Kidney tumor

• Use of multilocular cystic renal cell carcinoma is considered obsolete (WHO 2016); some literature references in this topic use the older terminology

• 90% are discovered incidentally, on radiology for other purposes
• Asymptomatic in > 80% of cases
• Up to 20% of patients present with symptoms such as hypertension, hematuria, a palpable mass, flank or abdominal pain but not the classic renal cell carcinoma (RCC) triad of gross hematuria, pain and a palpable mass
• References: J Cancer Res Clin Oncol 2008;134:433, Histol Histopathol 2012;27:969, Am J Surg Pathol 2013;37:1469, Virchows Arch 2018;473:85, Clin Genitourin Cancer 2016;14:e553

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Contributed by Maria Tretiakova, M.D., Ph.D.

Contributed by Maria Tretiakova, M.D., Ph.D. and @ahmsab_MD on Twitter

Which of the following is true about this encapsulated multilocular cystic renal tumor with clear cell morphology?

1. Does not require surgical treatment
2. Frequently progresses to conventional clear cell renal cell carcinoma (CCRCC)
3. Necrosis, solid growth and invasion are not allowed for this diagnosis
4. Often associated with acquired cystic kidney disease
5. VHL mutation or 3p loss are highly unlikely

C. Necrosis, solid growth and invasion are not allowed for this diagnosis. Multilocular cystic renal neoplasm of low malignant potential (MCNLMP) has been excluded from the renal cell carcinoma category due to its uniformly good outcomes and has been renamed in the 2016 World Health Organization Classification. Histologically MCNLMP has pure cystic architecture and is composed of clear cells (similar to conventional CCRCC) but these cells are aligned in a single layer and do not form solid expansile nodules or tumor nests. Presence of necrosis, brisk or atypical mitoses, lymphovascular or fat invasion, sarcomatoid or rhabdoid dedifferentiation are incompatible with this diagnostic entity (C). However, despite its indolent behavior, MCNLMP is still treated surgically due to complex cystic morphology by radiologic imaging (Bosniak IIF - IV) (A). Immunostaining and molecular findings are similar to conventional CCRCC; VHL gene alteration due to mutation or 3p loss was documented in the majority of studied cases (E). Because of these similarities, there is a concept that MCNLMP, cystic CCRCC and conventional RCC represent a continuum of pathogenetic development with MCNLMP representing the most indolent end of tumor spectrum; however, no documented cases of actual MCNLMP progression to CCRCC have been reported (B). There is no known association between MCNLMP and acquired cystic kidney disease (D).

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Reference: Multilocular cystic renal neoplasm of low malignant potential

What immunohistochemical profile is most consistent with multilocular cystic renal neoplasm of low malignant potential (MCNLMP)?

1. CAIX+, CK7 variable, CD10+, RCC+
2. CAIX+, CK7+, HMWCK+, GATA3+
3. CAIX+, CK7-, TFE3+, vimentin+
4. CAIX-, TFE3+, cathepsin K+, MelanA+

A. CAIX+, CK7 variable, CD10+, RCC+. Immunostaining is rarely needed for establishing MCNLMP diagnosis, which is primarily based on morphologic assessment; however, if IHC is performed in an MCNLMP case, the expected immunoprofile will be diffuse expression of CAIX and CD10, as well as variable expression of CK7 and RCC (A). Coexpression of CAIX / CK7 plus variable expression of HMWCK and GATA3 are typically seen in clear cell papillary renal cell tumor (B). Conventional clear cell RCC could be distinguished from TFE3 rearranged RCC with panel results C and D, respectively.

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Reference: Multilocular cystic renal neoplasm of low malignant potential