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. 2021 Oct 11;13(20):5073.
doi: 10.3390/cancers13205073.

BRAFV600E Mutant Allele Frequency (MAF) Influences Melanoma Clinicopathologic Characteristics

Xavier Soria  1 , Felip Vilardell  2 , Óscar Maiques  3 , Carla Barceló  4 , Pol Sisó  4 , Inés de la Rosa  4 , Ana Velasco  2   5 , Dolors Cuevas  2   5 , Maria Santacana  2   5 , Sònia Gatius  2   5 , Xavier Matías-Guiu  2   5 , Alberto Rodrigo  6 , Anna Macià  7 , Rosa M Martí  1   5
Affiliations

BRAFV600E Mutant Allele Frequency (MAF) Influences Melanoma Clinicopathologic Characteristics

Xavier Soria et al. Cancers (Basel). .

Abstract

Background: Cutaneous melanoma shows high variability regarding clinicopathological presentation, evolution and prognosis.

Methods: Next generation sequencing was performed to analyze hotspot mutations in different areas of primary melanomas (MMp) and their paired metastases. Clinicopathological features were evaluated depending on the degree of variation of the BRAFV600E mutant allele frequency (MAF) in MMp.

Results: In our cohort of 14 superficial spreading, 10 nodular melanomas and 52 metastases, 17/24 (71%) melanomas had a BRAFV600E mutation and 5/24 (21%) had a NRASQ61 mutation. We observed a high variation of BRAFV600E MAF (H-BRAFV600E) in 7/17 (41%) MMp. The H-BRAFV600E MMp were all located on the trunk, had lower Breslow and mitotic indexes and predominantly, a first nodal metastasis. Regions with spindled tumor cells (Spin) and high lymphocytic infiltrate (HInf) were more frequent in the H-BRAFV600E patients (4/7; 57%), whereas regions with epithelial tumor cells (Epit) and low lymphocytic infiltrate (LInf) were predominant (6/10; 60%) and exclusive in the low BRAFV600E MAF variation tumors (L-BRAFV600E). The H-BRAFV600E/Spin/HInf MMp patients had better prognostic features and nodal first metastasis.

Conclusions: The H-BRAFV600E MMp were located on the trunk, had better prognostic characteristics, such as lower Breslow and mitotic indexes as well as high lymphocytic infiltrate.

Keywords: BRAFV600E; intratumor heterogeneity; melanoma; mutant allele frequency; next generation sequencing.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
(a) Study workflow design. (b) Heatmap showing mutated genes, demographic, clinical and tumor characteristics of our patient cohort.
Figure 2
Figure 2
MAF of BRAFV600E (a) NGS analysis of BRAFV600E MAF corrected by % of tumor cells. Patients grouped in H-BRAFV600E and L-BRAFV600E. (b) Immunohistochemical examples of primary melanoma tumor with high immunohistochemical histoscore variation of BRAFV600E between its spots and primary melanoma tumor with low immunohistochemical histoscore variation of BRAFV600E between its spots.
Figure 3
Figure 3
Clinicopathological characteristics of MMp depending on BRAFV600E MAF variation (high vs. low). (A) Heatmap showing demographic, clinical and tumor characteristics of MMp patients depending on BRAFV600E MAF variation. (B) Breslow thickness depending on BRAFV600E MAF variation and number of patients according to Breslow thickness (<4 mm vs. ≥4 mm) in primary melanoma tumors. (C) Number of mitoses and number of patients according to mitotic index (<6 vs. ≥6) depending on BRAFV600E MAF variation. (D) MMp and (E) first MMx location depending on H-BRAFV600E vs. L-BRAFV600E patients. Statistical analysis was performed using t-test, Fischer exact tests (* p < 0.05; ** p < 0.01).
Figure 4
Figure 4
(a) Patient distribution according to variation of BRAFV600E MAF (high vs. low) and lymphocytic infiltrate degree of their primary melanoma spots. (b) Patient distribution according to variation of BRAFV600E MAF and the combination of their histophenotypic characteristics and lymphocytic infiltrate degree of the primary melanoma spots. (c) Breslow thickness depending on variation of BRAFV600E MAF, cytological characteristics and lymphocytic infiltration degree and number of patients according to Breslow thickness (<4 mm vs. ≥4 mm) in primary melanoma tumors. (d) Number of mitoses and number of patients according to mitotic index (<6 vs. ≥6) depending on variation of BRAFV600E MAF, cytological characteristics and lymphocytic infiltration degree. (e) MMp and (f) first MMx location depending on H-BRAFV600E/Spin/HInf vs. L-BRAFV600E/Epit/LInf patients. Statistical analysis was performed using t-test and Fischer exact tests (* p < 0.05; ** p < 0.01).
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