Pediatric Pathology

Tuberous Sclerosis Associated Renal Cell Carcinoma

Mark A. Lovell
The Children's Hospital
University of Colorado Denver
Aurora, Colorado


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Clinical History
An obese 14-year-old Hispanic male presented with 24 hours of gross hematuria, right flank pain, and frequent urination with blood present. He had mild, constant dull right flank pain without radiation. His BUN was 37 and creatinine was 3.8. CT showed a 3 cm well-circumscribed homogenous, hypervascular mass in the anterior medial-superior pole of the right kidney which was excised.

Multiple skin colored papules were noted on his cheeks and chin with some small nodules on the nose and a hypopigmented macula was present on his back. Multigenerational family members have similar skin lesions and his brother also had seizures.


Slide 1
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Figure 1
Gross photograph showing cut surface of renal mass.
Figure 2
Low power view shows multiple cysts and abundant chronic interstitial inflammation in the non-neoplastic kidney.
Figure 3
High power view shows several cysts with variably atypical lining.

Figure 4
Low power view highlights glomerular sclerosis and periglomerular fibrosis.
Figure 5
Low power view shows the tumor/kidney interface.
Figure 6
The tumor has solid and tubular components.

Figure 7 - CAM 5.2
Strong membranous immunoreactivity for CAM 5.2 (Cell Adhesion Molecule 5.2) is present in the tubular component of the tumor.
Figure 8 - epithelial membrane antigen
Strong membranous immunoreactivity for EMA (Epithelial Membrane Antigen) is present in the tubular component of the tumor.
Figure 9 - melanoma-associated antigen
The tumor cells do not show immunoreactivity for MAA (Melanoma Associated Antigen).

Figure 10 - Oil Red O
The tumor cells do not show positivity for Oil Red O.
Figure 11
A: Ultrastructural analysis shows epithelial cells without abundant lipid. B: High power ultrastructural view shows several cup-shaped, electron-dense granules.

Pathologic Findings
A partial right nephrectomy specimen contained a red-brown 2.5 cm mass surrounded by a margin of renal tissue. This rim of renal parenchyma displayed 1-2 mm cysts lined by dysplastic, often papillary epithelium with psammomatous calcification. In addition, foci of glomerulosclerosis and chronic interstitial inflammation were seen. However, a sclerotic rim demarcated the tumor from the surrounding kidney. The tumor was composed of cells with clear and eosinophilic cytoplasm with round nuclei with small nucleoli. These were immunopositive for epithelial differentiation and negative for melanocytic and smooth muscle differentiation. Ultrastructural examination found abundant glycogen and poorly developed intercellular junctions without convincing evidence of lipocytic or smooth muscle differentiation; however, scattered clusters of cup-shaped, electron dense granules were noted, although not typical of premelanosomes.

Discussion
This patient's clinical presentation is classic for tuberous sclerosis complex (TSC); however, the clinical differential diagnosis of cutaneous lesions associated with renal masses includes two other interesting syndromes.

Facial fibrofolliculomas, trichodiscomas and acrochordons of the face, head and upper body are seen in Birt-Hogg-Dubé syndrome which involves mutations on chromosome 17p11.2 in the FLCN gene encoding folliculin, a protein involved in cell signaling. The renal tumors are multiple and bilateral renal cell carcinomas with papillary or chromophobe histology or may be oncocytomas. Affected individuals may also be at risk for spontaneous pneumothoraces and colorectal cancer.

Cutaneous leiomyomas can be seen in Hereditary Leiomyomatosis and Renal Cell Carcinoma syndrome which involves mutations on chromosome 1q42.1 in the FH gene encoding fumarate hydratase, a Krebs cycle enzyme. The renal tumors are type 2 papillary renal cell carcinomas or collecting duct carcinomas. Uterine leiomyomata are also a common feature, with leiomyosarcomas occasionally developing.

In contrast to these interesting but unusual conditions, TSC is a highly penetrant (95%) autosomal dominant genetic disease with an incidence of approximate 1 in 6,000 to 11,000 live births. Of note, two-thirds of cases have no family history and represent de novo mutations. In cases in which uninvolved parents have affected children the parental origin of the genetic mutation (gonadal mosaicism) is equal. In addition, patients may be somatic mosaics.

The phenotypic manifestations in the table below provide the clinical criteria for the diagnosis of tuberous sclerosis (2 major features definite TSC; 1 major and 1 minor probably TSC; 1 major or 2 minor possible TSC).

Major Feature Minor Feature
Facial angiofibromas of forehead plaques Multiple randomly distributed pits in dental enamel
Nontraumatic ungula or periungual fibromas Hamartomatous rectal polyps
Hypomelanotic macules (3 or more) Bone cysts
Shagreen patch (connective tissue nevus) Cerebral white matter radial migration lines
Muliple retinal nodular hamartomas Gingival fibromas
Cortical tuber, subependymal nodule or giant cell astrocytoma (SEGA) [each is major] Nonrenal hamartoma
Cardiac rhabdomyoma, single or multiple Retinal achromatic patch
Lymphangiomyomatosis "Confetti" skin lesions
Renal angiomyolipoma Multiple renal cysts

Roach & Sparagana 2004

The phenotypic variability of TSC is a consequence of the genetic heterogeneity which underlies this clinical syndrome. The two major genes involved are TSC1 on chromosome 9q34 and TSC2 on chromosome 16p13. These two genes produce proteins, hamartin and tuberin, respectively which form a functional heterodimer in the cytoplasm involved in cell signaling and proliferation through the kinase mTOR, the target of rapamycin. Not surprisingly tuberin and hamartin are expressed in the fetal skin, brain and kidney, which give rise to the neoplastic processes seen in TSC. Affected individuals will have a germline mutation in either of these genes with subsequent mutation in the previously normal corresponding allele in the resultant tumor. While statistics vary, TSC1 isinvolved in approximately 20% of cases while TSC2 is involved with approximately 60% with approximately 20% involving an as yet unknown gene(s). TSC2 is more frequently associated with severe phenotypic manifestations and represents a large majority of the de novo mutations.

