EPR17341 and A7H6R pan-TRK Immunohistochemistry Result in Highly Different Staining Patterns in a Series of Salivary Gland Tumors

Abstract

Patients with NTRK-rearranged tumors can be now treated using anti-TRK–targeted therapies making NTRK testing important for treatment choices in patients with advanced cancers. Pan-TRK immunohistochemistry (IHC) could be a valuable premolecular screening strategy in this field. The choice of 1 IHC method or another requires to investigate for intermethod comparison. A high frequency of pan-TRK positive tumors among salivary gland tumors makes these tumors particularly appropriate for such a technical study. In this work, we studied the intermethod agreement for 2 pan-TRK IHC methods (using A7H6R and EPR17341 clones) in a file of salivary gland tumors of different subtypes. Among 71 tumors, pan-TRK IHC was diagnosed as positive (ie, H score ≥5) in 23 and 18 cases using EPR17341 and A7H6R clones, respectively, with a good intermethod agreement in terms of positive/negative result (κ, 0.70) but only a moderate agreement considering the H score values themselves (intraclass correlation coefficient of 0.5399). Beyond the intensity of staining and the percentages of stained cells, major differences were also observed between the location and type of cells stained in positive cases between the 2 clones. The single NTRK-rearranged case in our series (ie, a NTRK3-rearranged salivary secretory carcinoma) was positive with the 2 pan-TRK antibodies. Future studies including molecularly proven NTRK-rearranged tumors remain required to further study and compare the performances of different pan-TRK clones in the screening of NTRK-rearranged cancers but it is now obvious that the staining patterns of A7H6R and EPR17341 clones are not strictly identical.

Pan-TRK Immunohistochemistry: An Example-Based Practical Approach to Efficiently Identify Patients With NTRK Fusion Cancer

“…44,45 Pan-TRK IHC usually shows nuclear staining with a TTF-1-like or silver in situ hybridization-like staining pattern, associated with a weak cytoplasmic positivity in 100% of the cells (Figure 5, B). Although nuclear pan-TRK IHC is very specific, 29,46 pathologists should be aware of several facts: (1) cytoplasmic staining alone has also been described at a lower frequency in larger series, 46,47 and unfortunately this cytoplasmic pattern can also be found in many other benign and malignant salivary gland neoplasms (see below) 29, [46][47][48] ; and (2) the nuclear pan-TRK staining can be weak and/or focal, 29,46,47 and a suboptimal sensitivity of pan-TRK IHC for NTRK3-rearranged tumors has been suggested. 14…”

“…14 At least 40% of adenoid cystic carcinomas can show moderate to strong cytoplasmic staining in the outer layer of tumor cells (Figure 11, B), which never corresponds to an NTRK fusion. 14,48 Interestingly, adenoid cystic carcinomas can also show overexpression of KIT and EGFR, which are rarely mutated or amplified, further preventing druggable opportunities. 44…”

Detection of NTRK1/3 Rearrangements in Papillary Thyroid Carcinoma Using Immunohistochemistry, Fluorescent In Situ Hybridization, and Next-Generation Sequencing

“…However, these methodologies may be compromised by suboptimal RNA quality of the formalin-fixed paraffin-embedded (FFPE) tissue, high labor demand, and high cost. Recently, the application of immunohistochemistry (IHC) using antipan-TRK antibody to detect NTRK gene fusions in various tumor types has been widely discussed and mainly focused on secretory carcinoma of the salivary gland and soft tissue tumors [7][8][9][10][11][12][13][14][15][16][17][18]. PTC was included in only two of studies with a limited number of cases [19,20].…”

Immunohistochemistry as a screening tool for NTRK gene fusions: results of a first Belgian ring trial

“…In a recent study by Guibourg et al, a total of 71 salivary gland tumours were stained with the two pan-TRK IHC antibody clones. Only one case was fusion-positive, and this NTRK3-rearranged salivary secretory carcinoma was found to be positive with both the EPR17341 and the A7H6R clone [27]. Finally, in a large cohort of over 4000 colorectal cancer samples, both antibodies demonstrated similar staining characteristics and showed diffuse strong cytoplasmic staining in all nine fusion-positive cases.…”