Case Report: Multifocal biphasic squamoid alveolar renal cell carcinoma

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. The post-surgery period did not show any clinical complications. The patient was asymptomatic and free of disease at the last contact, 6 months after diagnosis.

Figure 1.

CT scans show multiple tumors in the right kidney (A and B). Gross examination displays a yellowish central tumor with solid-cystic areas corresponding to a clear cell renal cell carcinoma (C) and four peripheral whitish tumors and several intrarenal micronodules corresponding to biphasic squamoid alveolar renal cell carcinomas (C and D).

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. On low-power 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. True squamous cell differentiation, however, was not observed. Mitosis and necrosis were not seen.

Figure 2.

Panoramic view of one of the biphasic squamoid alveolar renal cell carcinomas displaying a conventional type 1 papillary renal cell carcinoma component (A). Alveolar structures filled with large cells are typical of biphasic squamoid alveolar renal cell carcinoma (B).

Figure 3. Microscopic detail of the alveolar structures containing small groups and single large squamoid cells positive for cyclin D1.

By immunohistochemistry, the tumor was positive with CK7, vimentin, PAX-8, racemase, RCC marker, AE1/AE3, 34βE12, carbonic anhydrase IX, CD10, and cyclin D1. 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.

Discussion

BSARCC is a recently recognized variant of renal carcinoma^1,2. Its pathological diagnosis can be suggested on hematoxylin-eosin slides and is based on the recognition of two different cell types arranged in a distinct architecture. Small groups of large cells with abundant cytoplasm and squamoid appearance are surrounded by small cells with scant cytoplasm forming alveolar-like structures. This distinct growth pattern can be more or less evident in different tumor areas and, same as happens in the case here presented, can be combined with areas of conventional PRCC². The combination of BSARCC and PRCC histologies in almost half of the previously published cases favors the inclusion of this tumor within the broad spectrum of PRCC². No association of BSARCC with CCRCC, as in the case here presented, has been reported so far.

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, interestingly, cyclin D1. Cyclin D1 immunostaining is specific of this tumor and helps in its recognition in daily practice. Interestingly, Cyclin D1 immunostaining is restricted to the centrally located squamoid cells. Molecular-genetic data show gains of chromosomes 7 and 17, thus linking BSARCC to PRCC.

Consent

Written informed consent was obtained from the patient for publication of this case report and any accompanying images and/or other details that could potentially reveal the patient’s identity.