Case Report: Multifocal biphasic squamoid alveolar renal cell carcinoma

A multifocal biphasic squamoid alveolar renal cell carcinoma in a 68-year-old man is reported. Four different peripheral tumor nodules were identified on gross examination. A fifth central tumor corresponded to a conventional clear cell renal cell carcinoma. Biphasic squamoid alveolar renal cell carcinoma is a rare tumor that has been very recently characterized as a distinct histotype within the spectrum of papillary renal cell carcinoma. Immunostaining with cyclin D1 seems to be specific of this tumor subtype. This is the first reported case with multifocal presentation.


Introduction
The so-called biphasic squamoid alveolar renal cell carcinoma (BSARCC) was described for the first time in 2012 by Petersson et al. 1 and has been very recently revisited and fully characterized by Hes et al. 2 . Histological, immunohistochemical, comparative genomic hybridization and fluorescence in situ hybridization analyses have revealed that BSARCC is a renal neoplasm closely related to papillary renal cell carcinoma (PRCC) 2 .
The present paper describes a new BSARCC with multifocal presentation that was associated with a conventional clear cell renal cell carcinoma (CCRCC). To note, multifocality has not been reported in BSARCC so far.

Case report
A 68-year-old man presented with transient hematuria. CT scan revealed multiple tumors on his right kidney, four of them being located at the periphery ( Figure 1). Radical nephrectomy was performed. Post-surgery period did not show any clinical complication. The patient is asymptomatic and free of disease at the last contact, 6 months after diagnosis.
On gross examination up to five tumors and several small intrarenal micronodules were discovered ( Figure 1). Four tumors were subcapsular and showed a whitish homogeneous cut surface, measuring between 1 and 3 cm in diameter. The fifth tumor was centrally located, presented mixed solid and cystic areas with a yellowish cut surface and measured 4.5 cm in diameter.
Histologically, the yellowish central tumor was a conventional organ-confined CCRCC grade 1 (ISUP 2013) 3 ( Figure 2). On lowpower view, all the whitish peripheral tumors and the micronodules displayed a similar histology consisting in areas reminiscent to glomerular-like structures ( Figure 2 and Figure 3) alternating with others typical of type 1 PRCC. On high magnification, these structures were composed of a single row of small cells with scant cytoplasm displaying an alveolar disposition. The alveoli were filled with cell groups with large cytoplasm and squamoid appearance ( Figure 3). True squamous cell differentiation, however, was not observed. Mitosis and necrosis were not seen.
By immunohistochemistry (Figure 4), the tumor was positive with CK7, vimentin, PAX-8, racemase, RCC marker, AE1/AE3, 34βE12, carbonic anhydrase IX, CD10, and cyclin D1 (SP4-R clone, Ventana, USA). Immunostaining pattern was distinct depending on the cell type. For instance, cyclin D1 and 34βE12 immunostained selectively the squamoid cells whilst RCC marker and carbonic anhydrase IX did it only in small alveoli-forming cells. The rest of the antibodies immunostained both cell types. The tumor was negative with p63 and CK20.

Amendments from Version 1
The new version takes into consideration all the reviewers's comments and clarify a misunderstanding in the text. On one hand, figures have been modified, as requested, to highlight the squamoid cell nests and to give a more detailed approach to the immunohistochemical profile of the tumor. On the other, the distinct distribution of the cyclin D1 along the tumor has been detailed. In fact, cyclin D1 immunostaining was restricted specifically to the squamoid cells, a point that was not clear in the former version. Finally, some references supporting that cyclin D1 can also be detected in other renal neoplasms have been included in the reference list.  Morphological diagnostic features of BSARCC can be supported by immunohistochemistry and, if necessary, by genetics. All BSARCC reported to date are positive with cytokeratin 7, epithelial membrane antigen, vimentin and cyclin D1. To note, cyclin D1 shows a selective immunostaining restricted to the central squamoid cell groups. This distinct cyclin D1 distribution seems to be specific of this tumor and may be of help in its recognition. This marker, however, can also immunostain other renal cell neoplasms, as recently reported 4-6 . Molecular-genetic data show gains of chromosomes 7 and 17, thus linking BSARCC to PRCC. labelling for cyclin D1 has been reported in clear cell renal cell carcinoma, papillary renal cell carcinoma, chromophobe renal cell carcinoma and oncocytoma (1, 2) and more recently in clear cell papillary renal cell carcinoma (3) and SDH-deficient renal cell carcinoma (4). Since the immunoreactivity might depend of the clone used, the Author should supply information regarding the antibody to cyclin D1. It would be also interesting to know whether cyclin D1 is positive in the clear cell renal cell carcinoma. Finally, pictures of clear cell renal carcinoma and more detailed pictures demonstrating the squamoid features of biphasic squamoid alveolar renal cell carcinoma should be added.
We have read this submission. We believe that we have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however we have significant reservations, as outlined above.
No competing interests were disclosed. Competing Interests: