[984] Pigmented Microcystic Chromphobe Renal Cell Carcinoma: A Peculiar Morphological Variant. Clinicopathologic, Immunohistochemical, and Molecular Cytogenetic Study of 33 Cases

Francisco J Queipo, Angel Panizo, Antonio Tienza, Irene Rodriguez, Jesus J Sola, Javier Pardo. Clinica Universidad de Navarra, Pamplona, Spain; Complejo Hospitalario de Navarra "A", Pamplona, Spain

Background: The chromophobe renal cell carcinoma (CRCC) is a tumor that exhibits two different morphologic subtypes. Pigmented microcystic and cribriform (PMCRCC) is a new morphologic subtype recently described. The aim of this study is to investigate the clinical, histologic, IHC and cytogenetic profile of 33 cases of PMCRCC.
Design: We identified 33 cases in 32 patients of PMCRCC variant. In all cases we performed a detailed clinical, morphological, and IHC study. Chromosomal abnormalities of chromosomes (CHRO) 7 and 17 were evaluated by automated dual-color silver-enhanced in situ hybridization (SISH) on paraffin-embedded tissue. CHRO imbalance was defined on the basis of changes in both CHRO index and signal distribution: when only one of these was altered, this was classified as a tendency to gain or loss.
Results: Age range was 41 to 83 yrs, 28 males and 4 women. 14 cases were in the right kidney, 16 in the left and 1 bilateral. The diameter of the tumors ranged between 1 and 10 cm (mean 4 cm). 23 were pT1, 6 pT2, and 2 pT3. Grossly the tumors were solid, with a brown dark color. Microscopically, tumors consisted of eosinophilic cells arranged in microcysts or microalveoli in a cribriform pattern, and focally formed adenomatous structures. Necrosis foci were seen in 5 cases. All tumors showed extracellular dark brown pigment, although in some cases also in the tumor cytoplasm. The pigment stained with Masson Fontana and focally with iron stain. There were microcalcifications in all cases. No case presented sarcomatoid transformation. All tumors were positive for CK7, EMA, and Claudin-7. Tumors were negative for RCC, AMACR, HMB45, and S100. Tumors showed both multiple monosomies and polysomies. Monosomy of CHRO 17 was seen in 2/24 cases, and 12 showed a trend towards loss. Monosomy of CHRO 7 was present in 1/16 cases. Polysomy of chromosome 17 and 7 was found in 1/24 and 10/16 cases, respectively. The median follow-up of the 32 patients was 47.5 months (range 3-156): 30 were alive without disease, and 2 were alive with hepatic metastasis.
Conclusions: The PMCRCC constitute a morphologically distinctive and unusual variant that expands the spectrum of the CRCC. PMCRCC show an immunohistochemical profile and monosomy of CHRO 17 corresponding to usual forms of CRCC. However polysomy of CHRO 7 was common, unlike CRCC. This study confirms that these tumors have a low aggressive behavior, with absence of sarcomatoid dedifferentiation, and exceptional distant metastases.
Category: Genitourinary (including renal tumors)

Tuesday, March 20, 2012 9:30 AM

Poster Session III # 161, Tuesday Morning


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