Determining the prevalence of ROS1 fusions in Chinese patients with non-small cell lung cancer

ROS1 fusions have no specific clinico-pathological features

A recent study found that ROS1 fusion-positive patients tended to be younger never smokers with a histologic diagnosis of adenocarcinoma. However, there is no evidence strong enough to support this finding as far due to a very low frequency of ROS1 fusions in non-small cell lung cancer (NSCLC). Additionally, ROS1 fusions were identified in squamous cell carcinoma histology, and moreover in several studies only some of ROS1 fusion-positive patients were never smokers.

Like EGFR mutation and EML4-ALK fusions, ROS1 fusions are shown to be essential for lung cancer development and serve as an effective therapeutic target of crizotinib in subgroups of populations.

To determine the prevalence and clinico-pathological features of ROS1 fusions in Chinese patients with NSCLC, a group of researchers from the Shanghai Pulmonary Hospital, Tongji University School of Medicine, Shanghai, China and Interdisciplinary Thoracic Oncology, University Medical Centre Mannheim, Heidelberg University, Mannheim, Germany screened formalin-fixed and paraffin-embedded (FFPE) tissue sections from 392 patients with NSCLC for ROS1 fusions by multiplex RT–PCR. All ROS1 fusions were validated by direct sequencing. The relationship between ROS1 fusions and clinico-pathological features and the prognostic effect of the ROS1 fusion status on survival were analysed.

In this study, published on 20 March 2013 as advance access article in the Annals of Oncology, 8 of 392 (2.0%) evaluable samples were found to harbour ROS1 fusions. Of the ROS1-positive patients, seven presented with adenocarcinoma, and one with adenosquamous carcinoma. The ratio of female to male and never smoker to smokers in a ROS1 fusion-positive group was 5:3. There was no statistically significant difference in age, sex, smoking history, histological type and pathological stage between ROS1 fusion-positive and ROS1 fusion-negative patients. ROS1 fusion-negative patients had a significantly longer survival when compared with ROS1 fusion-positive patients (p = 0.041). Lower pathological stage, younger age and ROS1 fusion-negative status were significantly associated with better prognosis on multivariate analysis.

ROS1 (also known as ROS, MCF3 or c-ros-1) is a proto-oncogene highly expressed in a variety of tumour cell lines. ROS1 protein is a type I integral membrane protein with tyrosine kinase activity and may serve as a growth or differentiation factor receptor. The ROS1 rearrangement rendering a constitutively active tyrosine kinase was first discovered in glioblastoma in 1987, then in NSCLC in 2007, and in cholangiocarcinoma and ovarian cancer in 2011.

Up to date, there are still some problems in the clinical application of fluorescence in situ hybridisation (FISH), including high costs, difficulty in interpretation and expertise required, although FISH is the unique diagnostic approach approved to screen for ALK rearrangement in NSCLC by FDA. Besides that, immunohistochemistry (IHC) is a cheap and widely used assay for fusion proteins; however, there has been no preferred antibody for identification of ROS1 fusion proteins to date. In addition to FISH and IHC, multiplex RT–PCR is an alternative method used to identify gene fusion in NSCLC.

A previous Chinese study detected two ROS1 fusion-positive cases from 202 East Asian never smokers with lung adenocaricnoma using RT–PCR and sequencing, with a prevalence of 1%. However, the study just designed primers for CD74-ROS1 and SLC34A2-ROS1 at that time, so it is very possible that some ROS1-positive patients with other fusion patterns were missed. The RT–PCR assay is highly sensitive, relatively cheap and easily widespread, and can determine specific fusion partners, although it cannot identify unknown variants.

The authors concluded that the prevalence of ROS1 fusions in NSCLC is low, even in Chinese patients. The ROS1-negative status is one of the three independent factors that are indicators of better prognosis. Additionally, with further research on fusion gene, the fusion patterns of ROS1 become increasingly complex. However, the authors questioned weather all patterns of ROS1 fusions, identified in NSCLC, serve as an oncogenic driver and have a similar sensitivity to ALK/ROS1 inhibitors. There is no definitive answer so far. Given the demonstrated good clinical efficacy of crizotinib in the treatment of NSCLC harbouring ROS1 fusions, this study provides new insights into the definition of the NSCLC population most likely to benefit from crizotinib in the absence of a standard diagnostic approach for NSCLC harbouring ROS1 fusions at present.

An expanded study on ROS1 fusions in Chinese NSCLC patients is ongoing.

This study was supported by grants from the National Natural Science Foundation of China (No. 81172101) and the key project of the Science and Technology Commission of Shanghai Municipality (No. 11JC1411301). The authors thanked Amoy Diagnostics CO., LTD. (Xiamen, China) for technical support.