cow-2022-19

a) Clear cell renal cell carcinoma with sarcomatoid differentiation

b) Mucinous tubular and spindle cell carcinoma

c) Collision tumor (clear cell renal cell carcinoma and angiomyolipoma)

d) Clear cell renal cell carcinoma with low grade spindle cell proliferation

1. d

1. Clear cell renal cell carcinoma with low grade spindle cell proliferation. 

The main differential diagnosis includes clear cell RCC with sarcomatoid differentiation (WHO/ISUP grade 4 by definition, with well-known poor prognosis even when focal in extent) versus clear cell RCC with admixed low grade spindle cells. This distinction is effectively a morphologic one (IHC performed in this case did show spindled cells with similar CAIX+/PAX8+/CK7- immunoprofile to adjacent traditional clear cell RCC component). The lack of high grade features within the spindled element (no marked nuclear pleomorphism, necrosis, or increased mitotic activity) points towads a diagnosis of “low grade spindle cell proliferation” of the adjacent low grade RCC rather than bonefide sarcomatoid differentiation.

A simple concept has been described in papillary RCC (1). The concept of “focal spindle morphology” was first elucidated in 2001 by de Peralta-Venturina, proposing that these should not be considered as sarcomatoid differentiation (2). In 2007, Delahunt et al. depicted “early spindle cell change” in clear cell RCC, and suggested this could be a precursor to sarcomatoid differentiation (3). However, a more recent study by Isikci et al suggested that based on outcome data, low grade spindle cell proliferation in clear cell RCC is unlikely to be an initial step in sarcomatoid differentiation (4).

1. Argani P, Netto GJ, Parwani AV. Papillary renal cell carcinoma with low-grade spindle cell foci: a mimic of mucinous tubular and spindle cell carcinoma. Am J Surg Pathol. 2008 Sep;32(9):1353-9.

2. de Peralta-Venturina M, Moch H, Amin M, Tamboli P, Hailemariam S, Mihatsch M, Javidan J, Stricker H, Ro JY, Amin MB. Sarcomatoid differentiation in renal cell carcinoma: a study of 101 cases. Am J Surg Pathol. 2001 Mar;25(3):275-84.

3. Delahunt B, Bethwaite PB, McCredie MR, Nacey JN. The evolution of collagen expression in sarcomatoid renal cell carcinoma. Hum Pathol. 2007 Sep;38(9):1372-7.

4. Tanas Isikci O, He H, Grossmann P, Alaghehbandan R, Ulamec M, Michalova K, Pivovarcikova K, Montiel DP, Ondic O, Daum O, Prochazkova K, Hora M, Michal M, Hes O. Low-grade spindle cell proliferation in clear cell renal cell carcinoma is unlikely to be an initial step in sarcomatoid differentiation. Histopathology. 2018 Apr;72(5):804-813.

Ankur Sangoi
El Camino Hospital, Mountain View, CA

Kidney

Clear cell renal cell carcinoma; kidney; low-grade spindle cells.