Clear cell and papillary renal cell carcinomas in hereditary papillary renal cell carcinoma (HPRCC) syndrome: a case report

Background Hereditary papillary renal cell carcinoma (HPRCC) is a rare autosomal dominant disease characterized by the development of multiple and bilateral papillary type I renal cell carcinomas (RCC) and papillary adenomas caused by activating mutations in the MET proto-oncogene. Classically, distinctive histological features of RCC are described according to the familial renal cell carcinoma syndrome. To date, no clear cell RCC has been reported in HPRCC syndrome. Case presentation We describe the case of a 51-year-old man with a germline MET mutation detected on peripheral blood testing, and no germline VHL mutation, who developed numerous papillary tumors but also unexpectedly clear cell renal cell carcinomas. During the follow-up, an adrenal metastasis was observed 7 years after the initial diagnosis corresponding to a clear cell RCC metastasis. By immunohistochemistry, clear cell tumors showed focal cytokeratin 7, moderate racemase, and diffuse and membranous CAIX expression, while papillary tumors expressed strong diffuse cytokeratin 7 and racemase without CAIX positivity. Using FISH, VHL deletion was observed in one of the clear cell tumors, and the metastatic clear cell tumor presented a trisomy of chromosomes 7 and 17. These last genomic alterations are usually detected in papillary RCC, highlighting the potential link between both histological subtypes of tumors and the HPRCC syndrome. Conclusions The pathologist must be aware that the presence of a non-papillary RCC associated with numerous papillary tumors should not exclude the diagnostic suspicion of HPRCC and thus to perform a thorough genomic study.


Background
It is now estimated that 3% of renal cell carcinomas (RCC) are linked to an inherited predisposition [1]. To date, a dozen of genes involved in autosomal dominant syndromes have been identified, the main ones being: VHL, MET, FLCN, FH, TSC1, TSC2, and SDHB [2]. The most frequent inherited RCC syndrome is von Hippel-Lindau disease with a birth incidence of 1/36,000 caused by germline mutations in the VHL tumor suppressor gene predisposing to the occurrence of clear cell RCC.
Hereditary papillary RCC (HPRCC) is an extremely rare disorder with an estimated incidence of 1/500,000 [3,4]. It is characterized by the development of multiple and bilateral papillary type I RCC and papillary adenomas caused by activating mutations in the MET protooncogene [3]. Familial RCC syndromes are often characterized by bilateral and multifocal tumors in the kidney, generally of the same histological type. Presence of various tumor histological types is a rare event, classically described for Birt-Hogg-Dubé (BHD) syndrome with chromophobe, oncocytic or both components. In this report, we describe for the first time the association between papillary tumors and clear cell RCC in a patient with HPRCC syndrome.

Clinical history
The patient, a 51-year-old man, without a familial background of RCC, underwent computed tomography for hypertension investigation that revealed bilateral and multifocal renal tumors. Initially, eight left partial renal tumorectomies were performed. After this initial surgery, an active surveillance was established for the right kidney by biannual magnetic resonance imaging (MRI) according to the recommendations of the French National Cancer Institute network PREDIR and the local multidisciplinary team meeting (no surgical indication for tumors less than 3 cm in patients with inherited predispositions to RCC except in the case of Hereditary Leiomyomatosis with Renal Cell Cancer).
Two years after initial surgery, the MRI revealed that tumors of the right kidney had grown, and a second surgery was performed on the right kidney with five renal tumorectomies. During the follow-up, the patient Since this date, the stability of the kidney nodules allowed an annual radiological assessment and follow-up without specific therapy.

