Prevalence and morphology of SDHB-negative GISTs: insights from a Tanzanian tertiary center

Gastrointestinal stromal tumors (GISTs) in sub-Saharan African countries, including Tanzania, have been poorly researched in terms of their prevalence, histomorphological features, clinical presentation and response to targeted therapy. SDHB-negative GISTs, a subset of GISTs is easily diagnosed by using immunohistochemistry (IHC) and can be treated with second-line tyrosine kinase inhibitors targeted therapy when appropriate. This study aimed at determining the frequency and histomorphological features of CD117 positive SDHB-negative GISTs and their associated factors at Muhimbili National Hospital (MNH) This was a retrospective cross-sectional study conducted at MNH-Central Pathology Laboratory. Archived FFPE blocks of CD117 positive GISTs diagnosed between January 2015 and January 2022 were included. Data was extracted from patients’ records using a designed spreadsheet with all relevant study variables. Data analysis was conducted using SPSS version 23, and Fisher’s exact test was used to assess associations between categorical variables such as age, gender, histomorphological features, and tumor location. A p-value of <0.05 was considered statistically significant. A total of 60 CD117-positive GISTs were analyzed following SDHB immunohistochemical testing. The age range was 30–87 years, with a mean age of 54.37 ± 14.6 years. Among the 60 evaluable cases, 12 (20.0%; 95% CI, 11.8–31.8%) were SDHB-negative. SDHB negativity was observed in 5 of 24 (20.8%; 95% CI, 9.2–40.5%) cases occurring in patients aged ≤50 years and 7 of 36 (19.4%; 95% CI, 9.8–35.0%) cases occurring in patients aged >50 years. SDHB negativity was identified in 6 of 36 (16.7%; 95% CI, 7.9–31.9%) male patients and 6 of 24 (25.0%; 95% CI, 12.0–44.9%) female patients. Spindle-cell morphology was associated with SDHB negativity in 8 of 36 (22.2%; 95% CI, 11.7–38.1%) cases, compared with 4 of 24 (16.7%; 95% CI, 6.7–35.9%) cases with mixed epithelioid/spindle-cell morphology. By anatomical site, SDHB negativity was observed in 7 of 34 (20.6%; 95% CI, 10.3–36.8%) gastric GISTs and 3 of 12 (25.0%; 95% CI, 8.9–53.2%) small-bowel GISTs. No statistically significant associations were identified between SDHB status and age, sex, anatomical site, or histomorphological pattern. SDHB-negative GISTs accounted for 20.0% of the evaluable cases in this study. While we observed a higher numerical trend for age, sex, anatomical site and histomorphology, limited sample size precluded statistical confirmation. Further large multicenter studies incorporating molecular studies are needed to validate these observations.