RESULTS

Patient characteristics

The patient characteristics are summarised in Table 1. A total of 273 cases of NSCLC were tested and 7 (2.6%) were found to have BRAF mutations.


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Of patients with BRAF mutations, there were three males and four females, median age 70 years, range from 51 to 76 years. All seven patients were former smokers with smoking history ranged from 3 to 90 pack years. BRAF wild-type was found in 266 cases with 141 males and 125 females, median age 66.5 years.

There was no significant difference in gender distribution (P=0.71) or age (P=0.65) between BRAF wild-type and mutant patients. Due to incomplete data on smoking history and tumour type in the BRAF wild-type group, statistical analysis could not be performed.

Table 1. Patient clinical characteristics and BRAF genotype

Patient no.
Age (years)
Gender
Smoking status
Procedure
Predominant histological subtype
other components
BRAF mutation
1 51 F Ex-smoker 15 pk yrs Lung FNA non-small cell carcinoma, NOS V600E
2 57 F Ex-smoker pk yrs not known Resection Adenocarcinoma–lepidic Papillary G469V
3 70 F Ex-smoker 10 pk yrs Resection Adenocarcinoma–micropapillary Lepidic V600E
4 70 M Ex-smoker 90 pk yrs Lung core biopsy Adenocarcinoma–acinar Papillary and lepidic K601N
5 73 F Ex-smoker 40 pk yrs Bronchial washing Adenocarcinoma V600E
6 74 M Ex-smoker 40 pk yrs Bronchial biopsy Adenocarcinoma L597Q
7 76 M Ex-smoker 3 pk yrs Resection Adenocarcinoma–micropapillary Acinar V600E
Note: F, female; M, male; NOS, not otherwise specified.

Six cases were adenocarcinomas and one case was a non-small cell carcinoma, not otherwise specified (NOS). The tumour diagnosed as non-small cell carcinoma, NOS, was from a fine needle aspiration specimen. Two cases of adenocarcinoma were diagnosed on bronchial biopsy or washing.

One case was diagnosed on core biopsy showing a mixture of acinar, papillary and lepidic patterns. In patients who underwent a resection, the histological subtypes were lepidic predominant with papillary component, micropapillary predominant with lepidic component and micropapillary predominant with acinar component. Representative H&E sections are shown in Figure 1.

BRAF mutation genotypes

Four BRAF mutation genotypes were identified. Three mutations were located in exon 15 which included V600E (c.1799T>A, 58%, n=4), K601N (c.1803A>T, 14%, n=1) and L597Q (c.1790T>A, 14%, n=1). One mutation was found in exon 11 which was G469V (c.1406G>T, 14%, n=1).

Representative spectra are shown in Figure 2. A female predominance of V600E mutations was noted (3 out of 4 V600E mutations). Furthermore, both patients with a micropapillary component harboured V600E mutation. No patient with a BRAF mutation had a concomitant EGFR or KRAS mutation.

Immunohistochemistry

Due to limited availability of tissue, BRAF V600E immunohistochemistry was only performed in three cases.BRAF V600E immunohistochemistry was positive in two cases with V600E mutation and negative in one case with K601N mutation (Figure 3).

Thus the immunohistochemistry results were consistent with the Sequenom MassArray platform results.

DISCUSSION

In our population of Australian patients with NSCLC that underwent mutation testing, we found BRAF mutations occurred in 2.6% of patients who were all former smokers.

This is consistent with other studies reporting BRAFmutation prevalence between 2-5% in NSCL14-16.

While this is much less common than EGFR mutations that occur in approximately 15% of lung adenocarcinomas in Western populations17, there were approximately 6,000 new cases of NSCLC diagnosed in Australia in 200718, giving a predicted number of 156 patients with BRAF mutant lung cancer.

These patients could potentially benefit from targeted therapy as BRAFV600E NSCLC has shown some response to dabrafenib19. The prevalence rate is only slightly lower than that of ALK gene rearrangements that are found in ~3-5% of lung adenocarcinomas20.

We found all patients with BRAF mutation had a smoking history, in contrast with EGFR mutations which commonly occur in non-smokers21.

Although others have also reported an association between BRAFmutation and smoking16, one study reported V600E mutation to be associated with non-smokers while non-V600E mutations were associated smokers14.

Discrepancies between studies may be due to low numbers ofBRAF mutant cases in each study, relating to the low prevalence of BRAF mutations in NSCLC.

A potential limitation of the targeted approach to mutation detection employed in the current study is that very rare mutations not on the OncoCarta panel may not be detected, such as BRAF mutations involving amino acids 421, 436, 439 and 471. 

However, these mutations represent less than 2% of all reported BRAF mutations in NSCLC22, making it highly unlikely for the overall BRAF mutation prevalence to be under-represented in the current study.

Furthermore our testing is more comprehensive than that performed by many centres who currently focus only of the BRAF V600 codon.