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Regular Article |



From the Department of Pathology,*
The Johns Hopkins
Hospital, Baltimore, Maryland; the Wolfson Childrens
Hospital,
Jacksonville, Florida; Loma Linda
University,
Loma Linda, California;
and the Cytogenetics Laboratory,
the Nemours
Childrens Clinic, Jacksonville, Florida
| Abstract |
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| Introduction |
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We report two cases of a hitherto undescribed pediatric renal neoplasm that is distinctive at the microscopic, immunohistochemical, ultrastructural, and genetic levels. Although their morphological features suggest that they represent an epithelial neoplasm, these tumors are nonimmunoreactive for epithelial markers. Like AMLs, they are focally immunoreactive for melanocytic markers; however, their ultrastructural features are distinct from both RCC and AML. On cytogenetic analysis, these tumors bear the identical t(6;11)(p21.1;q12) chromosome translocation, supporting the concept that they represent a distinctive morphological and molecular entity.
| Materials and Methods |
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For immunohistochemical labeling, four-µm sections were deparaffinized with xylene for 30 minutes and rehydrated using graded ethanol concentrations. Antigen retrieval was performed using either protease digestion or steaming. Immunoperoxidase labeling using the avidin-biotin-peroxidase complex technique and 3',3'-diaminobenzidine as chromagen was performed with the automated Biotek-1000 staining system (Ventana/Biotek Solutions, Inc., Tucson, AZ). The antibodies used, vendors, pretreatments, and dilutions were as follows: epithelial membrane antigen (EMA) (steam, 1:1000; DAKO, Carpinteria, CA), desmin (steam, 1:20,000; DAKO), S100 protein (steam, 1:6000; DAKO), smooth muscle actin (steam, 1:200; Boehringer Mannheim, Indianapolis, IN), cytokeratin 7 (protease, 1:50; DAKO), vimentin (steam, 1:100; Zymed, San Francisco, CA), cytokeratin AE1/AE3 (protease, 1:2000; Boehringer Mannheim), cytokeratin Cam5.2 (protease, prediluted; Becton Dickinson, San Jose, CA), HMB45 (steam, 1:125; DAKO), and Melan A (steam, 1:800; DAKO). To avoid biotin-related staining artifacts, labelings for HMB45, Melan-A, Cam 5.2, and cytokeratin 7 were repeated using the DAKO Envision system instead of the avidin-biotin-peroxidase technique.
For ultrastructural analysis, fresh samples of tumor were fixed in 3% glutaraldehyde and then postfixed in 1% osmium tetroxide, followed by dehydration and embedding in epoxy resin. Ultrathin sections stained with lead citrate and uranyl acetate were examined in a Philips CM12 transmission electron microscope.
For cytogenetic analysis, tumor tissue from each patient was prepared by mincing and digestion with collagenase type II, then cultured for 2 to 4 days. Cells were harvested after 1 to 5 hours exposure to colcemid at 0.6 µg/ml, slides were made and G-banded after standard protocols. Twenty cells were analyzed from tumor 1 and six mitotic figures were analyzed from tumor 2. Chromosome abnormalities were described according to the 1995 International System for Human Cytogenetic Nomenclature guidelines. An additional slide for tumor 1 was made for spectral karyotyping (SKY) analysis according to the protocol supplied with the probe kit (Applied Spectral Imaging, Carlsbad, CA). The SKY probe was a mixture of whole chromosome paint probes for each chromosome, combinatorially labeled with five fluorochromes. Briefly, the probe was denatured, pre-annealed with Cot-1 DNA for 1 hour, hybridized with the separately denatured chromosomes for 48 hours, washed, and detected according to ASI (Carlsbad, CA) protocol. Eleven metaphases were analyzed for hybridization quality, and four representative cells were chosen for complete analysis. Metaphase images were acquired using a standard epifluorescence microscope equipped with a 150 W xenon lamp, a 63x oil-immersion objective, and the ASI SpectraCube SD200 system. 4',6-Diamidino-2-phenylindole-counterstained images were captured with a 100 W mercury lamp and inverted by Sky View software (ASI) to permit enhanced banding.
| Results |
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Patient 1 was an 18-year-old African-American male with a past medical history significant only for asthma who presented with gross hematuria associated with left flank pain after traumatic injury. Abdominal ultrasonography and computed tomography scan demonstrated a 7-cm left renal mass. The patient underwent an uncomplicated left radical nephrectomy. He is known to be alive 18 months after surgery, although the status of his tumor is not known. He has not received postoperative chemotherapy or radiation therapy.