Pathological findings
The diameters of the 8 tumors of the left kidney ranged from 0.1 cm to 4 cm, and the diameters of the 5 tumors of the right kidney ranged from 0.1 to 2.5 cm. Pathological features are summarized in Table 1. Three nodules measuring respectively 2.5, 3 and 4 cm had typical histological features of clear cell RCC with ISUP grade 1 (Fig. 1c). The other nodules showed typical histological features of papillary tumors, either type 1 papillary RCC (5 tumors) or papillary adenomas often numerous ( Fig.  1a and b). One of the papillary lesions (specimen n°8) was reclassified from renal cell carcinoma to adenoma after reassessment in light of the updated 2016 WHO criteria allowing papillary adenomas to be up to 1.5 cm, with no pseudocapsule [1]. Four nodules with a diameter less than 1.5 cm remained interpreted as papillary renal cell carcinomas due to encapsulation. The left adrenal nodule corresponded to a clear cell RCC metastasis (Fig.  1d).
Considering the presence of different histological types, diagnosis of BHD syndrome was initially suspected and a molecular analysis of FLCN gene was first performed. Absence of germline FLCN mutation led to realize another genetic tests targeting VHL and MET genes. Finally, on peripheral blood testing, a germline MET mutation c.3712G > A, p.(Val1238Ile) was found, but no VHL germline mutation.
An immunohistochemical analysis using TMA and fluorescent in situ hybridization (FISH) analysis were performed on ten representative nodules selected on hematoxylin and eosin-stained sections from the original blocks (2 clear cell carcinomas, 5 papillary carcinomas, 2 papillary adenomas and 1 metastasis) and are summarized in Table 1. Immunohistochemical staining was evaluated according to the percentage of stained cells and the intensity of staining as follows: +, mild; ++, moderate; and +++, intense staining. Fluorescence in situ hybridization (FISH) was performed for VHL loss and gain (trisomy) of chromosome 7 or 17 in the same specimens than immunohistochemical analysis. Deletion of chromosome 3p was assessed using a probe cocktail containing probes to chromosome 3p25.3 and centromere 3 (Z-2084, Zytovision). Chromosomes 7 and 17 gains were assessed using a probe cocktail containing probes to centromere 7 and centromere 17 (Z-2081, Zytovision). For each slide, 50 tumor cell nuclei were scored for probe signals under the fluorescence microscope with × 60 magnification. VHL loss was defined using a cut-off value of 30% of tumor cells with less 3p25.3 signals than centromere 3 signals. Gain of chromosomes 7 and 17 was defined using a cut-off value of 20% of tumor cells with ≥3 centromere 7 and/or 17 signals.
By immunohistochemistry, all papillary lesions were positive for vimentin, cytokeratin 7 (Fig. 2a), and all had stronger labeling for alpha-methylacyl-coA-racemase (p504S) (Fig. 2b). Papillary lesions were uniformly negative for CAIX. Diffuse and membranous CAIX staining (Fig. 3a), and luminal CD10 staining (Fig. 3b) labeled only the 3 clear cell RCC. There was also a focal cytokeratin 7 (Fig. 3c) and moderate racemase (Fig. 3d) expression in clear cell tumors. Using FISH, VHL deletion was observed in only one case corresponding to the clear cell RCC resected in 2010. Trisomy of chromosomes 7 or 17 was encountered in 3 cases of papillary RCC and in the adrenal ccRCC metastasis (Fig. 2c).

Discussion and conclusions
We report for the first time the occurrence of synchronous bilateral kidney tumors of different histological subtypes (clear cell RCC and papillary RCC) in a patient whom the genetic analysis showed the presence of a germline mutation in the MET oncogene, p.(Val1238Ile).
HPRCC is a very rare inherited syndrome characterized by the development of numerous papillary adenomas or papillary type 1 carcinomas [2,5]. Germline mutations within the MET gene were first identified by a genome-wide analysis of HPRCC families then somatic MET mutations were also found in some sporadic papillary type 1 RCC [3,6,7]. The MET proto-oncogene is located on chromosome 7q31 and encodes the receptor for hepatocyte growth factor (HGF). HGF binding to MET results in autophosphorylation of tyrosines in the met kinase domain leading to activation of MAPKinase and PI3K-AKT signal cascades that drive effectors involved in cell proliferation, migration, and invasion [8,9]. In cases of germline MET mutations, there is a ligand-independent constitutive kinase activation [3,10]. Cytogenetic studies showed that the papillary renal carcinomas harboring MET mutations also had trisomy of chromosome 7, resulting from duplication of the chromosome harboring the mutated MET allele [11].
Classically, a specific histological type is described according to each inherited syndrome; for example, clear cell RCC in VHL disease and papillary tumors in HPRC C syndrome. However, recently, two cases of biphasic squamoid RCC (BSARCC) mixed with type 1 papillary RCC have been reported in a familial context of hereditary papillary RCC associated with MET mutation. Immunohistochemical features with expression in both populations of CK7, AMACR and vimentin were consistent with a link between BSARCC and type I papillary RCC [12]. Several hypotheses could be considered to explain the occurrence of various histological types: (1) common metabolic pathway but other cases of mixed histological subtypes should then have been reported; (2) specific histological type according to the type of mutation as described previously for clinical manifestations in VHL disease [13]. Against this possibility, to date, it has not been described any genotype-phenotype correlations in HPRCC. Furthermore, the patient presented one the most frequent MET known mutations. No report has described clear cell RCC or coexistence of other histologic subtypes in the same kidney of a patient with HPRCC except the report of a biphasic squamoid RCC; and (3) both clear cell RCC and papillary RCC are originated from proximal tubules and we can not exclude that additional genetic events of key regulatory genes may push a tumor towards a particular phenotype.
FISH analysis showed trisomy 7 and/or 17 in 3 out of 4 tested cases of papillary RCC and more unexpectedly in the clear cell RCC metastasis. This data would be in favor of a molecular link between both histological subtypes. Trisomy 7 and/or 17 were not observed in the papillary adenomas, perhaps influenced by difficulty evaluating sufficient numbers of tumor cells in microscopic papillary adenomas and a potential lower rate of these alterations in adenomas compared to papillary carcinomas. Interestingly, among the 3 clear cell RCC, VHL deletion was observed in only one case.
In summary, it is important to remember that some genomic alterations might be associated with synchronous bilateral kidney tumors with different histological types. The pathologist must be aware that the presence of a non-papillary RCC associated with numerous papillary adenomas or type I carcinomas should not exclude the diagnostic suspicion of HPRCC and thus to perform a thorough genomic study.