Use of monoclonal antibodies to detect specific mutations in formalin-fixed, paraffin-embedded tissue sections

NRAS Q61R immunohistochemical staining in thyroid pathology: sensitivity, specificity and utility

AIMS

The diagnosis of thyroid neoplasms relies upon the demonstration of histological parameters that can be focal and prone to subjective interpretation. We evaluated the utility of NRAS Q61R immunohistochemistry (IHC) in the diagnosis of thyroid lesions after determining its specificity and sensitivity as a surrogate marker for RAS Q61R mutation.

METHOD AND RESULTS

NRAS Q61R IHC was performed on 282 primary or metastatic thyroid lesions from 256 patients. RAS mutation status was collected from patients' charts. Sensitivity and specificity of NRAS Q61R IHC for detecting a RAS Q61R mutation was calculated. IHC-positive cases were reviewed to determine the diagnostic utility of NRAS Q61R IHC. NRAS Q61R immunopositivity was seen in non-neoplastic, benign and malignant thyroid lesions. NRAS Q61R antibody cross-reactivity led to the detection of NRAS Q61R, KRAS Q61R and HRAS Q61R proteins. Among primary thyroid carcinomas, immunopositivity was most frequent in papillary thyroid carcinomas, follicular variant (48.0%). The sensitivity and specificity of NRAS Q61R IHC in detecting RAS Q61R mutation was 90.6% and 92.3%, respectively. When positive, the NRAS Q61R stain was determined to be helpful in demonstrating infiltration, tumour size, capsular and/or vascular invasion and multifocality.

CONCLUSION

NRAS Q61R IHC is highly sensitive and specific for the detection of RAS Q61R mutations in thyroid pathology and is particularly relevant in follicular-patterned neoplasms. When evaluated alongside histological features, NRAS Q61R immunoreactivity can be instrumental in the diagnosis and classification of thyroid nodules.

An immunohistochemical approach to detect oncogenic CTNNB1 mutations in primary neoplastic tissues

The Wnt/β-catenin signaling pathway is dysregulated in different types of neoplasms including colorectal cancer (CRC). Aberrant activation of this signaling pathway is a key early event in the development of colorectal neoplasms, and is mainly caused by loss of function mutations in Adenomatous Polyposis Coli (APC), and less frequently by β-catenin stabilization mutations via missense or interstitial genomic deletions in CTNNB1. In this study, we have defined an immunohistochemical algorithm to dissect Wnt pathway alterations in formalin-fixed and paraffin-embedded neoplastic tissues. Basically, consecutive sections of tumor specimens were stained by immunohistochemistry with two different monoclonal antibodies against β-catenin: one (anti-active β-catenin antibody) recognizes hypo-phosphorylated β-catenin and the other recognizes the total pool of β-catenin. We validated the strategy in the HCT116 CRC cell line which has an in-frame deletion of β-catenin serine 45, and then studied human tumor microarrays containing colon adenomas, CRCs, solid pseudopapillary neoplasms of the pancreas as well as the whole tissue sections of CRCs, desmoid fibromatosis, and pilomatrixoma of the skin. In some tumors, we found strong β-catenin cytoplasmic and/or nuclear staining with the total β-catenin antibody but no staining with the anti-active β-catenin antibody. This was inferred to be an altered/mutant β-catenin staining pattern. All six colon adenomas of the 126 total adenomas studied for the altered/mutant β-catenin staining pattern had presumptively pathogenic point mutations or deletions in CTNNB1. Four of 10 CRCs with the alterated/mutant β-catenin staining pattern studied in depth, from 181 total CRCs from tissue microarray, had pathogenic CTNNB1 mutations. The frequencies of CTNNB1 alterations in non-colonic tumors with altered/mutant β-catenin staining ranged between 46 and 100%. Our results demonstrate that the immunohistochemical approach described here can detect oncogenic forms of β-catenin in primary tissue samples and can also highlight other tumors with presumptive novel defects activating the Wnt/β-catenin pathway.

Immunohistochemistry-Enabled Precision Medicine

Immunohistochemistry (IHC) can be applied to diagnostic aspects of pathologic examination to provide aid in assignment of lineage and histologic type of cancer. Increasingly, however, IHC is widely used to provide prognostic and predictive (theranostic) information about the neoplastic disease. A refinement of theranostic application of IHC can be seen in the use of "genomic probing" where antibody staining results are directly correlated with an underlying genetic alteration in the tumor (somatic mutations) and/or the patient (germline constitution). All these aspects of IHC find their best use in guiding the oncologists in the optimal use of therapy for the patients.

Peptide Antibodies in Clinical Laboratory Diagnostics

Peptide antibodies, with their high specificities and affinities, are invaluable reagents for peptide and protein recognition in biological specimens. Depending on the application and the assay, in which the peptide antibody is to used, several factors influence successful antibody production, including peptide selection and antibody screening. Peptide antibodies have been used in clinical laboratory diagnostics with great success for decades, primarily because they can be produced to multiple targets, recognizing native wildtype proteins, denatured proteins, and newly generated epitopes. Especially mutation-specific peptide antibodies have become important as diagnostic tools in the detection of various cancers. In addition to their use as diagnostic tools in malignant and premalignant conditions, peptide antibodies are applied in all other areas of clinical laboratory diagnostics, including endocrinology, hematology, neurodegenerative diseases, cardiovascular diseases, infectious diseases, and amyloidoses.