Contributed by Fawaz Almutairi, MD, Shikha Malhotra, MD and Gabriela Quiroga-Garza, MD
The patient is a female in her 50s who presents with asymptomatic, incidentally detected renal mass. Personal history is relevant for low-grade appendiceal mucinous neoplasm (LAMN, pTis), and family history of ovarian and gastric cancer. Smoking history is negative. CT scan and MRI of abdomen demonstrate a left lower renal pole enhancing lesion (2.0 cm). The patient elects to undergo a laparoscopic partial nephrectomy of the mass, instead of active surveillance or percutaneous biopsy/ cryoablation.
The partial nephrectomy specimen consists of an ovoid segment of enucleated renal tissue (1.8 x 1.7 x 1.5 cm) with a scant rim of apparent normal parenchyma, along with a separate segment of membranous, presumed renal capsule. The cut surface shows a homogeneous, solid, pale yellow mass with no evident necrosis (Figure 3). The lesion is less than 1-mm away from the parenchymal resection margin.
Histologic examination demonstrates a well-circumscribed renal epithelial neoplasm with compact papillary architecture, composed of a dual-cell population of (predominant) small basophilic cells closely intermixed with large eosinophilic squamoid cells (approximately 10-15% of the tumor volume) (Figure 4A and 4B). Emperipolesis is present within the large squamoid cells and scattered foamy histiocytes are noted throughout the tumor. No necrosis, increased mitoses or lymphovascular invasion are identified. The tumor is confined within the kidney.
Immunohistochemical stains demonstrate the tumor cells are positive for PAX8, Vimentin, CK7, CD57 and P504S, and negative for CA9, WT1, CD10, Cathepsin K and HMB45. Cyclin D1 is expressed only in the larger squamoid cells and Fumarate hydratase immunostain shows retained expression in all cells (Figure 5A, 5C and 5C).
Fluorescent in-situ hybridization (FISH) analysis show trisomy of chromosome 17 in approximately 48% of the tumor cells.