Daniela Massi et al., Immunohistochemistry is highly sensitive and specific for the detection of NRASQ61R mutation in melanoma. Modern Pathology

Daniela Massi1, Lisa Simi2, Elisa Sensi3, Gianna Baroni1, Gongda Xue4, Cristian Scatena1, Adele Caldarella5, Pamela Pinzani2, Gabriella Fontanini3, Alessandra Carobbio6, Carmelo Urso7 and Mario Mandalà8

1Division of Pathological Anatomy, Department of Surgery and Translational Medicine, University of Florence, Florence, Italy
2Clinical Biochemistry Unit, Department of Biomedical, Experimental and Clinical Sciences, University of Florence, Florence, Italy
3Laboratory of Molecular Pathology, UO Pathological Anatomy III, Pisa, Italy
4Unit of Mechanisms of Cancer, Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
5Clinical and Descriptive Epidemiology Unit, Institute for Study and Cancer Prevention (ISPO), Florence, Italy
6Research Foundation, Papa Giovanni XXIII Hospital, Bergamo, Italy
7Dermatopathology Section, SM Annunziata Hospital, Florence, Italy
8Unit of Medical Oncology, Division of Medical Oncology, Department of Oncology and Haematology, Papa Giovanni XXIII Hospital, Bergamo, Italy


Testing for NRAS is now integral part in the assessment of metastatic melanoma patients because there is evidence that NRAS-mutated patients may be sensitive to MEK inhibitors, and RAS mutation is a common mechanism of acquired resistance during treatment with BRAF inhibitors. This study evaluated the sensitivity and specificity of immunohistochemical analysis using an N-Ras (Q61R) antibody to detect the presence of the NRASQ61R mutation in melanoma patients. A total of 98 primary cutaneous melanomas that have undergone examination of NRAS mutation were retrieved from a multicentric database. Formalin-fixed and paraffin-embedded melanoma tissues were analyzed for BRAF and NRAS mutations by independent, blinded observers using both conventional DNA molecular techniques and immunohistochemistry with the novel anti-human N-Ras (Q61R) monoclonal antibody (clone SP174). The antibody showed a sensitivity of 100% (14/14) and a specificity of 100% (83/83) for detecting the presence of an NRASQ61R mutation. Of the NRAS-mutated cases, none of the non-Q61R cases stained positive with the antibody (0/7). There were three cases with discordant NRAS mutational results. Additional molecular analysis confirmed the immunohistochemically obtained NRAS result in all cases, suggesting that a multiple analytical approach can be required to reach the correct sample classification. The reported immunohistochemical method is an accurate, rapid, and cost-effective method for detecting NRASQ61R mutation in melanoma patients, and represents a valuable supplement to traditional mutation testing. If validated in further studies, genetic testing would only be required for immunohistochemistry-negative patients to detect non-Q61R mutations.

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