An exploration in pitfalls in interpreting SDHB immunohistochemistry

Abstract

Aims: Mutations and epimutations in genes encoding the succinate dehydrogenase complex (SDHx) are associated with multiple tumour types in which identification of SDH-deficiency has significant management implications. Immunohistochemistry (IHC) for the succinate dehydrogenase B (SDHB) subunit can help to detect SDH-deficiency, which manifests as complete loss of staining in tumour cells. However, a subset of SDH-deficient tumours can show aberrant cytoplasmic SDHB-IHC staining patterns and be misinterpreted as 'retained', a diagnostic pitfall complicating interpretation. Herein, we characterise in detail aberrant SDHB-IHC staining patterns in SDHdeficient tumours. Methods and results: We identified 23 tumours from patients with known germline SDHx and/or molecularly confirmed SDHx pathogenic/likely-pathogenic variants in their tumour. Of these, eight (35%) showed significant SDHB-IHC staining: one SDHA-, one SDHB-, three SDHC-and three SDHD-mutated cases. In all eight cases, closer inspection revealed differences in intensity and intracellular distribution of SDHB-IHC staining in tumour cells compared to adjacent non-neoplastic cells: non-neoplastic cells showed intense cytoplasmic coarse granular staining; tumour cells in seven of eight cases showed weak to focally strong, cytoplasmic blush to fine granular staining, in > 80% of cells. The remaining case in the initial block showed variably strong non-granular cytoplasmic staining with globular perinuclear accentuation throughout, only subtly distinct from the staining pattern of non-neoplastic cells. SDHB-IHC performed on two additional blocks in this latter case revealed significant intratumoral heterogeneity, including convincing areas of complete loss. Conclusions: When evaluating SDHB-IHC, care should be taken to distinguish true retained expression from aberrant cytoplasmic expression, which may be difficult to appreciate. Sometimes this may require additional molecular testing.

Composite pheochromocytoma/paraganglioma‐ganglioneuroma with a germline SDHC mutation: a first of its kind case report

“…While it is known that the SDHB stain can detect alterations in other SDHx subunits, SDHC is approximately five times less commonly implicated in germline cases and the staining patterns have not yet been well characterized 1 . In this case, the SDHB staining pattern is not completely negative (classically described) but patchy negative, which has been recently more clearly characterised as a frequent finding in the interpretation of altered SDH IHC 4 . This recently described variable loss of staining pattern is considered abnormal, with further genetic testing warranted.…”

Advancing Precision Oncology in Hereditary Paraganglioma-Pheochromocytoma Syndromes: Integrated Interpretation and Data Sharing of the Germline and Tumor Genomes

“…The interpretation of IHC results can be influenced by several factors, including protein lifespan, variant effect on protein structure, weak or diffuse SDHB staining, methodology, and normalization of IHC scores [ 25 ]. The intracellular distribution of SDHB IHC staining may vary in tumor cells, leading to complexities or variations in the interpretation of IHC results [ 26 ]. IHC at large is an effective tool; however, a lack of concordance between IHC and SDHD germline alterations has been reported [ 27 ].…”