The WHO 2022 Classification of Renal Neoplasms (5th Edition): Salient Updates

The first categorization for renal tumours was made by the WHO in 1981 and included only renal cell carcinoma (RCC). After that, classification was continuously altered over five decades. The WHO 2022 Classification of Urinary and Male Genital Tumours 2022 (5th edition) is molecular-driven and contains major revisions compared to the earlier classification from 2016. This revised edition divided renal tumours into four major broad categories: clear cell renal tumours, papillary renal cell tumours, oncocytic and chromophobe renal tumours, and collecting duct tumours. 'Other renal tumours' and 'molecularly defined renal carcinomas' are two other categories that were also included. Transcription factor binding to IGHM enhancer 3 (TFE3)-rearranged, TFEB-altered, elongin C (ELOC)-mutated (formerly TCEB1)-mutated, fumarate hydratase (FH)-deficient, succinate dehydrogenase (SDH)-deficient, anaplastic lymphoma kinase (ALK)-rearranged, and SWI/SNF-related matrix-associated actin-dependent regulator of chromatin subfamily B member 1 (SMARCB1)-deficient renal cell carcinomas are molecularly defined entities. Eosinophilic vacuolated tumours and low-grade oncocytic tumours are classified as emerging entities. Molecularly characterized renal tumours include those with SMARCB1 deficiencies, TFE3 rearrangements, TFEB alterations, ALK rearrangements, ELOC mutations, etc. Thyroid-like follicular carcinoma, eosinophilic vacuolated tumour, and low-grade oncocytic tumour are a few emerging entities of renal tumours. Improved therapy targets for each kidney tumour can be achieved using immunohistochemistry (IHC) and molecular definition updates. This study aims to highlight new developments in the WHO 2022 categorization of renal tumours with regard to diagnostic, morphological, molecular, IHC, clinical, and prognostic updates.

Low-grade oncocytic tumour of the kidney is characterised by genetic alterations of TSC1, TSC2, MTOR or PIK3CA and consistent GATA3 positivity

Low-grade oncocytic tumour (LOT) of the kidney has recently emerged as a potential novel tumour type. Despite similarity to oncocytoma or eosinophilic chromophobe renal cell carcinoma, it shows diffuse keratin 7 immunohistochemistry (IHC) and negative KIT (CD117), which differs from both. We aimed to identify the molecular characteristics of these tumours. Seventeen tumours (one male, 16 female, nine previously published) fitting the original description of this entity (solid eosinophilic cell morphology, often with areas of tumour cells loosely stretched in oedematous stroma, and the above IHC features) were analysed with a next-generation sequencing panel of 324 cancer-associated genes from formalin-fixed, paraffin-embedded tissue. All tumours harboured at least one alteration in either TSC1 (n = 7, 41%), TSC2 (n = 2, 12%), MTOR (n = 5, 29%) or PIK3CA (n = 4, 24%). Four tumours harboured a second alteration, including two NF2, one each in conjunction with MTOR and TSC2 alterations, one PTEN with TSC1 alteration and one tumour with both MTOR and TSC1 alterations. No other renal cancer-related or recurring gene alterations were identified. In addition to the previously described IHC findings, 16 of 16 were positive for GATA3. Eleven patients with follow-up had no metastases or recurrent tumours. Recurrent tuberous sclerosis/MTOR pathway gene alterations in LOT support its consideration as a distinct morphological, immunohistochemical and genetic entity. PIK3CA is another pathway member that may be altered in these tumours. Further study will be necessary to determine whether tumour behaviour or syndromic associations differ from those of oncocytoma and chromophobe carcinoma, warranting different clinical consideration.

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

AIM

To describe a group of distinct low-grade oncocytic renal tumours that demonstrate CD117 negative/cytokeratin (CK) 7-positive immunoprofile.

METHODS AND RESULTS

We identified 28 such tumours from four large renal tumour archives. We performed immunohistochemistry for: CK7, CD117, PAX8, CD10, AMACR, e-cadherin, CK20, CA9, AE1/AE3, vimentin, BerEP4, MOC31, CK5/6, p63, HMB45, melan A, CD15 and FH. In 14 cases we performed array CGH, with a successful result in nine cases. Median patient age was 66 years (range 49-78 years) with a male-to-female ratio of 1:1.8. Median tumour size was 3 cm (range 1.1-13.5 cm). All were single tumours, solid and tan-brown, without a syndromic association. On microscopy, all cases showed solid and compact nested growth. There were frequent areas of oedematous stroma with loosely arranged cells. The tumour cells had oncocytic cytoplasm with uniformly round to oval nuclei, but without significant irregularities, and showed only focal perinuclear halos. Negative CD117 and positive CK7 reactivity were present in all cases (in two cases there was focal and very weak CD117 reactivity). Uniform reactivity was found for PAX8, AE1/AE3, e-cadherin, BerEP4 and MOC31. Negative stains included CA9, CK20, vimentin, CK5/6, p63, HMB45, Melan A and CD15. CD10 and AMACR were either negative or focally positive; FH was retained. On array CGH, there were frequent deletions at 19p13.3 (seven of nine), 1p36.33 (five of nine) and 19q13.11 (four of nine); disomic status was found in two of nine cases. On follow-up (mean 31.8 months, range 1-118), all patients were alive with no disease progression.

CONCLUSION

Low-grade oncocytic tumours that are CD117-negative/CK7-positive demonstrate consistent and readily recognisable morphology, immunoprofile and indolent behaviour.