EGFR and K-Ras mutations in women with lung adenocarcinoma: implications for treatment strategy definition

The epidermal growth factor receptor (EGFR) and K-Ras are among the most investigated molecular drivers in solid tumors. In particular, EGFR is addressed as an interesting target for several biologic agents, mainly monoclonal antibodies (acting at the cellular surface level) and small molecules (inhibiting the intracellular tyrosine-kinase domain activity) [1]. EGFR overexpression often correlates with a worse prognosis is several tumors [2] and the blockade of the EGFR-driven cascade has been proved successful in non-small cell lung cancer (NSCLC), colorectal, head and neck and breast cancer [1]. Mutations in K-Ras, occurring at different levels along the gene sequence, have been described in multiple malignancies [3]. Moreover, K-Ras has been the first predictive biomarker identified and routinely used in advanced colorectal cancer management: mutations in this key oncogene predict the benefit from the anti-EGFR monoclonal antibodies panitumumab and cetuximab [4], and the role of mutations in different Ras family members (such as N-Ras) is rapidly emerging as an essential tool for patient selection in this disease [5].

NSCLC in women is a growing health concern in Western countries [6]. Gender-related factors (modulating smoking-dependent and independent carcinogenesis) may contribute to this increased incidence [7]. The disease is reported as a peculiar pathological and molecular entity: in particular, women are more often affected by lung adenocarcinoma and the tumor arises among never- or light-smokers with higher frequency than in men [7].

Following the observation that female gender was one of the clinical features associated with a benefit from anti-EGFR tyrosine-kinase inhibitors (TKIs) (together with Asian origin, adenocarcinoma histology and smoking habits) [8],[9], deeper insights into the EGFR biology allowed to identify somatic mutations in the kinase domain of the EGFR gene [10]. Nowadays, EGFR mutational status is a well-recognized predictive factor for anti-EGFR TKIs activity and an essential tool for treatment allocation in advanced lung adenocarcinoma [11].

However, the impact of first-line platinum-based chemotherapy (CT) in female patients with EGFR mutated adenocarcinoma is a matter of debate and no definitive data emerge from subgroup analyses of randomized trials comparing CT with TKIs in the first-line setting [8]. The results of a recent meta-analysis of prospective and retrospective studies suggest that EGFR mutations may be associated with higher response rate (RR) to CT, but may not predict the benefit of CT with regard to progression-free survival (PFS) and overall survival (OS) [12].

Among the other molecular aberrations involved in NSCLC progression, K-Ras is certainly one of the most extensively studied [13]: K-Ras mutations (mainly located in codons 12 and 13 of exon 2) are reported in up to 30% of NSCLC cases [13],[14], especially among smokers. It is worth noting that EGFR and K-Ras mutations are rarely found in the same tumor, suggesting that they may drive functionally different carcinogenetic processes [13],[14]. Direct targeting of K-Ras has recently raised some concerns, as this represents a key transduction pathway in both normal and tumor tissues. Moreover, several parallel escape mechanisms have been identified [15]. Moving from these considerations, alternative targeting of K-Ras is currently under evaluation, e.g. by inhibiting BRAF or MEK activity [15].

Inconclusive evidence exists about the role of K-Ras mutations in predicting the benefit of CT in lung adenocarcinoma [16]. On the other hand, retrospective subgroup analyses seem to suggest that patients with K-Ras mutated tumors show a primary resistance to anti-EGFR TKIs [14]. Two meta-analyses demonstrated that the objective RR to anti-EGFR TKIs in K-Ras mutated tumors is inferior to wild-type ones [17],[18]. However, no definitive conclusion was reported in terms of PFS and OS.

In our clinically enriched series (Caucasian women with lung adenocarcinoma) we aimed at investigating the possible predictive significance of EGFR and K-Ras mutations with respect to both first-line platinum-based CT and salvage treatment with the anti-EGFR TKI erlotinib.

We retrospectively evaluated the outcomes of Caucasian women with lung adenocarcinoma, undergoing first-line platinum-based CT and subsequent salvage anti-EGFR TKI therapy, in relation to EGFR and K-Ras mutational status.

The clinical selection we applied (i.e. by gender and histology), together with the high percentage of never smokers in our series, is probably responsible for the high incidence of EGFR mutations (30%) and the low frequency of K-Ras mutations (13%) observed. As expected, K-Ras mutations were more frequent in current smokers, while a formally significant influence of smoking habits on the EGFR mutation rate was not detected: this was probably due to the small sample size and the potential confounding effect of other clinical selection criteria, such as gender and histology. In our series no patient had concomitant EGFR and K-Ras mutations.

