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Multilocular clear cell renal cell carcinoma is a specifc histologic type listed in the CAP cancer protocol for kidney, but not in the ICD-O-3 and it is not on the list of specific types of renal cell carcinomas in Table 1 of the kidney equivalent terms and definitions in the MP/H manual. There is a malignant multilocular cystic nephroma 8959 in Table 1, but I can't tell if this the same histology as what is stated in this path report.

The partial nephrectomy final diagnosis is renal cell neoplasm. The College of American Pathologists (CAP) Summary lists histology as: multilocular clear cell neoplasm of low malignant potential. The diagnosis comment adds: This neoplasm currently termed multilocular clear cell renal cell neoplasm of low malignant potential (WHO 2016), was previously termed cystic renal cell carcinoma.

The pathology diagnosis reads: Diagnosis Right Kidney, Laparoscopic Nephrectomy: 

-Renal Cell Neoplasm of Oncocytosis (pT1a, pNX See Comment and Template). 

-Surgical margins free of tumor.

Kidney, right, nephrectomy:

Tumor histologic type: Renal cell neoplasms of oncocytosis (see Note)

Sarcomatoid features (%) Not identified

Tumor size: 4 cm (greatest dimension largest tumor)

Other dimensions: 2.7 x 2.5 cm

Macroscopic extent of tumor: Limited to kidney

Focality: Multifocal

Number of tumors: 11 grossly visible, range 0.2 4 cm

Fuhrman grade: 2 of 4

Microscopic extent of tumor:

Perinephric fat invasion: Not identified

Renal sinus invasion: Not identified

Other: N/A

Renal vein involvement: Not identified

Adrenal gland present: No

Involved by tumor: N/A

Direct invasion or metastasis: N/A

Cancer at resection margin: Not identified

Location(s): N/A

Pathologic findings in nonneoplastic kidney: Multiple collections of oncocytic cells

Hilar lymph nodes present: No

Number of involved/number present: N/A

"Thank you for sending this fascinating case. In reviewing the H&E-stained slides, we recognize that multiple lesions of varying sizes are present within the specimen, some with features of oncocytoma, some with those of chromophobe RCC, and yet others with features of both. The immunohistochemical studies for CK7 performed at your institution serve to highlight this point with "mass #1" showing focal single cell staining typical of oncocytoma and "mass #2" showing a patchy and confluent staining pattern typical of chromophobe RCC. This second mass was also positive with special stain for Hales colloidal iron. As mentioned, the morphology varies somewhat in each tumor, however, every single mass is comprised of cells with eosinophilic (pink to bright red) cytopolasm. Some tumors show more tightly nested or sheet like growth, others are more tubular or microcystic. Another important feature, present on slides of renal cortex are microscopic tumorlets seemingly emanating from eosinophilic tubules. This finding, along with the presence of numerous oncocytic neoplasms is supportive of the above diagnosis. The absence of clinical features to suggest Birt-Hogg-Dube syndrome is noted. Although these tumors are not recognized in the current classification of renal tumors, we regard these neoplasms as being a distinct entity, unrelated to both oncocytoma and chromophobe renal cell carcinoma, and have applied the designation "renal tumor of oncocytosis" to such lesions (Gobbo S, et al. Renal cell neoplasms of oncocytosis have distinct morphologic, immunohistochemical, and cytogenetic profiles. Am J Surg Patholl 34:620-626, 2010). We concur that the expected behavior in these cases is one of indolence."

The ICD-O-3.2 Coding Table includes hybrid oncocytic chromophobe tumor as a related term for histology code 8317 (Renal cell carcinoma, chromophobe type). However, this related term is not discussed in the implementation guidelines as being a new term/reportable tumor. The Solid Tumor Rules do not indicate a hybrid oncocytic chromophobe tumor is reportable; however, if a registrar only looked at the ICD-O-3.2 Coding Table, it may seem as though this histology should be collected.

The term hybrid oncocytic chromophobe tumor was not included in the Solid Tumor Rules as a subtype/variant of RCC, or as an equivalent term for chromophobe RCC. There is a SINQ (20180047) that states not to report renal hybrid oncocytic tumor, despite the fact these tumors exhibit mixed features of both oncocytoma and chromophobe RCC. For cases diagnosed 2021 and later, should the clarification in the SINQ apply? Or should the ICD-O-3.2 Coding Table be used which indicates this is a reportable diagnosis? If the standard setters decided not to implement use of hybrid oncocytic chromophobe tumor for 2021, can clarification be added to the Solid Tumor Rules or Implementation Guidelines?

This question was prompted from preparing SEER*Educate coding exercises. We will use the answer as a reference in the rationales.

The 2016 WHO Classification of Tumours of the Urinary System appears to be moving away from using Fuhrman grading toward using WHO/ISUP grade. These seem like similar 4 grade staging systems; however, the SEER Manual specifically states to not use the Special Grade System table for WHO/ISUP. We are seeing the WHO/ISUP grade being used on 2016 pathology reports.

Examples of new grading for renal cell carcinomas

Histologic type: Clear cell renal cell carcinoma

Histologic grade (WHO/ISUP 2016): Grade 3 in a background of 2 (of 4).

And

Histologic type: Clear cell renal cell carcinoma

Histologic grade (ISUP): Grade 2.