The Significance Of ROS1 Rearrangements In Pulmonary Non-Small Cell Carcinomas

By Bahram Robert Oliai, M.D.,


In this issue of the ProPath Focus I would like to share some extremely exciting developments in the treatment of patients with pulmonary non-small cell carcinoma.

Lung cancer is still the leading cancer related killer worldwide, with non-small cell (NSCLC) types accounting for the vast majority of cases (85%). The discovery of EGFR mutations and ALK gene rearrangements in a subset of these tumors has created opportunities for customized therapy with drugs such as erlotinib and genfitinib (for those with EGFR mutations) and crizotinib (for those with ALK rearrangements). In those patients whose tumors harbor these mutations, clinicians are now specifically and often highly effectively attacking these killers with drugs targeted to their genetic aberrations. For that reason, it is critical to identify those patients whose lung cancers have these mutations, so that the best possible treatment outcomes can be achieved.

ROS1 is a receptor tyrosine kinase of the insulin receptor family which is phylogenetically related to ALK. ROS1 rearrangements have previously been reported in glioblastoma cell lines, cholangiocarcinomas, and ovarian serous tumors of low malignant potential. More recently, ROS1 fusions have been identified as a driver mutation in a non-small carcinoma cell line (HCC78) which led to the discovery that NSCLC with ROS1 fusions demonstrate sensitivity to crizotinib (the same drug used to treat ALK rearrangement positive NSCLC). Interestingly ALK and ROS1 appear to be mutually exclusive rearrangements (such that NSCLC with one will not have the other). 

There are many features which shared by ALK and ROS1 rearranged NSCLC. Much like ALK, ROS1 positive tumors are very rare accounting for only between 1.2-2.5% of NSCLC tested. ROS1 fusions tended to be more common in younger female patients who have never smoked. Additionally those of East Asian descent and with stage IV disease were overrepresented. Virtually all of the tumors where shown to be adenocarcinomas with a subset demonstrating morphologic features previously described in ALK positive tumors such as signet ring cell features and mucinous cribriform histology1,2,7.


Although treatment data is currently somewhat limited, it is promising. Crizotinib has demonstrated in vitro activity against the ROS1 positive cell line HCC78 and one study of 14 such patients reported a response rate of 57% with a disease control rate of 79% at 8 weeks2. More remarkable are the results achieved in one 31 year old (who never smoked) with multifocal bronchioloalveolar carcinoma. This patient was hypoxic at the time therapy was initiated. At 8 weeks of treatment his scans demonstrated near complete resolution of his tumor, with no evidence of recurrence at 6 months on crizotinib!1

Given the rarity of ROS1 rearrangements, the observation that ROS1 rearrangement positive tumors are ALK negative, and the potential similar treatment response with crizotinib, it would seem that testing for ROS1 should be performed for all patients with NSCLC who would currently tested for tested for ALK. Fortunately at ProPath we are now able to offer testing for ROS1 rearrangements using a highly specific and sensitive break apart FISH probe set (Fig 1). In addition, an immunostain for ROS1 is available (clone D4D6, Fig 2) that shows excellent correlation with results by FISH4.

One possible testing strategy would be to screen all pulmonary adenocarcinomas submitted for ALK testing with the ROS1 (D4D6) immunostain and follow-up any positive cases with the FISH test for ROS1 rearrangements. I am proud to say that we have successfully optimized the immunostain assay and validated the FISH results in our laboratory and we are excited to offer these tests for your patients with the superior quality and rapid immunostain turnaround time for which ProPath is famous.



I would like to thank Debra Cohen, BS, CG(ASCP)CM of the ProPath FISH laboratory for calling ROS1 to my attention.



1. Bergethon K, Shaw AT, Ou SHI et al. ROS1 Rearrangements Define a Unique Molecular Class of Lung Cancers. Journal of Clinical Oncology 2012; 30(8): 863-870.

2. Chin LP, Soo RA, Soong R et al. Targeting ROS1 with Anaplastic Lymphoma Kinase Inhibitors A Promising Therapeutic Strategy for a Newly Defined Molecular Subset of Non-Small-Cell Lung Cancer. Journal of Thoracic Oncology 2012; 7(11): 1625-1630.

3. Davies KD, Le AT, Theodoro MF et al. Identifying and Targeting ROS1 Gene Fusions in Non-Small Cell Lung Cancer. Clinical Cancer Research 2012; 18(17):4570-4579.

4. Rimkunas VM, Crosby KE, Li D et al. Analysis of Receptor Tyrosine Kinase ROS1-Positive Tumors in Non-Small Cell Lung Cancer: Identification of a FIG-ROS1 Fusion. Clinical Cancer Research 2012; 18(16): 4449-4457.

5. Stumpfova M, Janne PA. Zeroing in on ROS1 Rearrangements in Non-Small Cell Lung Cancer. Clinical Cancer Research 2012; 18(16): 4222-4224.

6. Yasuda H, de Figueiredo-Pontes, Kobayashi, Costa DB. Preclinical Rationale for the Use of the Clinically Available Multitargeted Tyrosine Kinase Inhibitor Crizotinib in ROS1-Translocated Lung Cancer. Journal of Thoracic Oncology 2012; 7(7): 1086-1090.

7. Yoshida A, Kohno T, Tsuta K et al. ROS1-Rearranged Lung Cancer A Clinicopathologic and Molecular Study of 15 Surgical Cases. American Journal of Surgical Pathology 2013; 00(00): 1-9.