Patient 2 was a 10-year-old African-American male with a past medical history significant for precocious puberty associated with elevated serum somatomedin C levels. He developed painless hematuria, and was found to have a right renal mass. The patient underwent an uncomplicated right radical nephrectomy. He has not received postoperative chemotherapy or radiation therapy. The patient is alive and free of tumor by renal ultrasonography and chest X-ray 26 months after surgery. Computed tomography scan performed 12 months after surgery similarly showed no evidence of tumor.
In neither case was a history of von Hippel-Lindau syndrome or of tuberous sclerosis syndrome elicited.
Gross Findings
Patient 1s tumor was located in the upper pole of the left
kidney, and measured 7 x 7 x 6.5 cm. On cut section, the
tumor was well circumscribed, tan-brown in color, and had a
multinodular appearance. Slightly more yellow nodules could be
appreciated within (Figure 1)
. Neither
necrosis nor hemorrhage was identified. The tumor was confined by the
renal capsule, but extended into the renal pelvis. Patient 2s tumor
replaced nearly the entire anterior and central kidney, with normal
kidney discernable only in the medial upper and lower poles. The tumor
measured 12.2 x 9.7 x 7.1 cm, and on cut section it too was
primarily tan-brown and nodular, with other more golden yellow areas.
Small blood-filled cysts measuring up to 3.4 cm were also identified,
but necrosis was not seen. This tumor also was confined to the kidney.
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The two tumors were distinctive and virtually identical
at the microscopic level, and therefore they are described together.
Each tumor was surrounded in part by a thin, focally calcified, fibrous
capsule. However, each tumor permeated this capsule multifocally to
infiltrate superficially among native renal tubules. The tumors were
predominantly composed of nests of polygonal cells with well-defined
cell borders, separated by thin capillaries (Figure 2)
. Occasional staghorn-shaped,
thin-walled vessels were also present. The capillaries became
inapparent in more cellular, solid areas of the tumor. In other areas,
the tumor demonstrated an acinar growth pattern (Figure 3)
. The polygonal tumor cells had
variable cytoplasmic morphology: some cells had completely clear
cytoplasm, others had pale, sparsely granular, pink cytoplasm, whereas
others had densely granular, eosinophilic cytoplasm (Figure 4)
. Nuclei were generally rounded,
although at high power one could appreciate the slightly irregular
nuclear contours and small central nucleoli. Also scattered throughout
these tumors were 10 to 50 cell clusters of smaller cells that
characteristically surrounded small rounded nodules of hyaline,
basement membrane-like material, yielding an appearance reminiscent of
Call-Exner bodies. These clusters often appeared to be present within
acini formed by the larger, polygonal cells (Figure 3)
, and were
particularly prominent in cytological smear preparations made from case
1 (Figure 5)
. Overall, the variably clear
to eosinophilic cytoplasm of the polygonal cells and the scattering of
smaller cells gave these tumors a polymorphous appearance (Figure 4)
.
The hyaline material was positive on periodic acid-Schiff stain, both
before and after diastase treatment, and on methenamine silver stain,
consistent with basement membrane material (not shown).
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Immunohistochemical Findings
Each tumor, particularly the more eosinophilic cells, was
immunoreactive for vimentin. The tumors were nonimmunoreactive for a
wide range of epithelial markers including cytokeratin AE1/AE3,
cytokeratin Cam 5.2, cytokeratin 7, and EMA. The epithelial markers
highlighted the infiltrative border of these tumors, as scattered,
intensely keratin-positive entrapped renal tubules were identified at
the tumors leading edge (Figure 6)
. A
moderate number of epithelioid tumor cells labeled focally but
intensely for the melanocytic markers HMB45 and Melan-A, although these
stains were not diffusely positive and did not label the smaller cells
(Figure 7)
. Stains for S100 protein,
desmin, smooth muscle actin, and chromogranin A did not label the tumor
cells. The pink hyaline material about which the smaller cells were
clustered labeled strongly for type 4 collagen. This marker also
highlighted the tumors prominent capillary vasculature (Figure 8)
.
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Electron microscopic examination revealed polygonal cells with
abundant mitochondria and scattered membrane-bound granules, some also
containing prominent amounts of glycogen. The most prominent feature
was the presence of localized pools of duplicated basement
membrane material surrounded by clusters of tumor cells (Figure 9, A and B)
. The larger nests of tumor
cells were also delineated by basement membrane. Occasional cell
junctions were identified (Figure 9B)
, but true desmosomes were not.
Cytoplasmic filaments were not prominent.
