Validated Antibodies For Neuroendocrine Tumors (NENs)
Neuroendocrine neoplasms (NENs) constitute a group of tumors that derive from the sensory and secretory neuroendocrine cells of the diffuse endocrine system. There is an unmet need for accurate biomarkers that can be used for NEN diagnosis, prognosis and follow-up, therapy stratification, and evaluation of treatment response. The high diversity of neuroendocrine neoplasms requires the development of specific biomarkers for their identification, diagnosis, and management.
This resource provides a complete overview of first and second-generation NEN markers, diagnostic algorithms, and the validated antibodies required to clarify your research.
The Crucial Need for New NEN Biomarkers
NENs management remains a challenge due to a number of aspects such as lack of profound knowledge of the biology of the disease, late clinical presentation, and the scarcity of effective treatment options. A correct diagnosis is imperative for the patient to obtain the most efficient treatment.
In fact, the ultimate NEN diagnosis can only be established with tissue biopsy and further tumor grading based on the combination of Ki-67 proliferative index with cell mitotic rate. The Ki-67 index is the standard routine for measuring NEN proliferation to define the tumor grade. It also has both prognostic and predictive value, as a Ki-67 proliferation index >2% is a significant predictor of progression-free survival.
While Ki-67 is essential for grading, a critical limitation in NEN management is the lack of accurate markers for classification, monitoring therapy, and providing a prognostic assessment.
Key Biomarkers by NEN Type (pNET, GI-NET, BP-NET)
Pancreatic Neuroendocrine Tumor (pNET):
Chromogranin A (CgA): Elevated levels of CgA are commonly observed in the blood of patients with pNETs. CgA serves as a biomarker for diagnosis and monitoring disease progression.
Synaptophysin: Immunohistochemical staining for synaptophysin is frequently used to confirm the neuroendocrine nature of tumors, including pNETs, making it a crucial marker for identification.
Gastrointestinal Neuroendocrine Tumor (GI-NET):
Somatostatin Receptor (SSTR): The expression of somatostatin receptors, particularly SSTR2A, is a key feature of GI-NETs. Imaging with somatostatin analogs labeled with radionuclides helps in localization and staging.
Neuron-Specific Enolase (NSE): NSE is often elevated in the blood of patients with GI-NETs, serving as a biomarker for both diagnosis and monitoring of treatment response.
Bronchopulmonary Neuroendocrine Tumor (BP-NET):
CD56 (Neural Cell Adhesion Molecule): CD56 is commonly expressed in BP-NETs and is used as an immunohistochemical marker for their identification.
Progastrin-Releasing Peptide (ProGRP): ProGRP levels in the blood are elevated in patients with small cell lung cancer, including BP-NETs, and are utilized as a biomarker for diagnosis and monitoring.
First-Generation NEN Markers: The Gold Standard
Most NENs produce and secrete a multitude of proteins that can be detected by IHC. The most important "first-generation" markers are Chromogranin A (CgA) and Synaptophysin (SYP), which are considered the most specific markers of NEN differentiation. In addition, expression of CD56 and Neuron-Specific Enolase (NSE) are adequate evidence of neuroendocrine differentiation.
While these markers are the standard, they offer little help in determining the NEN’s primary location. Moreover, highly proliferative NENs recurrently lose the ability to express CgA and SYP, making the diagnosis challenging.
| Scope | IHC Markers |
|---|---|
| Confirmation of neuroendocrine nature | Markers for neuroendocrine differentiation: Chromogranin A, Synaptophysin, CD56, CD57, UCHL1, NSE |
| Confirmation of epithelial origin | Markers for epithelial differentiation: Cytokeratins AE1/AE3, CAM5.2, CK18, CK8 |
| Grading and staging | Marker for tumor proliferation: Ki-67 |
Second-Generation NEN Markers: The New Standard for Clarity
The advent of second-generation NEN markers for use in IHC has considerably expanded the pathology toolbox. These markers (functionally distinct from CgA and SYP) are more consistent in terms of expression, even if the NEN downregulates its secretory machinery. As non-NENs rarely express these antigens, their specificity makes them welcome additions to clinical practice.
