Molecular profiles of EGFR, K-ras, c-met, and FGFR in pulmonary pleomorphic carcinoma, a rare lung malignancy

PPC is a rare aggressive disease characterized by a high rate of distant recurrence after initial surgery for localized disease (Hong et al. 2009). There is presently no available data indicating the optimal management of patients with this advanced disease. In particular, the role of chemotherapy remains unclear, and these patients are often treated according to the results of trials of enrolled patients with NSCLC, such as squamous cell carcinoma or adenocarcinoma. Many targeted agents are widely used for the treatment of patients with advanced NSCLC. However, whether these drugs have some activity in PPC is not yet clear.

EGFR, K-ras, c-met, and FGFR are receptor tyrosine kinases (RTKs) frequently activated by gene amplification or mutation in a variety of human neoplasm especially lung cancer. EGRF and K-ras have been already well-known target genes in NSCLC. The occurrence of MET amplification and EGFR/K-ras mutation might be mutually exclusive suggesting several distinct mechanisms in the development of NSCLC (Onitsuka et al. 2010). FGFR-mediated signals in cooperation with those transmitted by EGFR are involved in growth and survival of human NSCLC cells and should be considered as targets for combined therapeutic approaches (Fischer et al. 2008). Various RTKs have come into the focus of therapeutic considerations since they can be targeted by pharmaceutical intervention and because tumors bearing oncogenic RTK mutations generally show a good response to targeted therapy.

To gain further insight into the clinical targetabilities of PPCs, we performed a molecular analysis of 61 resected PPCs. Previous studies have analyzed only a small number of tumors and have mostly focused on histological and clinical characteristics of this rare disease entity. Thus, this study is one of the first attempts to genetically characterize PPCs, with the underlying premise of rapidly extending this knowledge to clinical oncology practices. Several characteristics of PPCs emerged from these analyses. Mutational analysis of PPCs demonstrated that about half of the patients possess one or multiple combinations of the above five genetic abnormalities. The activating EGFR mutations were seen in 9 patients (14.8%) (19.8%, including 3 atypical mutations), whereas k-ras oncogenic mutations were identified in six patients (9.8%); the EGFR positive rates is largely consistent with that observed for other lung cancers in East Asians (Ahn et al. 2008), and with the recently evaluated value (18%, 3 out of 17) in Japanese PPC patients (Kaira et al. 2010). However, the mutation rate found here is in contrast to results of Italiano et al., who reported that PPCs are characterized by a lack of EGFR mutation and a high rate of k-ras mutations (Italiano et al. 2009; Pelosi et al. 2004). It is well established that ethnic differences heavily affect EGFR etiology in lung cancer, and PPCs might be under similar ethnic influences in their ontogeny. In the present study, however, the distribution of EGFR mutation was not in line with the well-established phenomena. Namely, the EGFR mutations were detected, irrespective of clinicopathologic factors such as the component of adenocarcinoma, smoking status, and gender. Although this distribution of EGFR mutation can be explained in part by the specific characteristics of PPC, it should be cautious to interpret these data due to the small number of samples.

In the case of c-met, 11 patients demonstrated increased gene dosage; a c-met amplification and 10 high polysomies were detected using FISH. The c-met receptor tyrosine kinase has been associated with NSCLC as well as with SCLC (Chang et al. 2001; Jagadeeswaran et al. 2007; Maulik et al. 2002), suggesting that the c-met receptor may play an important role in cellular fate changes, including the epithelial to mesenchymal transition (Kubo et al. 2009; Salgia 2009). Increased c-met gene dosage was observed to be largely independent of EGFR and k-ras mutations in PPCs, positioning its blockade as an interesting monotherapy target.

Remarkably, the five genetic factors we have chosen to study in the analysis resulted in an unexpectedly high ratio of PPC samples detected with this defined probe set of genetic alterations. The fact that these patients who possess druggable or actionable molecular targets should be considered as candidates for mono or combinational targeted cancer therapy leads to an immediate clinical implication that warrants further validation in prospective clinical trials. Especially, EGFR mutation can be a possible predicitive marker for gefitinib or erlotinib and it is important to investigate where EGFR-TKI is effective for advanced PPC patients.

The molecular origin of PPC still remains largely obscure. It is the definition of a disease unit based on the histological observation, and whether there exists a singular genetic event leading to the emergence of this rare tumor type is still unknown. It is possible that a minute proportion of non-small-cell lung cancer will undergo a series of secondary genetic changes during the course of tumor evolution, reprogramming the cellular fates of primary tumors and propelling rare transitions in cellular fate through transdifferentiation or dedifferentiation. This re-directed cellular fate specification may culminate in histologically mixed cell populations observed in patient samples. The mutation profiling study presented here indicates that, at least, the oncogenic origins of this cancer type may be rather diverse, encompassing several well-known pulmonary oncogenic genetic factors.

The limitation of this study, as with many other mutation profiling studies, is that we can only detect a set of mutations in a subset of oncogenes with pre-established oncogenecity. Thus, other sets of mutations critical to the oncogenic process of PPCs might be missing in the analysis. Moreover, the percentages of these mutations detected from this preliminary screening that correspond to oncogenic or driver mutations need to be determined in future prospective studies. Given the rarity of this disease type, it will take a significant amount of time to accumulate sufficient clinical cases to properly determine the benefit the patients will experience from prospective oncogeno-chemo trials compared with that of histology-based conventional chemotherapeutics. To resolve this issue, further systemic and hypothesis-driven or a priori knowledge-free genomics-guided patient stratification is warranted in the laboratory to help more accurately describe each patient’s onco-genetics map. Until then, however, this preliminary attempt to characterize the mutational space of PPCs, previously thought to be an extremely malignant cancer type, will provide measurable molecular guidance to the alternative molecular treatment of this rare disease.

In summary, we have characterized the mutational statuses of several well-known oncogenic targets in a large set of PPC tumors. Given the diverse repertoire of mutational profiles observed from PPC samples, clinical trials based on accurate cancer-genotyping should be considered as a legitimate treatment scheme for this rare and hard-to-cure disease entity.