[Clinicopathological characteristics of high-grade succinate dehydrogenase-deficient renal cell carcinoma]

Objective: To investigate the clinicopathological characteristics and diagnosis of high-grade succinate dehydrogenase-deficient renal cell carcinoma (SDH-RCC). Methods: Three cases of high-grade SDH-RCC diagnosed by immunohistochemical staining and/or molecular testing were collected from Affiliated Hospital of Qingdao University and 971 Hospital of Navy of Chinese People's Liberation Army from January 2015 to December 2023. The clinicopathological characteristics and immunohistochemical features were summarized using light microscopy. Two cases were tested for gene mutations by next-generation sequencing. Results: Of the 3 cases, 2 were male and 1 was female. The ages were 49, 61, and 53 years, respectively. Gross examination revealed that all tumors were single nodules with diameters of 7.0, 4.5, and 5.2 cm, respectively, grayish white in color with irregular borders. Cases 1 and 2 exhibited solid cut sections, whereas case 3 had cystic and solid cut sections. Microscopically, all cases had high WHO/ISUP nuclear grade (3 or 4) and overt invasion. Case 1 exhibited a solid, sheet-like growth pattern with numerous scattered glandular ducts or acinar structures. Case 2 displayed a diffusely growth pattern reminiscent of sarcoma. Case 3 demonstrated intracystic papillary and nodular infiltrative growth patterns. Large clear cytoplasmic vacuoles could be observed in the focal areas of case 1 and case 3. Prominent peritumoral lymphocytes in stroma were noted in case 1. Case 1 was diagnosed with regional lymph node metastasis, and case 2 was diagnosed with renal vein thrombosis. Immunohistochemical staining revealed that SDHB and SDHA were deficiently expressed in 3 cases, while PAX8, FH, and INI-1 exhibited diffuse expression. CD10 (1/3), CA9 (1/3), and CK20 (1/3) were occasionally expressed. The Ki-67 proliferation index ranged from 10% to 50%. Two cases underwent next-generation sequencing and were both found to harbor pathogenic mutations in SDHA (case 2 had a frameshift mutation, and case 3 had a splice site mutation). All 3 cases were followed up for 11 to 112 months. Case 2 died 11 months post-operation, while case 1 and case 3 survived for 19 and 112 months, respectively, without any recurrence or metastasis. Conclusions: High-grade SDH-RCC is a rare subtype of SDH-RCC. The tumor exhibits various architectural patterns and is often misdiagnosed as other types of renal cell carcinoma. The presence of cytoplasmic vacuoles may be indicative for diagnosis. Compared to typical SDH-RCC, the high-grade subtype generally shows a larger tumor size, higher TNM stage, greater invasive potential, and poorer prognosis. For high-grade SDH-RCC, routine SDHB immunohistochemical staining may be necessary. The occurrence of high-grade SDH-RCC may be associated with mutations in SDHA.