Evaluation of MYCN immunohistochemistry as a cost-effective surrogate for MYCN genetic testing

Abstract

Background: Background: MYCN amplified neuroblastomas are associated with poor prognosis. Fluorescence in-situ Hybridization (FISH) is the recommended technique to identify MYCN amplification. However, FISH is not readily accessible in low/middle-income countries as it is an expensive technique requiring expertise in interpretation, and most pathology laboratories do not have access to fluorescence microscopes. Aim: To evaluate MYCN immunoexpression in neuroblastomas; to correlate the results with MYCN amplification status by FISH to assess if MYCN immunohistochemistry (IHC) can serve as a surrogate marker for MYCN FISH. Methods: Cases of neuroblastoma with known MYCN amplification status by FISH (MYCN/CCP2 probe set, Cytotest, USA) were retrieved. MYCN IHC (clone D4B2Y; Cell Signaling Technologies; dil 1:100) was performed in cases with adequate tissue in paraffin blocks. Staining of moderate (2+) to strong (3+) intensity in >50% of tumor cells was considered as positive. Results: Forty cases of neuroblastoma were identified. IHC could be performed in 38 cases (Table 1). Agreement between MYCN amplification and MYCN immuno-expression was seen in 29 cases (76.3%). Odds of IHC being positive in a FISH-positive specimen are 6.9 times the odds of IHC being positive in a FISH-negative specimen. Compared to FISH, IHC had a sensitivity of 54.6%, specificity of 85.2%, positive predictive value (PPV) of 60% and negative predictive value (NPV) of 82.1%. Conclusions: MYCN immunopositivity was identified in neuroblastomas with gain and non-amplified MYCN, apart from MYCN amplified cases. Although a positive association is found between MYCN FISH and IHC, as the sensitivity of IHC is low, it is not an appropriate screening test to identify cases that should undergo FISH. As the PPV is low, IHC false positive cases may lead to patients unnecessarily receiving a higher dose of chemotherapy. Thus, MYCN IHC is not an appropriate surrogate marker for determining MYCN amplification status in neuroblastomas. Further studies are required to elucidate the molecular mechanisms responsible for MYCN overexpression in non-amplified cases.