Screening for ROS1 gene rearrangements in non-small-cell lung cancers using immunohistochemistry with FISH confirmation is an effective method to identify this rare target.
OBJECTIVE
To assess the prevalence of ROS1 rearrangements in a retrospective and prospective diagnostic Australian cohort and evaluate the effectiveness of immunohistochemical screening.


RESULTS
A retrospective cohort of 278 early stage lung adenocarcinomas and an additional 104 prospective non-small-cell lung cancer (NSCLC) cases referred for routine molecular testing were evaluated. ROS1 immunohistochemistry (IHC) was performed (D4D6 clone, Cell Signaling Technology) on all cases as well as fluorescence in-situ hybridization (FISH) using the ZytoVision and Abbott Molecular ROS1 FISH probes, with ≥15% of cells with split signals considered positive for rearrangement. Eighty-eight cases (32%) from the retrospective cohort showed staining by ROS1 IHC, and one case (0.4%) showed ROS1 rearrangement by FISH. Nineteen of the prospective diagnostic cases showed ROS1 IHC staining, 12 (12%) cases of which were confirmed as ROS1 rearranged by FISH. There were no ROS1 rearranged cases that showed no expression of ROS1 with IHC. The ROS1 rearranged cases in the prospective cohort were all EGFR wild-type and anaplastic lymphoma kinase (ALK) rearrangement-negative. The sensitivity of ROS1 IHC in the retrospective cohort was 100% and specificity was 76%.


CONCLUSIONS
ROS1 rearrangements are rare events in lung adenocarcinomas. Selection of cases for ROS1 FISH testing, by excluding EGFR/ALK-positive cases and use of IHC to screen for potentially positive cases, can be used to enrich for the likelihood of identifying a ROS1 rearranged lung cancer and prevent the need to undertake expensive and time-consuming FISH testing in all cases.
Tissue Pathology and Diagnostic Oncology, Royal Prince Alfred Hospital, Camperdown, NSW, Australia.
Christina I
CI
Selinger
Department of Medical Oncology, Royal North Shore Hospital, St Leonards, NSW, Australia.|Thoracic Oncology Service, Memorial Sloan Kettering Cancer Center, New York, USA.|Sydney Medical School, University of Sydney, Camperdown, NSW, Australia.
Bob T
BT
Li
Department of Medical Oncology, Royal North Shore Hospital, St Leonards, NSW, Australia.|Sydney Medical School, University of Sydney, Camperdown, NSW, Australia.
Nick
N
Pavlakis
Department of Medical Oncology, St George Hospital, Kogarah, NSW, Australia.
Matthew
M
Links
Sydney Medical School, University of Sydney, Camperdown, NSW, Australia.|Cancer Diagnosis and Pathology Group, Kolling Institute of Medical Research, Royal North Shore Hospital, St Leonards, NSW, Australia.
Anthony J
AJ
Gill
Department of Medical Oncology, Royal North Shore Hospital, St Leonards, NSW, Australia.
Adrian
A
Lee
Department of Medical Oncology, Royal North Shore Hospital, St Leonards, NSW, Australia.|Sydney Medical School, University of Sydney, Camperdown, NSW, Australia.
Stephen
S
Clarke
Tissue Pathology and Diagnostic Oncology, Royal Prince Alfred Hospital, Camperdown, NSW, Australia.
Thang N
TN
Tran
Tissue Pathology and Diagnostic Oncology, Royal Prince Alfred Hospital, Camperdown, NSW, Australia.
Trina
T
Lum
The Kinghorn Cancer Centre, Garvan Institute of Medical Research, Darlinghurst, NSW, Australia.|School of Medicine, University of Western Sydney, Sydney, NSW, Australia.|Chris O'Brien Lifehouse, Camperdown, NSW, Australia.|Macarthur Cancer Therapy Centre, Campbelltown Hospital, Camperdown, NSW, Australia.
Po Y
PY
Yip
Sydney Medical School, University of Sydney, Camperdown, NSW, Australia.|The Kinghorn Cancer Centre, Garvan Institute of Medical Research, Darlinghurst, NSW, Australia.|Medical Oncology, Royal Prince Alfred Hospital, Camperdown, NSW, Australia.
Lisa
L
Horvath
Sydney Medical School, University of Sydney, Camperdown, NSW, Australia.|Department of Medical Genomics, Royal Prince Alfred Hospital, Camperdown, NSW, Australia.
Bing
B
Yu
The Kinghorn Cancer Centre, Garvan Institute of Medical Research, Darlinghurst, NSW, Australia.|School of Medicine, University of Western Sydney, Sydney, NSW, Australia.|St Vincent's Clinical School, University of New South Wales, Darlinghurst, NSW, Australia.
Maija R J
MR
Kohonen-Corish
Tissue Pathology and Diagnostic Oncology, Royal Prince Alfred Hospital, Camperdown, NSW, Australia.|Sydney Medical School, University of Sydney, Camperdown, NSW, Australia.|The Kinghorn Cancer Centre, Garvan Institute of Medical Research, Darlinghurst, NSW, Australia.
Sandra A
SA
O'Toole
Tissue Pathology and Diagnostic Oncology, Royal Prince Alfred Hospital, Camperdown, NSW, Australia.|Sydney Medical School, University of Sydney, Camperdown, NSW, Australia.|School of Medicine, University of Western Sydney, Sydney, NSW, Australia.
Wendy A
WA
Cooper
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D014408:Biomarkers, Tumor / Q000032:analysis* / Q000235:genetics; D002289:Carcinoma, Non-Small-Cell Lung / Q000235:genetics*; D005260:Female; D015321:Gene Rearrangement; D006801:Humans; D007150:Immunohistochemistry; D017404:In Situ Hybridization, Fluorescence; D008175:Lung Neoplasms / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D011505:Protein-Tyrosine Kinases / Q000235:genetics*; D011518:Proto-Oncogene Proteins / Q000235:genetics*
D014408:Biomarkers, Tumor; D011518:Proto-Oncogene Proteins; D011505:Protein-Tyrosine Kinases; C062333:ROS1 protein, human
c-ros oncogene 1 (ROS1); fluorescence in-situ hybridization (FISH); immunohistochemistry (IHC); non-small-cell lung cancer (NSCLC)