A rare BRAF V600E mutation detected by next‐generation sequencing in a superficial spreading melanoma: case report and potential diagnostic implications

Dear Editor,

Increased biological and therapeutic understanding in melanoma is drastically changing the mortality rate in advanced stages. According to the COSMIC database (Catalogue Of Somatic Mutations In Cancer, April 20191), 41% of the melanomas harbour BRAF oncogene mutations and approximately 97% of BRAF mutations are situated in codon 600. The most common mutation (80–90%) is represented by a substitution of valine to glutamic acid (V600E), followed by valine to lysine (V600K; 5–12%).1 These mutations enhance BRAF activity, leading to increased phosphorylation of MAPK/ERK pathway downstream molecules, especially MEK, resulting in cell uncontrolled proliferation.2 We describe here a case of a 68‐year‐old female presenting with melanoma harbouring a rare BRAF V600E 1799_1800 TG>AA mutation.

Dermoscopic findings included irregular pigmented network, regression, irregular dots and ulceration. Histopathological examination of the lesion reported a superficial spreading melanoma of 1.6 mm Breslow thickness, Clark level III, 1 mitosis/mm² (Fig. 1a). Tumour cells expressed S‐100, MART1 and HMB45 (Fig. 1c–e).

Figure 1.

(a) Low‐power photomicrograph showing asymmetric, lentiginous and continuous melanocytic proliferation, organized in cords and solid the dermo‐epidermal junction and papillary and reticular dermis (magnification 4×); (b) high‐power photomicrograph showing atypical melanocytes with a fused appearance, altered ratio nucleus/cytoplasm, evident eosinophilic nucleolus and large, weakly eosinophilic cytoplasm, often with granules of melanotic pigment (H&E magnification 40×); the cells showed immunoreactivity for S‐100 (c), Melan‐A (d) and HMB‐45 (e) (magnification 40×).

Staging CT scan revealed multiple pulmonary metastases in the middle lobe, anterior segment of the right lower lobe (RLL) and posterior segment of the left lower lobe (LLL) (Fig. 2a). Mutational analysis of BRAF with Real‐Time PCR Kit Easy BRAF™ (DIATECH) was performed, and no mutation was detected in the BRAF gene. A nivolumab immunotherapy was immediately started, but a 4‐month follow‐up full‐body CT scan revealed pulmonary disease progression (Fig. 2b). In consideration of the inoperable condition of the metastasis, the general status of the patient and the radiologic disease progression, we decided to repeat the BRAF mutation analysis using NGS testing with Actionable Tumor Panel UMI Kit (Qiagen, Milano, Italy) and a BRAF V600E 1799_1800 TG>AA mutation was detected. Consequently, the patient could start dabrafenib and trametinib combination treatment resulting in complete disease remission after 2 months of therapy (Fig. 2c). Currently, the patient has no signs of disease.

Figure 2.

(a) Staging CT scan showing the presence of three nodular formations related to metastasis in the RLL, LLL and MLL of about 5–10 mm in diameter. (b) CT scan 4 months after metastasis appearance shows disease progression due to volumetric doubling of the three known repetitive lesions placed in the MLL, anterior segment of the RLL and posterior segment of the LLL. (c) CT scan 2 months after combo target therapy (Dabrafenib + Trametinib): complete remission of the nodular elements previously located at the pulmonary bases.

Metastatic melanoma is a disease of increasing incidence all over the world. Mutation in BRAF oncogene constitutes an important factor to direct proper treatment through targeted therapy.

Normally V600E mutation occurs when thymine is substituted with adenine at nucleotide 1799 (1799 T>A). Occasionally (89 on 302211 cases 0.029% reported on COSMIC1), this mutation can be associated with another substitution (adenine replaces guanine) taking place at nucleotide 1800 (‘complex’ mutation 1799_1800 TG>AA). Unfortunately, this mutation is not detected by the common BRAF Real‐Time PCR kits, whilst it can be easily spotted by next‐generation sequencing (NGS) method.

Indeed, BRAF V600E ‘false negative’ patients could be missing a life‐saving therapeutic option such as BRAF and MEK inhibitors. In support of our hypothesis, a recent study by Zhu et al.4 showed that out of 24 cases with negative BRAF V600E mutation analysed by allele‐specific PCR, 16 (66%) harboured an actionable (FDA‐approved therapy or available clinical trial) mutation detected by targeted NGS testing.

In addition, another study from Wheler et al.5 reported how NGS might identify potentially actionable DNA alterations that could account for target therapy–resistance, paving the way for a precision‐medicine approach in melanoma treatment.

In the near future, NGS will replace all established methods for molecular diagnostic, like PCR, for its high sensitivity and multiplexing options, allowing to generate a molecular profile of each analysed tumour sample.3

Further hypotheses and clinical studies could examine if tumour cells, harbouring a BRAF V600E 1799_1800 TG>AA mutation, are more or less responsive to immunotherapy agents as suggested by our case.

In the light of this, NGS would be especially valuable for clinicians in order to personalize the management of patients with metastatic melanoma.6 Our case highlights the importance of NGS assay as a mandatory tool for BRAF mutational status in melanoma.

Acknowledgements: None.