Review: Updates in Histologic Grading of Urologic Neoplasms

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Recommendations for histologic grading of neoplasms change over time as research provides new insights into tumor biology and behavior. In the case of urologic tumors, the major guidance comes from the World Health Organization (WHO), often in conjunction with the International Society of Urological Pathology (ISUP).

In Archives of Pathology and Laboratory Medicine, Travis Rice-Stitt, MD, former fellow in the Massachusetts General Hospital Department of Pathology, Chin-Lee Wu, MD, PhD, associate pathologist and director of Genitourinary Pathology Services at Mass General and the Mass General Cancer Center, and colleagues reviewed the history of histologic grading of certain urologic cancers. This summary reports the most recent updates.

Renal Cell Carcinoma

Clear cell and papillary renal cell carcinoma (RCC)—The 2016 WHO/ISUP system was adopted by the 2017 Cancer Staging Manual of the American Joint Committee on Cancer. Both nucleolar prominence and eosinophilia of the nucleoli are now considered:

• Grade 1—Nucleoli that are absent or inconspicuous and basophilic at ×400 magnification
• Grade 2—Nucleoli that are conspicuous and eosinophilic at ×400 and visible but not prominent at ×100
• Grade 3—Nucleoli that are conspicuous and eosinophilic at ×100
• Grade 4—Severe nuclear pleomorphism, multinucleated giant cells, rhabdoid and/or sarcomatoid differentiation

Chromophobe RCC should not be graded: Although it has inherent nuclear pleomorphism, it has a more favorable prognosis than other RCC subtypes. There are no formal guidelines for grading of other subtypes.

Rhabdoid or sarcomatoid differentiation can be associated with numerous RCC subtypes. It should be reported as present or absent. In the rare circumstances that a neoplasm has purely rhabdoid or sarcomatoid morphology, it is best termed "RCC unclassified with a [rhabdoid/sarcomatoid] component."

Tumor necrosis is an important indicator of poor prognosis in clear cell RCC. It should be reported as present or absent, and if present both the macroscopic and microscopic percentage of necrosis should be noted.

Prostate Adenocarcinoma

After reviewing the 2014 ISUP modifications to Gleason scores, the authors explain the ISUP grade groups, adopted by the WHO in 2016. These simplify the 25 possible Gleason variations into five prognostically significant categories:

• Grade group (GG)1 (best overall prognosis)—Gleason scores ≤6
• GG2—Gleason 3+4
• GG3—Gleason 4+3
• GG4—Gleason 8 (3+5, 5+3 or 4+4)
• GG5—Gleason 9 and 10 (4+5, 5+4 or 5+5)

The review gives detail about what features to report for prostate biopsy and resection specimens.

Urothelial Neoplasms

The 2016 WHO classification system for urothelial neoplasms preserves the 2004 WHO scheme:

• Papilloma
• Papillary urothelial neoplasm of low malignant potential
• Low-grade urothelial carcinoma (LGUC)
• High-grade urothelial carcinoma (HGUC)

Grading is most important in noninvasive disease, which should be reported as such. pTa and PT1 tumors may be either LGUC or HGUC, but most pT2 tumors are HGUC by default.

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