[806] Renal Oncocytic Tumors with Hybrid Features Occurring in a Sporadic Setting: A Clinicopathologic Study of 22 Cases

Daniel Atherton, Kanishka Sircar, Pheroze Tamboli, Priya Rao. MD Anderson Cancer Center, Houston, TX

Background: Renal oncocytic tumors that show histologic features that overlap between renal oncocytoma (RO) and chromophobe renal cell carcinoma (ChRCC) comprise a rare subgroup of tumors that have been widely referred to as “hybrid oncocytic tumors” (HOT). Although originally described in patients with Birt-Hogg Dube (BHD) syndrome, these tumors are most frequently seen in the sporadic setting.
Design: We did a retrospective search of our databases (2005-2012) using search terms “hybrid tumor”, “oncocytosis” and “Birt-Hogg Dube”. Final analysis included 21 primary and one metastatic case. All available pathologic material was reviewed and clinical information was acquired from the medical record.
Results: Tumors were from 15 men 7 women. No patient had a diagnosis or showed stigmata suggestive of BHD syndrome. Tumor size ranged from 1.1 to 25 cm (mean 5.5). Six patients presented with more than 1 tumor in the resected kidney wherein the dominant tumor was associated with areas of renal oncocytosis. Six tumors were associated with perinephric/renal sinus fat invasion (pT3=6, pT1=15). One additional tumor showed involvement of a large vessel within the renal sinus. Most cases showed true hybrid morphology and had areas within the same tumor that resembled both RO and ChRCC. In most cases areas resembling RO predominated and gradually transitioned to areas resembling ChRCC. The single case of a metastatic tumor within the liver occurred in a patient with a remote history of RO. The liver lesion histologically closely resembled a RO but showed diffuse CK7 staining thus resulting in the diagnosis of HOT. Immunohistochemical stains were performed in 20 cases. All cases were negative for vimentin. The majority of cases (15/20) showed only focal staining for CK7, which was helpful in the distinction from ChRCC. In 2 instances, tumors resembled RO histologically but were classified as HOT's due to diffuse staining with CK7. Follow up information of greater than 6 months was available in 15 cases (range 6-59 mos; mean 25 mos). None of the cases with primary resections resulted in recurrence or metastasis.
Conclusions: Renal hybrid oncocytic tumors are rare renal neoplasms which occur in both the sporadic and syndromic setting. Tumors have histologic features that overlap between RO and ChRCC and may pose a diagnostic dilemma for the pathologist. Tumors generally follow an indolent clinical course even in the setting of locally advanced tumor at diagnosis. There is a definite potential for metastasis which makes accurate classification of these neoplasms critical.
Category: Genitourinary (including renal tumors)

Tuesday, March 5, 2013 8:00 AM

Proffered Papers: Section A, Tuesday Morning


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