[842] PAX8 Is a Sensitive Marker for Papillary Renal Cell Carcinoma: Comparison with PAX2.

Arjumand Husain, Shuhong Liu, Asli Yilmaz, Kiril Trpkov. University of Calgary and Calgary Laboratory Services, AB, Canada

Background: PAX8 and PAX2 are transcription factors which have been implicated in the oncogenesis of the renal, Müllerian and thyroid neoplasms. Recent studies suggested that PAX8 and PAX2 can be useful diagnostic markers in the evaluation of primary and metastatic renal tumors. In particular, PAX8 has been shown to be a highly sensitive marker for papillary renal cell carcinoma (96%; Mod Pathol 2010;23 suppl1;178A). To our knowledge, PAX8 and PAX2 immunohistochemistry (ICH) profiles have not been compared in PRCC and other common renal tumors.
Design: We compared the ICH staining of PAX8 and PAX2 in a tissue microarray (TMA) generated to evaluate 85 PRCC. In addition, 13 common renal tumors were included in the TMA: 5 clear cell (CcRCC), 3 chromophobe (ChRCC) and 5 oncocytomas. Staining intensity, which typically demonstrates nuclear pattern for both markers, was scored as 0 (negative), 1+ (weak), 2+ (moderate), 3+ (strong). The extent of staining was scored as focal (≤25% of cells) or diffuse (>25% of cells).
Results:

PAX8 and PAX2 expression: comparison in PRCC and other common renal tumors

		PRCC (n=85)	CcRCC (n=5)	ChRCC (n=3)	Oncocytoma (n=5)
PAX8	0	2 (2%)	0 (%)	0 (0%)	0 (0%)
	1+	24 (28%)	2 (40%)	2 (67%)	2 (40%)
	2+	37 (44%)	2 (40%)	1 (33%)	3 (60%)
	3+	22 (26%)	1 (20%)	0 (0%)	0 (0%)
PAX2	0	11 (13%)	1 (20%)	2 (67%)	1 (20%)
	1+	42 (50%)	2 (40%)	1 (33%)	3 (60%)
	2+	25 (29%)	2 (20%)	0 (0%)	1 (20%)
	3+	7 (8%)	0 (0%)	0 (0%)	0 (%)

PAX 8 was positive in 98% of PRCC. Overall, PAX8 demonstrated moderate to strong (2-3+) staining in 70% of PRCC (vs. 37% for PAX2) and 60% of CcRCC (vs. 20% for PAX2). PAX8 was diffusely positive in all evaluated renal tumors. Although PAX2 was positive in 87% of PRCC, 42/74 (57%) of positive PRCC showed 1+ intensity. PAX2 was focally positive in 11/74 (15%) PRCC and in 1/5 (20%) oncocytomas and it was diffusely positive in all evaluated CcRCC and ChRCC.
Conclusions: PAX8 is a sensitive marker for PRCC and demonstrated superior profile than PAX2 regarding the ICH staining frequency, intensity and the extent of staining. PAX8 may be a useful addition to the ICH panel when evaluating a possible PRCC in a limited biopsy core or in the differential diagnosis of an unknown metastatic carcinoma with papillary differentiation. PAX8 was also a more reliable marker than PAX2 in the evaluation of CcRCC. Both PAX8 and PAX2 appear to be of limited diagnostic utility in the evaluation of ChRCC and oncocytoma.
Category: Genitourinary (including renal tumors)

Wednesday, March 2, 2011 9:30 AM

Poster Session V # 108, Wednesday Morning