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17 October 2018 - Case of the Week #466

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Case of the Week #466

Clinical history:
70 year old woman, history unknown, with bladder tumor resection (TURBT).

Histopathology images:

What is your diagnosis?

Lipid cell variant of urothelial carcinoma

Test question (answer at the end):
Which of the following is true about lipid cell variant of urothelial carcinoma?

A. It is S100 and vimentin positive
B. The lipid cell component usually comprises greater than 50% of the urothelial carcinoma
C. The lipid cells are negative for panCK and CK7, contributing to diagnostic challenges with lipoblasts and liposarcoma
D. The lipid cells express panCK and CK7 and are negative for mucin, distinguishing this entity from others in the differential diagnosis

Lipid cell (lipid rich, lipoid cell) variant of urothelial carcinoma (UC) is an uncommon WHO recognized variant of invasive urothelial carcinoma characterized by large signet ring lipoblast-like cells with single or multiple clear cytoplasmic vacuoles indenting the nucleus (Eur Urol 2016;70:93). It is primarily seen in men, median age 74 years, who present with hematuria (Am J Surg Pathol 2010;34:371). Lipid cell variant of UC has been described predominantly in the bladder, with rare cases in the ureter and renal pelvis (Am J Surg Pathol 2010;34:371, Case Rep Oncol 2015;8:515, Am J Surg Pathol 2007;31:770, Pathology 2016;48:388, Journal of Clinical Oncology 2018;36:487).

Distinct macroscopic features are not well documented. Microscopically, it coexists with high grade conventional and papillary UC, and shows identical loss of heterozygosity (LOH) patterns with the coexistent conventional UC (Am J Surg Pathol 2010;34:371), supporting a shared clonal origin. The cells express panCK, CK7, CK20 (variable), EMA, thrombomodulin (variable) and are negative for S100 and vimentin (Am J Surg Pathol 2010;34:371). The presence of lipid has been supported by ultrastructural studies; this component comprises 10 - 50% of the tumor (Am J Surg Pathol 2010;34:371).

Other urothelial carcinoma variants, particularly micropapillary or plasmacytoid variants, may coexist with the lipid cell variant (Case Rep Oncol 2015;8:515, Am J Surg Pathol 2010;34:371, Journal of Clinical Oncology 2018;36:487). In a multi-institutional study of lipid cell variant of UC, the 27 studied patients usually presented at high stage and had associated poorer outcomes; 60% had died after an average of 33 months (Am J Surg Pathol 2010;34:371, Eur Urol 2016 Jul;70:93). Treatment is similar to conventional high grade invasive urothelial carcinoma.

The differential diagnosis of lipid cell variant of UC includes clear cell (glycogen rich) urothelial carcinoma, adenocarcinoma with signet ring features, sarcomatoid carcinoma and liposarcoma. Clear cell UC contains intracytoplasmic periodic acid-Schiff (PAS) positive and diastase sensitive glycogen, rather than lipid, and lacks lipoblast-like nuclear indentations. Signet ring features may be seen in urothelial carcinoma, particularly plasmacytoid UC and UC with glandular differentiation, the later of which often has areas with more enteric histology and immunophenotype reminiscent of colonic adenocarcinoma. Signet ring features may also been seen in metastatic carcinomas. Unlike some signet ring adenocarcinomas, lipid cell variant of UC is consistently negative for mucin (Am J Surg Pathol 2010;34:371) and has areas of conventional UC, distinguishing it from a metastasis. Although sarcomatoid carcinoma may have heterologous liposarcomatous elements, lipid cell variant of UC lacks the prominent high grade spindled features of sarcomatoid carcinoma and does not usually coexist with the sarcomatoid variant.

Finally, liposarcoma, either primarily or secondarily involving the genitourinary tract, may enter the differential. The presence of cytokeratin and CK7 positive lipoblast-like cells and conventional urothelial carcinoma point to the correct diagnosis of lipid cell variant of UC.

Test question answer:
The lipid cells express panCK and CK7 and are negative for mucin, distinguishing this entity from others in the differential diagnosis.
This and the presence of conventional high grade urothelial carcinoma are helpful diagnostic features in the differential diagnoses of lipid cell variant of urothelial carcinoma with adenocarcinomas with signet ring features, sarcomatoid carcinoma and liposarcoma.

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