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D. Gonzalez De Castro
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P3.04 - Poster Session/ Biology, Pathology, and Molecular Testing (ID 235)
- Event: WCLC 2015
- Type: Poster
- Track: Biology, Pathology, and Molecular Testing
- Presentations: 1
- Moderators:
- Coordinates: 9/09/2015, 09:30 - 17:00, Exhibit Hall (Hall B+C)
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P3.04-011 - A Validation Study for the Use of ROS-1 Immunohistochemistry in Screening for ROS-1 Translocations in Lung Cancer (ID 2826)
09:30 - 09:30 | Author(s): D. Gonzalez De Castro
- Abstract
Background:
ROS-1 translocations are a rare genetic abnormality in lung cancers that, when identified, are a target for personalised therapy. The current test of choice is FISH, although with a rate of no more than 1-2%, screening using FISH is an expensive proposition. A further possibility is using immunohistochemistry (IHC) as a screening tool and commercial antibodies are now available that identify the ROS-1 protein in tumour cells. We present our data in undertaking a validation study for potential diagnostic usage.
Methods:
Given the relative rarity of the translocation and the fact the most driver mutations occur in isolation, a test cohort of cases was selected from patients recruited to phase 1 of the Cancer Research UK-Stratified Medicine Project (CRUK-SMP), who were identified as negative for EGFR, KRAS and/or BRAF mutations, as well as ALK translocations. Negative cases were then screened with an antibody for ROS-1 (D4D6, Cell Signalling, 1 in 300 dilution) and scored as negative, weakly positive or moderately positive, along with the percentage of positive cells. Cases were then sent for FISH analysis for the ROS-1 translocation, with a cut-off of > or = to15%, and the sensitivity and specificity of positive staining for ROS-1 was generated.
Results:
From 170 patients recruited from our institution into CRUK-SMP phase 1, a total of 103 patients were wild type for the above mutations (90 for all 4 genetic abnormalities. 9 further cases had failed tests for one and 4 for two mutations (6 carcinoids, 38 squamous cell carcinomas, 5 small cell carcinoma, 2 adenosquamous carcinoma, 1 pleomorphic carcinoma, 3 large cell carcinoma, 2 large cell neuroendocrine cell carcinoma, 7 non-small cell carcinoma (on biopsy) and 39 adenocarcinomas). 39 cases were tested (adenocarcinoma = 37, adenosquamous carcinoma = 2) with FISH, and one case was positive (78% positive cells). FISH testing was negative in 35 cases with scores of 1-8%, and three cases failed. The one positive case was positive on IHC (>90% of cells, moderate staining). In the 35 cases negative for FISH, four cases showed variable positivity on IHC (20, 40,50, 90%, moderate staining) and five cases showed weak focal staining (<5, <5, 10, 20, 30%, weak staining). The remainder were negative on IHC. All non-adenocarcinomas were negative on IHC. Several cases show positive staining of entrapped background pneumocytes and alveolar macrophages, making scoring problematic in some adenocarcinomas.
Conclusion:
Moderate staining for ROS-1 using IHC, independent of percentage positive cells, showed high sensitivity (100%) for tumours that contained a high level of translocated cells. However, specificity was at best 50%, even if a cut-off of 50% positive cells was applied. Pathologists also need to be aware of background staining so cases are not interpreted as false positives.