Renal manifestations are seen in approximately 60% of TSC patients and include cysts and neoplasms, which sometimes lead to renal failure and even death. Henske has proposed that the hamartin-tuberin pathway alters an early renal stem cell which has the potential for both epithelial and mesenchymal differentiation.

Nonneoplastic (Cystic) Lesions in TSC
Renal cysts are a frequent feature in TSC, affecting approximately 45% of affected individuals. These cysts characteristically show tubular epithelial hyperplasia and dysplasia and are believed to represent the precursor lesion for the development of renal cell carcinoma. Cysts are twice as frequent and three times as likely to be multiple in individuals with TSC2 mutations. Prominent cyst formation, which is phenotypically autosomal dominant polycystic kidney disease is seen in 2-3% of TSC cases and corresponds to a large deletion extending from TSC2 into the immediately adjacent PKD1 gene on chromosome 16p. Molecular testing for this large deletion may require alternative forms of molecular testing for its detection.

Neoplastic Lesions
Angiomyolipoma (AML) is the most common renal neoplasm in TSC, being seen in 70-85% of TSC patients. In TSC the sex incidence of AML is equal while in non-TSC AML cases affected females are fourfold as common. AML presents clinically at 25-35 years in TSC, which is 20 years earlier than sporadic cases. These lesions are more likely to be more numerous, multiple and bilateral in patients with TSC2 mutations. Cysts and AML frequently coexist and when sufficiently numerous can cause renal failure.

While usually asymptomatic in TSC patients, as these lesions reach 4 cm in diameter, the vascular component may become aneurysmal resulting in pain with spontaneous rupture and hemorrhage into the calyceal system or retroperitoneum, which may be fatal. Consequently, AMLs are monitored with imaging and embolized or resected when necessary, although recently medical treatment with rapamycin has shown some effect on retarding or stopping growth.

AML is a triphasic benign tumor which is considered a part of the perivascular epithelioid cell tumor or PEComa family. AML is composed of varying proportions of mesenchymal elements--adipose tissue, spindled to epithelioid smooth muscle, and thick-walled blood vessels, with each component showing the same clonal abnormality. Ultrastructurally features of smooth muscle and adipocytes can be seen with intracytoplasmic membrane-bound dense bodies resembling premelanosomes. Immunohistochemically melanocytic markers such as HMB-45 and Melan-A are consistently positive, as are smooth muscle markers such as SMA and MSA. Epithelial markers are consistently negative.

Further complicating the diagnosis of AML are two relatively recently recognized variants. A cystic form of AML, AMLEC (angiomyolipoma with epithelial cysts) has been described with a hobnail epithelium lining cyst walls with a subjacent cellular, mullerian-appearing stroma. The other lesion is malignant epithelioid angiomyolipoma (EAML), an important consideration in the histopathologic differential diagnosis because it mimics renal cell carcinoma. Recognition of EAML has made earlier studies of the incidence of RCC in TSC unreliable and this entity must be excluded clinically. EAML displays sheets of large, ganglion-like cells with abundant eosinophilic or clear cytoplasm and large vesicular nuclei with prominent nucleoli and has little associated adipose component. However, EAML retains the characteristic melanocytic and smooth muscle immunophenotype of AML and does not stain for epithelial markers. Approximately half of EAML cases occur in association with TSC and this lesion is characterized by more infiltrative, aggressive behavior with one-third metastasizing.

Renal cell carcinoma (RCC) occurs in 2-4% of TSC patients. It may be suspected based on its fat-poor imaging and relatively increased growth rate. While clear cell is the most common (75%) phenotype of RCC, chromophobe and papillary types can also be seen. The immunohistochemical profile is positive for epithelial markers like cytokeratin AE1/AE3, CAM 5.2 and EMA and consistently negative for melanocytic and smooth muscle markers. Although the lesion appears histologically identical to the classic type of clear cell RCC, the characteristic mutations of the VHL gene are not found in clear cell RCC from TSC patients, indicating it is a phenocopy with a distinct genetic origin. While TSC2 may be found more commonly in RCC in TSC, an insufficient number of tightly characterized cases have been reported. Of note RCC and AML can co-exist. Clinically, TSC-associated RCC tends to present at an earlier age and has a less aggressive course, although patients can die of metastases. Another common neoplasm which occurs with increased frequency in TSC patients is oncocytoma, which again can be coincident with other renal lesions.

Final Diagnosis and Follow Up
This lesion was diagnosed as: Renal cell carcinoma, clear cell type, 2.5 cm diameter, Fuhrman grade 1, with clear margins and without lymphovascular invasion. The patient did not receive any further therapy and his renal failure has continued.

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