Arnaud Uguen1–3, Matthieu Talagas2–4, Marc De Braekeleer1,3,5 and Pascale Marcorelles2–4
1Inserm, U1078, Department of Pathology, CHRU Brest, University Hospital Morvan, 5, Avenue Foch, FR-29609 Brest, 3Université Européenne de Bretagne, 4Faculté de Médecine et des Sciences de la Santé Université de Brest, and 5CHRU Brest, Laboratoire de Cytogénétique et Biologie de la Reproduction, Brest, France. E-mail: arnaud.uguen@chu-brest.fr
Accepted Nov 12, 2015; Epub ahead of print Nov 16, 2015
Sir,
We read with interest the article by Ashida et al. (1), describing a patient with metastatic melanoma who presented with a BRAFV600E mutation diagnosed only in circulating cell-free DNA with no detected mutation in the primary formalin-fixed and paraffin-embedded (FFPE) tumour. Molecular analysis of FFPE melanoma samples, primary or metastatic, is the main method of diagnosing a BRAFV600 mutation, enabling anti-BRAF targeted therapy. Nevertheless, detection of BRAF mutations in circulating cell-free DNA offers a good opportunity to progress the monitoring and diagnosis of patients with metastatic melanoma, especially in cases with challenging metastatic sites with surgical issues that impair tumour sampling (2, 3). However, this new method requires heavily-specialized molecular genetics platforms. As an alternative, mutation-specific immunohistochemistry, a widespread and rapid technique available in most pathology laboratories, allows the detection of BRAFV600E mutated protein with excellent sensitivity and specificity, especially in challenging melanoma samples containing few tumour cells (4–7) (see Fig. 1 for an example from our laboratory). We hypothesize that anti-BRAFV600E immunohistochemistry, performed on the primary melanoma, could have enabled a conclusion to be reached at the time of diagnosis in the case of a BRAFV600E mutated melanoma reported by Ashida et al. (1), without requiring cell-free tumour DNA analysis.
Fig. 1. Cell-poor melanoma sample stained with anti-BRAFV600E immunohistochemistry. The lateral component of this BRAFV600E-mutated superficial spreading malignant melanoma showed immunostaining of junctional and trans-epidermis pagetoid ascending (arrows) melanoma cells. The high number of non-tumour cells prevented detection of the BRAFV600E mutation through molecular pyrosequencing analysis (haematoxylin counter-staining, original magnification ×25).
Atsuko Ashida, Hisashi Uhara, Asuka Mikoshiba, Kaori Sakaizawa, Naomi Kumagai, Hiroshi Koga, Ryuhei Okuyama*
Department of Dermatology, Shinshu University School of Medicine, 3-1-1 Asahi, Matsumoto 390-8621, Japan. *E-mail: rokuyama@shinshu-u.ac.jp
We thank Uguen et al. for their comments and would like to take this opportunity to reply.
Detection of BRAF mutations is important for melanoma treatment. As noted by Uguen et al., mutation-specific immunohistochemistry is beneficial in detecting tumour cells with BRAFV600E mutation. We did not intend to exclude the possibility that immunohistochemistry would allow the detection of a specific mutation in the primary lesion in our case. On the other hand, analytical methods for circulating cell-free DNA usually require highly specialized platforms. However, castPCR (Competitive Allele-Specific TaqMan polymerase chain reaction) does not require advanced procedures or specific instruments other than a real-time PCR system. In fact, castPCR reagent kits are available commercially. We consider castPCR to be a readily accessible technique, which could help in identifying melanoma patients who would benefit from targeted anti-BRAF therapy.
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