Morphological spectrum of renal cell carcinoma, unclassified: an analysis of 136 cases

Abstract

Aims: Renal cell carcinoma, unclassified (RCCU) is a category that includes a morphologically and biologically heterogeneous group of tumours that are unable to be diagnosed as other well-defined entities. We aim to describe the morphological findings of tumours within this category and to determine the most frequent morphological features leading to classification difficulty. Methods and results: One hundred and thirty-six cases of RCCU were examined. Patients ranged in age from 23 to 87 years. Seventy-seven patients were men and 59 were women. International Society of Urological Pathology (ISUP) grade was most commonly 3 (n = 66), followed by 2 (n = 42) and 4 (n = 28). Tumour size ranged from 0.6 to 24.9 cm. The American Joint Committee on Cancer (AJCC) pathological T categories included pT1a (n = 50), pT1b (n = 14), pT2a (n = 7), pT2b (n = 4), pT3a (n = 50) and pT4 (n = 9). Forty-four cases included lymph node(s), 41% of which (n = 18) had metastases. Tumours were assessed for a variety of histological features and assigned to the following morphological groups: predominantly oncocytoma/ chromophobe RCC-like; clear cell RCC-like; papillary RCC-like; collecting duct-like; and pure sarcomatoid differentiation. The majority of the oncocytoma/chromophobe and clear cell RCC-like phenotypes were low stage (pT1 or pT2). The papillary RCC-like, collecting duct-like and pure sarcomatoid phenotypes were mainly high stage (pT3 or pT4). Conclusions: Renal cell carcinoma, unclassified is a term that encompasses tumours with a variety of morphological features and a wide biological spectrum. The most common source of diagnostic difficulty was tumours composed of predominantly eosinophilic cells.

WHO/ISUP classification, grading and pathological staging of renal cell carcinoma: standards and controversies

“…Tumours composed of eosinophilic cells have been shown to cause particular difficulty in classification when they do not show distinctive features [63]. Such tumours are placed in the ‘unclassified’ category.…”

EWSR1 translocation in primary hyalinising clear cell carcinoma of the thymus

“…Rare cases of clear cell renal cell carcinoma may also show a remarkably hypocellular desmoplastic or smooth muscular stroma. 25,26 However, in view of immunohistochemistry and genetics, this differential diagnosis should not pose a problem.…”

Low‐grade oncocytic tumour of kidney (CD117‐negative, cytokeratin 7‐positive): a distinct entity?

“…Diagnosing renal tumours composed of oncocytic cells can often be challenging, because oncocytic morphology is found in a spectrum of entities. It is also currently recognised that there are oncocytic tumours that do not fit into any of the existing ‘oncocytic’ tumour categories . There is a need to define more clearly the morphological and immunohistochemical profiles of such tumours, as well as their genetics and clinical behaviour, in order to determine which tumours truly warrant the designation of carcinoma .…”

“…It is also currently recognised that there are oncocytic tumours that do not fit into any of the existing 'oncocytic' tumour categories. [1][2][3][4] There is a need to define more clearly the morphological and immunohistochemical profiles of such tumours, as well as their genetics and clinical behaviour, in order to determine which tumours truly warrant the designation of carcinoma. 1 A frequent dilemma includes the distinction between the eosinophilic variant of chromophobe RCC (ChrRCC), 5 a malignant tumour, and renal oncocytoma, 6 a benign entity, that can be problematic solely on morphology.…”