Patients received first-line platinum-based CT according to clinical characteristics and physicians' choice. Retrospectively, the correlation between clinical parameters (RR, PFS and OS) and EGFR and K-Ras mutational status showed that women with EGFR mutant tumor achieved a marginally lower RR to first-line platinum-based combination (32% vs. 43%; p = 0.579) and a significantly shorter PFS (4.4 vs. 6.4 months; HR 0.597; p = 0.048) compared to those with wild-type disease. There was no impact of the type of EGFR mutations on the PFS results and, as observed by previous reports, K-Ras mutations did not play a role in predicting the benefit from standard CT [16]. The effect of EGFR status on the efficacy of first-line platinum-based CT has been only rarely reported in the majority of studies and always with conflicting results [12]. The most recent and reliable data may be derived from trials of first-line CT vs. anti-EGFR TKIs or CT plus a third targeted agent in molecularly unselected patients [8]. However, none of the reported analyses demonstrated a significant impact of EGFR mutational status on the benefit from first-line platinum-containing CT. Looking at the published or presented results, most trials suggest no role or, at best, slightly better outcome for patients with EGFR mutant tumor when treated with first-line CT [8],[12]. However, this remains an open issue and a definitive answer cannot be given since it would, in any case, suffer from several limitations (e.g., no gender selection, retrospective and unplanned nature of the analyses). Our series included only women with lung adenocarcinoma: female gender is an established good prognostic factor in NSCLC independently of disease stage, molecular status and treatment [20] and we cannot exclude a potential synergistic effect of gender and EGFR mutational status on the results we reported. Clinical enrichment in our study could also be the cause of the interesting median OS we observed (up to 29.5 months), not always reached in a population of unselected advanced NSCLC patients. However, although limited in size, our results further confirm the need of an upfront molecular characterization of all patients with lung adenocarcinoma before starting first-line treatment. In our series 5 patients with EGFR mutant disease died without receiving any anti-EGFR treatment, mainly because of a rapid worsening of performance status due to disease progression after first-line CT. Considering the huge amount of data supporting the superiority of anti-EGFR TKIs compared with CT in these patients, every effort should be made to clarify the molecular profile of a lung adenocarcinoma before starting any treatment in everyday clinical practice.

Thirty-nine women received salvage erlotinib irrespectively of EGFR or K-Ras mutational status. EGFR mutations are a recognized predictive biomarker [11] and a regulatory requirement for the use of an anti-EGFR TKI as first-line approach [21]. Therefore, it is not surprising that, in our series, the benefit from erlotinib administered at progression was restricted to EGFR mutant cases both in terms of RR (p = 0.004) and PFS (HR 0.491; p = 0.044). Moreover, women with EGFR mutant tumor treated with front-line CT and salvage anti-EGFR TKI showed a trend toward a better OS in comparison with those affected by EGFR wild-type tumor undergoing the same sequence (HR 0.560; p = 0.131). We might speculate that the disadvantage in PFS obtained with first-line CT in EGFR mutated women can be counterbalanced by the better results achieved with salvage anti-EGFR TKI. However, since a significant proportion of women with EGFR mutant tumors received no anti-EGFR TKI after first-line CT, once again we believe that these results stress the importance of a pre-specified sequence of approaches (upfront TKI followed by salvage CT) in women harboring molecularly-addicted tumors in order to achieve the best outcome. The lack of any impact of the type of EGFR mutation on PFS could be due, at least in part, to the limited number of cases in our series.

In our clinically enriched population K-Ras mutations were not predictive of benefit from CT. As a matter of fact no difference in RR (33% vs. 39%) and PFS (5.0 vs. 5.3 months) was observed between patients with K-Ras mutant tumor and those with wild-type disease. The most recent report in a similar setting (i.e. EGFR wild-type patients treated with erlotinib after progression to first-line CT) was the retrospective evaluation of K-Ras status in the TAILOR study [22]. In this randomized phase III trial K-Ras mutations were neither prognostic nor predictive of benefit from docetaxel and no significant interaction was demonstrated between K-Ras status and PFS or OS.

On the contrary, our results seem to suggest a putative negative predictive significance of K-Ras mutations for anti-EGFR TKI activity. None of the patients with K-Ras mutant tumor achieved an objective response with salvage erlotinib and these patients experienced a significantly worse median PFS (HR 0.284; p = 0.010) and OS (HR 0.158; p < 0.001) compared with patients affected by wild-type NSCLC. Considering that the benefit from CT did not differ between the two groups and that K-Ras mutated women experienced not only a significantly shorter PFS on TKI but, in particular, a significantly reduced OS, we could argue that TKI administration in such a population could be potentially detrimental. However the limited number of patients in our series prevents us from drawing any definitive conclusion. Other larger data sets did not suggest any relevance of K-Ras mutations in determining the benefit of CT [16], and taking into account the above mentioned conflicting results about the predictive role for anti-EGFR TKIs [17],[18], we do not believe that routine K-Ras sequencing should be considered in all patients with lung adenocarcinoma outside clinical and translational trials. This is particularly relevant when the tumor is not easily accessible for biologic sample collection and thus oncologists need to spare tissue for fundamental analyses, such as EGFR mutations and EML4-ALK translocation.

In our series of Caucasian women with advanced adenocarcinoma of the lung EGFR mutations seem to be associated with lower benefit from first-line platinum-based CT. If confirmed in larger, prospectively collected, datasets these results may help to shed light on the potential influence of gender on EGFR biology in NSCLC. We confirmed that the presence of an EGFR mutation strongly predicts the benefit of salvage treatment with erlotinib, stressing the role of this drug as first-line option in molecularly selected patients. The role of K-Ras mutations as biomarkers of resistance to anti-EGFR TKIs in NSCLC is still unclear and surely deserves further investigations.