[724] P16 Expression in Small Cell Carcinoma of the Urinary Bladder

N Buza, A Finkelstein, P Hui, P Cohen, V Parkash. Yale University School of Medicine, New Haven, CT

Background: Small cell carcinoma (SmCC) of the urinary bladder is a rare malignancy accounting for less than 1% of all urinary bladder carcinomas. The diagnosis is usually made on morphologic grounds with the help of immunohistochemistry for neuroendocrine differentiation. However, staining for neuroendocrine markers is inconsistent and ranges between 30-70%. Alterations in the p16-Rb pathway and overexpression of p16 tumor suppressor protein is present in a high percentage of SmCCs of the lung and is absent in the majority of poorly differentiated squamous cell carcinomas of the lung. These data suggest that p16 immunohistochemistry - as part of an immunohistochemical panel - could be useful in the diagnosis of urinary bladder SmCCs. To our knowledge, this is the first study investigating p16 expression in SmCCs of the urinary bladder.
Design: We identified 14 cases of SmCCs of the bladder (either pure or admixed with other high grade components) and 16 cases of high grade urothelial (transitional cell) carcinoma (HG-TCC) of the bladder diagnosed at our institution. After reviewing the H&E slides, the following immunohistochemical panel was performed on a representative block from each case: p16, p63, CK20, CK7, chromogranin (Chr), synaptophysin (Syn), and CD56 (N-CAM).
Results: P16 expression was significantly higher in SmCCs (92.8%) compared to HG-TCCs (43.7%). P63 and CK20 on the other hand, were positive in majority of HG-TCCs (80% and 53.3%, respectively). None of the SmCCs stained with p63 and only 15.4% of cases were focally immunoreactive with CK20. CK7 immunostain was positive in 61.5% of the SmCCs and in 80% of the HG-TCCs. The sensitivity of the traditional neuroendocrine markers was low, ranging between 28.6% (Chr) and 69.2% (CD56) in SmCCs.

Percent of positive cases

	P16	P63	CK20	CK7	Chr	Syn	CD56
SmCC	92.8%	0%	15.4% (focal)	61.5%	28.6%	64.3%	69.2%
HG-TCC	43.7%	80%	53.3%	80%	0%	6.7% (rare cells)	0%

Conclusions: A p16 +, p63 - and CK20 - immunohistochemical profile is typical of SmCC of the urinary bladder, whereas HG-TCC is p16 +/-, p63 + and CK20 +. Overexpression of p16 in SmCC of the urinary bladder also provides further evidence for a link between alterations in the p16-Rb pathway and neuroendocrine differentiation.
Category: Genitourinary (including renal tumors)

Wednesday, March 11, 2009 9:30 AM

Poster Session V # 110, Wednesday Morning