OSU Department of Pathology

Anatomical Pathology Interesting Case Conference

Microscopic Description:

Histology revealed two distinct morphologies (see black and red arrow).

1. Black arrow: sheets of polygonal cells with eccentric nuclei, clear cytoplasm and well –defined cell membrane, interspersed with branching network of vascular tissue.

2. Red arrow: Eosinophilic bone matrix with small cells having flattened nuclei.

Immunohistochemical stains show positive staining for PAX8, AE1/3 and negative for CK-7.

Discussion:

Renal Cell Carcinoma may be associated with calcifications but osseous metaplasia or heterotopic bone formation is an extremely rare finding. True osseous metaplasia is a benign and non-neoplastic with no nuclear atypia, mitotic figures and negative epithelial markers.

The exact mechanism underlying bone formation in RCC is unclear, but it has been proposed that tumor cell triggered by ischemia, necrosis and chronic inflammation, promote osteogenic differentiation and ectopic bone formation.

Grossly, if it is large and visible to the naked-eye, the cut surface appears white, stony-hard foci intermixed with the tumor tissue.

Microscopically, it shows eosinophilic bony trabeculae (Interlacing spicules of lamellar or woven bone tissue), lacunae containing osteocytes which are surrounded by dense hyaline or fibrous stroma**

RCC and osseous metaplasia (incidental finding) are managed together with Nephrectomy. The prognostic implications of osseous metaplasia in RCC is not well-established. However, early-stage has a favorable prognosis and a small subset are associated with high-grade tumors and poorer clinical outcomes, with an estimated 5-year survival rate of approximately 77%.

References:

Cakici MC, Kır G, Akalın MK, Yıldırım A. Clear cell renal cell carcinoma with osseous metaplasia: Two extremely rare cases and review of the literature. Arch Esp Urol. 2020 Sep;73(7):651-654.

Agarwal S, Bohara S, Jha R, Khurana N, Agarwal PN. Clear cell renal cell carcinoma with osseous metaplasia: Rare case report. J Cancer Res Ther. 2015 Oct-Dec;11(4):1039. doi: 10.4103/0973-1482.146109.

 

Pan H, Wu D, Wang H, Pan Y, Zhang T, Zhou J. Clear Cell Renal Cell Carcinoma With Extensive Osseous Metaplasia: Report of a Rare Case. Urology. 2017 Jul;105:e3-e5. doi: 10.1016/j.urology.2017.02.048.

N Agha, G Dimuth. Osseous metaplasia in a case of clear cell renal cell carcinoma: a case report and literature review. Pathology. 2024 February,56(1): S44-45.

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