Concordance of MTOR Pathway Mutations and the Diagnosis of Renal Low-Grade Oncocytic Tumor (LOT)

Succinate dehydrogenase deficient renal cell carcinoma frequently expresses GATA3 and L1CAM

Succinate dehydrogenase deficient renal cell carcinoma (SDH RCC) is an uncommon, familial RCC that has overlapping morphologic features with other low grade eosinophilic tumors of the kidney. Although the diagnosis of SDH RCC relies on loss of SDHB by immunohistochemistry (IHC), not all laboratories have access to this antibody. GATA3 and L1CAM are increasingly utilized in the diagnosis of eosinophilic renal tumors; however, their expression profile has not been studied in SDH RCC. We evaluated clinical parameters and GATA3 and L1CAM reactivity in a large nephrectomy cohort (n = 40) of patients with SDH RCC. The male-to-female ratio was 3:1 and the median age was 48 years (range: 17 to 79 years). Specimens included 20 radical resections, 19 partial resections, and 1 unknown procedure. Tumor laterality was nearly equal (right:left = 18:20; one case was bilateral). Tumors in 4 (10%) patients were multifocal. Median tumor size was 2.0 cm (range 1 - 14.8 cm). Tumor stage distribution was: pT1a (n = 16, 40%), pT1b (n = 7, 18%), pT2a (n = 5, 13%), pT2b (n = 4, 10%), pT3a (n = 6, 15%), and pT4 (n = 1, 3%). Most cases (n = 33, 83%) exhibited classical morphologic features, whereas 2/40 (5%) had sarcomatoid differentiation. GATA3 was positive in 37/39 (95%) tumors, with more than 50% of cells positive in 35/37 (95%), and with moderate-high intensity (2/3 +) in 33/37 (89%). L1CAM was expressed in 13/18 (72%) tumors, with moderate-high intensity (2/3 +) in 10/13 (77%). When both markers were performed, dual GATA3/L1CAM expression was present in 12/17 (71%) tumors. As L1CAM has been postulated to represent a marker of principal cell of the distal nephron, frequent L1CAM expression in SDH RCC suggests that they may originate from the principal cells of the distal nephron.

Whole exome sequencing identified mutations of forkhead box I 1 (FOXI1), keratin 6 C (KRT6C) and gap junction protein delta 2 (GJD2) in a low-grade oncocytic tumor of the kidney: a case report

BACKGROUND

Low-grade oncocytic tumor (LOT) of the kidney is an emerging entity among renal oncocytic tumors. While the histological features of LOT of the kidney are similar to those of renal oncocytoma, LOT immunohistochemically expresses keratin 7 (KRT7) but not KIT while renal oncocytoma expresses KIT. Molecular analyses of LOTs of the kidney using next generation sequencing revealed those tumors harbor mutations of mTOR-related genes.

CASE PRESENTATION

An 80-year-old Japanese man with a history of clear cell renal cell carcinoma and prostatic cancer underwent resection of the tumor of the right kidney, 10 mm in diameter, which was monitored for six years. The tumor was histologically composed of oncocytic cells that expressed KRT7, vimentin, SDHA, SDHB and fumarate hydratase, but not KIT, GATA3 and alpha-methylacyl-CoA racemase. We diagnosed the tumor as LOT of the kidney. Whole-exome sequencing of the LOT revealed single nucleotide variants in the DNA-binding region of forkhead box I1 (FOXI1), the coil 1B domain of keratin 6 C (KRT6C) and the intracytoplasmic region of gap junction delta 2 (GJD2), which encodes connexin 36. However, there was no mutations in mTOR-related genes. No copy number alterations were detected in the tumor.

CONCLUSIONS

We report three mutations in genes that have not been previously reported in LOT of the kidney. The genes are not related to the mTOR pathway. Therefore, LOT of the kidney might occur through several mechanisms and/or include several types of renal oncocytic tumors.

Low-grade oncocytic tumor: a review of radiologic and clinical features

PURPOSE

The 2022 World Health Organization classification of renal neoplasia expanded the spectrum of oncocytic neoplasms to encompass newly established and emerging entities; one of the latter is the low-grade oncocytic tumor (LOT). This study reports the radiologic appearance and clinical behavior of LOT.

METHODS

In this IRB-approved, HIPPA-compliant retrospective study, our institution's pathology database was searched for low-grade oncocytic tumors or neoplasms. Patient age, gender, and comorbidities were obtained from a review of electronic medical records, and imaging characteristics of the tumors were assessed through an imaging platform.

RESULTS

The pathology database search yielded 14 tumors in 14 patients. Four patients were excluded, as radiologic images were not available in three, and one did not fulfill diagnostic criteria after pathology re-review. The resulting cohort consisted of 10 tumors (median diameter 2.3 cm, range 0.7-5.1) in 10 patients (median age 68 years, range 53-91, six women). All tumors presented as a solitary, well-circumscribed, mass with solid components. All enhanced as much or almost as much as adjacent renal parenchyma; all but one enhanced heterogeneously. None had lymphadenopathy, venous invasion, or metastatic disease at presentation or at clinical follow-up (median, 22.2 months, range 3.4-71.6). Among five tumors undergoing active surveillance, mean increase in size was 0.4 cm/year at imaging follow-up (median 16.7 months, range 8.9-25.4).

CONCLUSION

LOT, a recently described pathologic entity in the kidney, can be considered in the differential diagnosis of an avidly and typically heterogeneously enhancing solid renal mass in an adult patient.