A Rare p.T599dup BRAF Mutant NSCLC in a Non-Smoker

V-RAF murine sarcoma viral oncogene homolog B1 (BRAF) mutated non-small-cell lung cancer (NSCLC) is an exceptionally rare form of lung cancer, found only in one to two percent of patients with an NSCLC diagnosis. BRAF NSCLC traditionally affects former or active smokers. BRAF mutations have always been of special interest to the oncological community, as they offer potential for targeted therapies. BRAF mutation spectrum includes mutations that are of both V600 and non-V600 types. BRAF V600 is an activating mutation, which results in high kinase activity and overproduction of active oncoproteins such as rapidly accelerated fibrosarcoma (RAF). This makes them susceptible to targeted therapies with RAF inhibitors. There has been little evidence, however, regarding efficacy of RAF inhibitors towards non-activating mutations that have intermediate to low kinase activity, such as non-V600 BRAF mutations. While several approaches have been investigated to overcome the limitations of RAF inhibitors, such as use of mitogen-activated protein kinase kinase (MEK) and extracellular signal-regulated kinase (ERK) inhibitors or combination of MEK and RAF inhibitors, none of them have been proven to have a superior efficacy for low kinase activity non-V600 BRAF tumors. We present a case of an extremely rare variant of NSCLC BRAF p.T599dup mutation in a non-smoker that responded to a targeted combination therapy with RAF and MEK inhibitors. The patient responded well to therapy that usually targets high kinase activity V600 mutations. Our hope is to bring more attention to non-V600 mutations and document their responses to existing and new therapies.