INSM1 (Insulinoma-associated protein 1)
The nuclear transcription factor INSM1 is a novel sensitive and specific marker that has demonstrated excellent sensitivity and specificity for NET differentiation in various anatomic sites. INSM1 is more sensitive than SYP/CHGA in NECs. In addition, its nuclear expression pattern offers an advantage in interpretation over first-generation markers, which are all cytoplasmic. INSM1 has been proposed as a more sensitive marker than conventional neuroendocrine markers for pulmonary NENs.
ISL1 (ISL LIM Homeobox 1)
ISL1 (or ISLET1) is a transcription factor involved in the differentiation of the neuroendocrine pancreatic cells. It binds the insulin gene promoter and regulates insulin gene expression. Hence, ISL1 is a reliable standard marker of pancreatic well-differentiated NENs but is also commonly found in NENs of extra-pancreatic origin.
SCGN (Secretagogin)
Secretagogin (SCGN or SECG) is a calcium-binding protein highly expressed in neuroendocrine cells. High SCGN expression is found in the cytosol and nuclei of well-differentiated NENs originating from different organs, as well as in NENs from the lung, pancreas, and adrenal glands, promoting SCGN as a novel marker of NETs differentiation. SCGN is more sensitive and specific in large cell neuroendocrine carcinoma than first-generation markers.
OTP (Orthopedia homeobox protein)
Orthopedia homeobox protein (OTP) is a nuclear transcription factor with a well-defined role in embryonic neurodevelopment. OTP was suggested as a diagnostic and prognostic marker for pulmonary NENs, being strongly expressed in NET cells (typical and atypical carcinoid) but not in NECs. High OTP expression is a highly sensitive and specific marker for favourable prognosis of pulmonary carcinoid tumors.
Visualizing NEN Markers: IHC & Multiplex Examples
Seeing these markers in context is critical for confirming expression and co-localization. Below are examples of first and second-generation markers visualized in human tissue using IHC, IF, and multiplex IF.
1. Immunofluorescence staining of HeLa cells using the monoclonal antibody Anti-ISL1 (AMAb91729), showing localization to nucleoplasm and cytosol in green. Microtubules are visualized in red.
2. Immunohistochemical staining of human pancreas sing the monoclonal antibody Anti-INSM1 (AMAb91727) shows strong nuclear positivity in islets of Langerhans, in brown.
3. Immunohistochemical staining of human lung tumor (typical carcinoid) using the monoclonal Anti-OTP (AMAb91696) antibody shows strong nuclear positivity in tumor cells, in brown.
4. Immunohistochemical staining of human duodenumu sing the monoclonal antibody Anti-SCGN (AMAb90630) shows strong immunoreactivity in the neuroendocrine cells as well as in the local ganglionic cells, in brown.
5. Multiplexed IHC-IF staining of human lung tumor (atypical carcinoid) using the monoclonal antibody Anti-OTP AMAb91695 (nuclear, red) and the polyclonal antibody Anti-CD44 (HPA005785, green). Nuclei are counterstained by DAPI (blue).
6. Multiplexed IHC-IF staining of human pancreas showing CHGB and CHGA expression in pancreatic islet, using the monoclonal antibody Anti-CHGB (AMAb91709, cytoplasmic, green) and the polyclonal antibody Anti-CHGA (HPA017369, cytoplasmic, red). Nuclei are counterstained by DAPI (in blue).
7. Multiplexed IHC-IF staining of human pancreas showing CHGB and SCGN expression in pancreatic islet, using the monoclonal antibodies Anti-CHGB AMAb91709 (cytoplasmic, in green) and Anti-SCGN AMAb90632 (cytoplasmic and nuclear, in red). Nuclei are counterstained by DAPI (in blue).
8. Multiplexed IHC-IF staining of human duodenum showing CHGB and CHGA expression in enteroendocrine cell, using the monoclonal antibody Anti-CHGB AMAb91709 (cytoplasmic, in green) and the polyclonal antibody Anti-CHGA HPA017369 (cytoplasmic, in red). Note colocalisation of markers in the enteroendocrine cell. Nuclei are counterstained by DAPI (in blue).