Improving Detection of Metastatic Neuroblastoma in Bone Marrow Core Biopsies: A Proposed Immunohistochemical Approach.

Bone marrow (BM) nvolvement is common in stage 4/M neuroblastoma patients and profoundly impacts clinical decision-making and predicts outcomes, but to our knowledge no standard exists for immunohistochemical evaluation of staging BMs. We examined the use of three immuno-stains-synaptophysin, tyrosine hydroxylase (TH), and PGP9.5-in detecting metastatic neuroblastoma in BM. We retrospectively selected 174 BM core biopsies from 41 neuroblastoma patients. Immunohistochemistry for synaptophysin, TH, and PGP9.5 was performed. These slides and the hematoxylin and eosin (H&E)-stained slide from each BM were randomized and independently scored by three pathologists as positive, negative, or indeterminate. Cohen's κ coefficients (interobserver agreement), McNemar's test (for frequencies of positive/indeterminate interpretations), and sensitivities for each stain/combination were calculated. Interobserver agreement was higher for all immunostains (synaptophysin, 78%-90%, κ  =  0.548-0.787; TH, 77%-92%, κ  =  0.481-0.788; and PGP9.5, 83%-90%, κ  =  0.601-0.740) than for H&Es (77%-84%, κ  =  0.434-0.572). Indeterminate interpretations were more frequent with H&Es (8.9%) and synaptophysin (6.0%) than with PGP9.5 (3.5%) or TH (3.3%). TH (76%) and PGP9.5 (70%) were the immunostains most likely to correctly resolve indeterminate H&E interpretation. Mean sensitivity among all three pathologists for detection of metastasis compared to the consensus diagnosis was 42.5% for H&E alone, 70.7% to 78.8% for H&E plus one immunostain, and 81.6% to 85% for H&E plus two immunostains. Immunohistochemistry enhanced sensitivity for tumor detection particularly dramatically in cases of prior chemotherapy. PGP9.5 and TH showed good interobserver agreement, fewer indeterminate interpretations, and resolved indeterminate H&E diagnoses at the highest frequencies. Therefore, we recommend H&E and two immunostains, specifically PGP9.5 and TH, for optimal detection of metastatic neuroblastoma in BM.