PHOX2B Immunostaining: A Simple and Helpful Tool for the Recognition of Ganglionic Cells and Diagnosis of Hirschsprung Disease

PHOX2B: a diagnostic cornerstone in neurocristopathies and neuroblastomas

Paired-like homeobox 2B (PHOX2B) is a gene essential in the development of the autonomic nervous system. PHOX2B mutations are associated with neurocristopathies-Hirschsprung disease (HSCR) and congenital central hypoventilation syndrome (CCHS)-and peripheral neuroblastic tumours. PHOXB2 plays an important role in the diagnostics of these conditions.Genotyping of a PHOX2B pathogenic variant is required to establish a diagnosis of CCHS. In HSCR patients, PHOX2B immunohistochemical staining has proven to be a valuable tool in identifying this disease. Furthermore, PHOXB2 is a predisposition gene for neuroblastoma, in which PHOX2B immunohistochemical staining can be used as a highly sensitive and specific diagnostic marker. The utility of PHOX2B immunohistochemistry in pheochromocytoma and paraganglioma has also been studied but yields conflicting results.In this review, an overview is given of PHOX2B, its associated diseases and the usefulness of PHOX2B immunohistochemistry as a diagnostic tool.

Hand2 Immunohistochemistry in the Diagnosis of Paragangliomas and Other Neuroendocrine Neoplasms

Hand2 is a core transcription factor responsible for chromaffin cell differentiation. However, its potential utility in surgical pathology has not been studied. Thus, we aimed to investigate its expression in paragangliomas, other neuroendocrine neoplasms (NENs), and additional non-neuroendocrine tumors. We calibrated Hand2 immunohistochemistry on adrenal medulla cells and analyzed H-scores in 46 paragangliomas (PGs), 9 metastatic PGs, 21 cauda equina neuroendocrine tumors (CENETs), 48 neuroendocrine carcinomas (NECs), 8 olfactory neuroblastomas (ONBs), 110 well-differentiated NETs (WDNETs), 10 adrenal cortical carcinomas, 29 adrenal cortical adenomas, 8 melanomas, 41 different carcinomas, and 10 gastrointestinal stromal tumors (GISTs). Both tissue microarrays (TMAs) and whole sections (WSs) were studied. In 171 NENs, previously published data on Phox2B and GATA3 were correlated with Hand2. Hand2 was positive in 98.1% (54/55) PGs, but only rarely in WDNETs (9.6%, 10/104), CENETs (9.5%, 2/21), NECs (4.2%, 2/48), or ONBs (12.5%, 1/8). Any Hand2 positivity was 98.1% sensitive and 91.7% specific for the diagnosis of PG. The Hand2 H-score was significantly higher in primary PGs compared to Hand2-positive WDNETs (median 166.3 vs. 7.5; p < 0.0001). Metastatic PGs were positive in 88.9% (8/9). No Hand2 positivity was observed in any adrenal cortical neoplasm or other non-neuroendocrine tumors, with exception of 8/10 GISTs. Parasympathetic PGs showed a higher Hand2 H-score compared to sympathetic PGs (median H-scores 280 vs. 104, p < 0.0001). Hand2 positivity in NENs serves as a reliable marker of primary and metastatic PG, since other NENs only rarely exhibit limited Hand2 positivity.

Hirschsprung disease

Hirschsprung disease (HSCR) is a rare congenital intestinal disease that occurs in 1 in 5,000 live births. HSCR is characterized by the absence of ganglion cells in the myenteric and submucosal plexuses of the intestine. Most patients present during the neonatal period with the first meconium passage delayed beyond 24 h, abdominal distension and vomiting. Syndromes associated with HSCR include trisomy 21, Mowat-Wilson syndrome, congenital central hypoventilation syndrome, Shah-Waardenburg syndrome and cartilage-hair hypoplasia. Multiple putative genes are involved in familial and isolated HSCR, of which the most common are the RET proto-oncogene and EDNRB. Diagnosis consists of visualization of a transition zone on contrast enema and confirmation via rectal biopsy. HSCR is typically managed by surgical removal of the aganglionic bowel and reconstruction of the intestinal tract by connecting the normally innervated bowel down to the anus while preserving normal sphincter function. Several procedures, namely Swenson, Soave and Duhamel procedures, can be undertaken and may include a laparoscopically assisted approach. Short-term and long-term comorbidities include persistent obstructive symptoms, enterocolitis and soiling. Continued research and innovation to better understand disease mechanisms holds promise for developing novel techniques for diagnosis and therapy, and improving outcomes in patients.

Phox2B is a sensitive and reliable marker of paraganglioma-Phox2B immunohistochemistry in diagnosis of neuroendocrine neoplasms

Phox2B is a transcription factor responsible for chromaffin cell phenotype. Although it is used routinely for diagnosis of neuroblastoma, previous reports concerning its utility in the diagnosis of neuroendocrine neoplasms have been conflicting. We assessed Phox2b immunoreactivity in different neuroendocrine neoplasms. Tissue microarrays or whole sections of 36 paragangliomas (PGs), 91 well-differentiated neuroendocrine tumours of different organs (WDNETs), 31 neuroendocrine carcinomas (NECs), and 6 olfactory neuroblastomas (ONBs) were stained with Phox2B antibody (EP312) and GATA3. The percentage of positive cells and intensity was analysed using H-score. Phox2B immunoreactivity was seen in 97.2% (35/36) PGs, 11% (10/91) WDNETs, 9.7% (3/31) NECs, and 16.7% (1/6) ONBs. PGs were significantly more often positive (p < 0.001, χ²) than other neuroendocrine tumours, showing highest H-score (mean 144.9, SD ± 75.1) and percentage of positive cells (median 81.3%, IQR 62.5-92.5%). Compared to Phox2B-positive WDNETs, PGs showed significantly higher H-score (median 145 vs 7.5, p < 0.001) and percentage of positive cells (median 82.5% vs 4.5%, p < 0.001). Phox2B positivity was 97.2% sensitive and 89% specific for the diagnosis of PG. GATA3 was 100% sensitive and 88% specific for the diagnosis of PG. When combined, any Phox2B/GATA3 coexpression was 97.1% sensitive and 99.1% specific for the diagnosis of paraganglioma. Widespread Phox2B immunoreactivity is a highly characteristic feature of PGs and it can be used as an additional marker in differential diagnosis of neuroendocrine tumours.