der Weyden L, O’Donnell M, Plog S. Histological Characterization of Feline Bladder Urothelial Carcinoma. J Comp Pathol. 2021;182:9-14.

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