Objective To investigate the clinicopathological features, immunophenotypes, molecular genetic alterations, and prognosis of succinate dehydrogenase-deficient renal cell carcinoma (SDH-RCC).

Methods A total of 11 cases of SDH-RCC diagnosed at West China Hospital, Sichuan University between 2016 and 2023 were selected for clinicopathological, immunohistochemical, and DNA sequencing analyses.

Results Among the 11 cases of SDH-RCC, there were 5 male patients and 6 female patients. The patients' ages ranged from 12 to 71 years, with an average age of 39.7 years. Among them, 5 patients had tumors located in the right kidney, 5 had tumors located in the left kidney, and 1 patient had bilateral tumors. Microscopic observation showed that the tumor cells of the SDH-RCC patients displayed a wide spectrum of structures, forming sheet-like, nested, and glandular structures. In addition, tumor cells in papillary structures were observed in some cases. The tumor cells had abundant cytoplasm, was eosinophilic, and contained flocculent materials. Intracytoplasmic vacuolations were observed in some of the cells. Among all the patients, 7 (7/11, 63.6%) showed typical low-grade features (grade 1-2 according to the International Society of Urological Pathology ISUP/WHO 2016 classification), and 4 (4/11, 36.4%) showed high-grade features (grade 3 according to the ISUP/WHO 2016 classification). The average ages of patients with low-grade and high-grade features were 32.1 years and 58.0 years, respectively. Immunohistochemical staining of all 11 cases demonstrated negative results for SDHB and cytokeratin 7 (CK7), and positive staining results for paired box 8 (PAX-8), fumarate hydratase (FH), and epithelial membrane antigen (EMA). Their Ki-67 index was 1%-30%. In one case, the loss of SDHB expression was also accompanied by a loss of SDHA expression. Sanger sequencing was performed to examine all the exons of SDHB in 7 cases. One case showed a frameshift mutation, c.236Tdel (p.K80Rfs*), and another case harbored a missense mutation, c.725G>A (p.Arg242His). In another case, next generation sequencing revealed that large fragments of SDHB (Exon 4-8 del) were missing. Follow-up data were available for 10 patients. The follow-up time ranged from 4 to 138 months, with the average being 32.8 months, and all patients survived. Metastasis and recurrence were reported in 5 cases, with 3 of them showing high-grade features and 2 showing low-grade features.

Conclusion SDH-RCC is rare and the patients demonstrate a relatively young age of onsets. Patients may present with bilateral tumors. Tumors with low-grade features usually occur in young patients, with their Ki-67 index usually being lower than 5%. Individual cases may experience tumor recurrence and metastasis over a long period of follow-up. Tumors with high-grade features tend to occur in older patients who have a higher Ki-67 index, and who are prone to recurrence and metastasis. Negative immunohistochemical staining results for SDHB can assist in tumor diagnosis, but the loss of SDHB protein expression does not necessarily lead to the detection of SDHB gene mutation.