[824] Detailed Histologic Evaluation of Renal Cell Carcinoma (RCC) Subtypes in 138 Metastatic Tumors with Emphasis on Homology with Primary Site

Elena E Chang, Daniel J Luthringer, Mariza de Peralta-Venturina, Bonnie Balzer, Sijian Wang, Julie M Wu, Mahul B Amin. Cedars-Sinai Medical Center, Los Angeles, CA

Background: RCC is known for its propensity to metastasize, and even present initially at a metastatic site. Accurate recognition of distinct subtypes of RCC, especially when metastatic, is important as therapies differ between them. Detailed histologic information about metastatic RCC is scarce.
Design: We reviewed 136 metastatic tumors in 103 patients. In 63 metastases in which 45 primaries were available for comparison, the aim was to understand the differences in morphology between the two. In metastasis-cases only (73), the aim was to determine if we could subtype the RCC based on the histology of the metastasis alone.
Results: The primaries consisted of 28 clear cell RCC (CCRCC), 9 non-CCRCC (2 papillary, 2 chromophobe, 2 collecting duct, 1 TFE3-associated; 1 ACKD-associated, 1 sarcomatoid), and 8 unclassified. For 26/37(70%) of metastatic CCRCC, there was overall concordance of histologic pattern with the primary or the metastasis could be diagnosed as a clear cell carcinoma based on histology alone. However in the primary tumor, clear cell histology predominated over eosinophilic histology (2.2:1), whereas in metastatic cases the ratio was reversed (1:2). The discordant CCRCC metastatic tumors more commonly showed solid growth pattern (8/11) in which tumor cells were predominantly eosinophilic (average 95%). In 73 metastases without primaries, 8 tumors could not be subtyped, due to mostly solid and/or papillary architecture. 64 of metastases-only cases were CCRCC based on sinusoidal architecture and/or clear cell features; these metastases showed increased clear:eosinophilic histology (1.2:1). Rhabdoid morphology was seen in multiple metastatic sites. Only 24% of nonCCRCC and 12.5% of unclassified RCC were concordant. In tumors with discordant histology, the metastases frequently exhibited solid or papillary architecture (18/20) with mainly eosinophilic cells (95%).
Conclusions: 1) When determining the subtype of RCC at a metastatic site, correlation with the histology of the primary, if available, is necessary. 2) The histology of the metastasis in CCRCC and non-CCRCC may be discordant with the primary tumor due to greater proportions of "higher grade" components/dedifferentiation (solid appearance, eosinophilic cytoplasm, rhabdoid morphology), which may not always be present in the primary. 3) Given our experience, in the era of targeted therapies, ancillary discriminatory immunohistochemical markers or molecular modalities are still needed for accurate subtyping of RCC at metastatic sites.
Category: Genitourinary (including renal tumors)

Tuesday, March 5, 2013 9:30 AM

Poster Session III # 94, Tuesday Morning


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