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All G-banded cells from both patients tumors contained a
balanced translocation between chromosomes 6 and 11 as the sole
abnormality. Although the translocation for patient 1 was initially
interpreted as a whole-arm translocation, t(6;11)(p10;p10) (Figure 10)
, SKY analysis showed the
translocation breakpoints to be clearly within the short arm of
chromosome 6 and the long arm of chromosome 11 (Figure 11)
. The breakpoint in the der(11)
seems to be within 11q12 or at the 11q12-q13 junction; however, we
cannot exclude the possibility that the breakpoint occurs in the light
material of the very proximal 11q13.1. The description of the karyotype
was corrected to 46, XY, t(6;11)(p21.1;q12) for both patients.
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| Discussion |
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The histogenesis of these tumors is not clear, as their ultrastructural features do not match those of any normal cell within the kidney. Production of duplicated basement membrane material is a characteristic of two neoplasms, adenoid cystic carcinoma and cylindroma, which are far different from these lesions at the morphological and immunophenotypic levels and not well-recognized to occur within the kidney.10 It remains possible that these tumors are related to epithelioid AML, as is suggested by their morphology and reactivity for melanocytic markers. Epithelioid AML is one of a family of lesions thought to be derived from perivascular epithelioid cells (PECs).11 These cells are found in many of the hamartomatous lesions associated with tuberous sclerosis syndrome, such as AML, cardiac rhabdomyoma, and pulmonary lymphangioleiomyomatosis.12 PECs classically co-express myogenic and melanocytic markers; however, they are thought to be capable of dramatically modulating their morphology and immunophenotype. For example, spindled PECs express muscle markers like actin more strongly than HMB45, whereas the converse is true of epithelioid PECs. Because occasional epithelioid AML have been found to express cytokeratins6,13 and have been associated with overt RCC,14,15 some have also postulated that PECs can modulate into a fully epithelial phenotype.16,17 Modulation of PECs toward adipocytic differentiation can explain predominantly adipocytic AML and microhamartomas of the kidney. Perhaps the current lesions represent another phenotype toward which the PECs can modulate, one which is characterized by abundant basement membrane production and only focal HMB45 immunoreactivity. In favor of this theory is the fact that PECs of AML are normally associated with basement membrane material, although it is usually discontinuous. It is intriguing that focal intense HMB45 immunoreactivity similar to that which we observed in these tumors has been reported in two other lesions, the leiomyoma of the renal capsule18 and cardiac rhabdomyoma.12 The latter is associated with the tuberous sclerosis syndrome.
Although the t(6;11)(p21.1;q12) chromosome translocation has not previously been reported, it is of interest that loci near each breakpoint involved in the translocation have been implicated in renal disease. Translocations involving 11q13 are implicated in a subset of renal oncocytomas;19,20 the reciprocal partners for these translocations have most frequently been located on the long arm of chromosome 921,22 and the long arm of chromosome 5 (specifically 5q35).23,24 11q13 is known to harbor mitochondrial genes, and disruption of this locus is postulated to effect the mitochondria-rich phenotype of oncocytoma. Along these lines, it is intriguing that the current lesions demonstrate prominent mitochondria at the ultrastructural level, although not to the degree of oncocytoma. However, the published karyotypes from oncocytoma seem to show a breakpoint in distal 11q13, and a published fluorescence in situ hybridization study24 places it within 11q13.3. Our tumors show a breakpoint barely past the centromere, in 11q12 or very proximal 11q13.1, and thus rearrangement at the same locus seems unlikely. The 6p21 locus has been implicated in multicystic renal dysplasia, in one case via a t(6;19)(p21;q13.1) translocation that disrupts the CDC5L gene.25,26 Neither of the loci implicated in tuberous sclerosis (TSC1 at 9q34 or TSC2 at 16p13.3) are involved in the t(6;11)(p21.1;q12) translocation. However, deletion of 11q13 was identified in 2 of 11 AMLs studied by comparative genomic hybridization, including one epithelioid variant.27
In summary, we present two cases of a distinct tumor type characterized by epithelioid cell morphology, immunoreactivity for melanocytic markers, prominent basement membrane material ultrastructurally, and a unique t(6;11)(p21.1;q12) chromosome translocation. These tumors seem to be rare, although we have subsequently encountered several morphologically and immunohistochemically similar lesions from which material for cytogenetic analysis was unavailable. Although both of our cases were identified in young patients, it is possible that this reflects the bias inherent in our clinical practice. These cases illustrate the challenges that pediatric renal tumors can pose at the morphological level, and the value of cytogenetics in defining distinctive entities.
| Acknowledgements |
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| Footnotes |
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Accepted for publication February 16, 2001.
| References |
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