IHC Staining Found Effective for ROS1+ NSCLC

The use of immunohistochemistry (IHC) could be a more cost- and time-efficient first-line screening method for identifying ROS1 gene rearrangements to predict eligibility for crizotinib (Xalkori) for patients with non—small cell lung cancer (NSCLC) compared with fluorescence in-situ hybridization (FISH), according to results of a trial recently published in the Journal of Thoracic Oncology.

FISH has been used as the standard screening method for identifying ROS1 gene rearrangements, which occurs in approximately 1% to 2% of NSCLC cases. Currently, FISH screening is recommended in all NSCLC cases to detect ALK translocations or EGFR, KRAS, and BRAF mutations; however, following results of the study, the researchers implied that IHC could be an improved option.

“This study confirms that IHC staining for ROS1 protein within the cytoplasm of tumor cells can potentially be used as a screening tool for ROS1 gene rearrangements,” lead author Patrizia Viola, MD, and colleagues wrote. “With a high sensitivity rate and relatively high specificity rate, IHC screening to identify patients who might harbor ROS1 gene rearrangements is feasible and would be less expensive and time-consuming than FISH testing, which could be reserved for a confirmatory second step.”

The phase I trial of the Cancer Research UK-Stratified Medicine Project (CRUK-SMP) screened 170 patients with lung tumors to determine the sensitivity and specificity of IHC staining in the detection of ROS1 gene rearrangements. Tissue samples were tested with the ROS1 D4D6 antibody using two approaches, the Dako EnVision IHC system and FISH analysis.

The results of the IHC screening were scored as negative or weakly, moderately, or strongly positive for the ROS1 gene rearrangement and were measured for the percentage of positive cells, with an h-score above 100 considered to be ROS1-positive.

Among the lung tumor cohort, 103 of 170 patients (61%) were further analyzed, following negative testing for EGFR, KRAS, BRAF, and ALK. Further testing discovered the group consisted of 39 adenocarcinomas, 39 squamous cell carcinomas, 5 small cell carcinomas, 2 adenosquamous carcinomas, 3 pleomorphic carcinomas, 4 large cell carcinomas, 2 large cell neuroendocrine cell carcinomas, 3 NSCLC, and 6 carcinoids. All histologies, except for adenocarcinoma, tested negative for ROS1 rearrangements.

In the adenocarcinoma subgroup, IHC screening identified ROS1 expression on 5 samples, with 2 marked as ROS1-positive using the h-score cutoff. FISH analysis identified 1 of 2 as positive for ROS1. An additional 5 samples were marked as weakly positive for ROS1.

Four additional cases were identified as ROS1-positive using IHC from the diagnostic archive, for a larger pool of evaluable patients. In this larger group, IHC staining proved to be 100% sensitive (95% CI, 48-100) and 83% specific (95% CI, 86-100) for the detection of ROS1-positive rearrangements.

Patients with ROS1 gene rearrangements were typically younger and non-smokers compared with the rest of the study pool. Each of their tumors were adenocarcinomas. Four patients showed a partial response to crizotinib and 3 showed a partial response to pemetrexed. Of these, 3 of 4 patients were still alive at 13, 27, and 31 months, respectively.

“The main limitation of the study is that the number of cases proving positive for the ROS1 gene rearrangement was low, necessitating enrichment from the diagnostic archive to support the high level of sensitivity,” Viola, with the Department of Histopathology, Royal Brompton and Harefield National Health Service Foundation Trust, London, United Kingdom, and co-authors wrote.

The FDA approved crizotinib, a tyrosine kinase inhibitor initially approved for treatment of ALK-positive NSCLC, for the treatment of ROS1-positive NSCLC earlier this year. Due to the rarity of ROS1-positive NSCLC cases, an accurate and cost-effective method is required for the screening of ROS1 gene rearrangements, which would lead to a more personalized treatment selection, such as in the use of crizotinib for ROS1-positive NSCLC.

Viola P, Maurya M, Croud J, et al. A validation study for the use of ROS1 immunohistochemical staining in screening for ROS1 translocations in lung cancer [Published online May 11, 2016]. J Thorac Oncol. doi: 10.1016/j.jtho.2016.03.019