Fu Yao, Li Zheng, Gao Fuping, Yang Jun, Wu Hongyan, Zhang Biao, Pu Xiaohong, Fan Xiangshan
Department of Pathology, Nanjing Drum Tower Hospital, The Affiliated Hospital of Nanjing University Medical School, Nanjing, China.
Ningbo Diagnostic Pathology Center, Ningbo, China.
Front Oncol. 2021 Apr 29;11:669197. doi: 10.3389/fonc.2021.669197. eCollection 2021.
To gain insight into the clinicopathologic profile of colorectal carcinomas harboring oncogenic NTRK fusions based on eastern populations as well as make the best testing algorithm for the screen, we use pan-Trk immunohistochemistry (IHC), fluorescence hybridization (FISH) respectively to screen NTRK fusions in a large, unselected cohort of 819 colon cancers; either IHC or FISH positive cases were further detected by next-generation sequencing (NGS). IHC staining was observed in ten (1.22%) cases. FISH positive was observed in 13 (1.59%) cases, and finally, a total of 18 cases were under both a DNA-based and an RNA-based NGS assay. RNA-based NGS was positive in 13 of 18 cases, whereas DNA-based NGS was only positive in three of 18 cases. In total 13 RNA-based NGS NTRK fusion-positive cases, only six cases were pan-TRK IHC positive 12 were FISH positive. More important, in 13 RNA-based NGS cases only five cases contain the full length of NTRK tyrosine kinase (TK) domain and form the classical fusion chimeras, other six cases only maintain parts of the TK domain and form the sub-classical fusion chimeras, two cases totally miss the TK domain and form the non-classical fusions. For clinicopathologic characteristics, besides the MMR (mismatch repair) status (p = 0.001), there is no difference between the NTRK fusion-positive and negative cases. Nevertheless, classical fusion cases prefer low differentiation (p = 0.001) and different patterns of growth (p < 0.001). Besides, we found all five classical NTRK fusion cases, and only one sub-classical case was harboring MLH1/PMS2 deficiency. When combining FISH and MMR (Mismatch Repair) status, besides one sub-classical case, all five classical fusions were detected, which means MLH1/PMS2 expression could further narrow the classical fusions in FISH NTRK fusion positive cases. Given the low sensitivity and specificity of the pan-Trk antibody, it would be useless to use IHC to screen NTRK fusion-positive CRCs. Combining FISH and MLH1/PMS2 IHC would be a good testing algorithm for the screen effective NTRK fusions. Finally, if patients are going to undergo TRK-based targeted therapy, only RNA-based NGS for detection of the specific fusion could tell the precise rearrangement information.
为深入了解基于东方人群的携带致癌性NTRK融合的结直肠癌的临床病理特征，并制定最佳的筛查检测算法，我们分别使用泛TRK免疫组织化学（IHC）、荧光原位杂交（FISH）对819例未经选择的结肠癌大样本队列进行NTRK融合筛查；免疫组化或FISH阳性的病例进一步通过二代测序（NGS）检测。10例（1.22%）观察到免疫组化染色阳性。13例（1.59%）观察到FISH阳性，最终，共有18例接受了基于DNA和基于RNA的NGS检测。基于RNA的NGS在18例中有13例呈阳性，而基于DNA的NGS在18例中仅3例呈阳性。在总共13例基于RNA的NGS检测NTRK融合阳性的病例中，仅6例泛TRK免疫组化阳性，12例FISH阳性。更重要的是，在13例基于RNA的NGS病例中，仅5例包含全长NTRK酪氨酸激酶（TK）结构域并形成经典融合嵌合体，另外6例仅保留部分TK结构域并形成亚经典融合嵌合体，2例完全缺失TK结构域并形成非经典融合。对于临床病理特征，除错配修复（MMR）状态外（p = 0.001），NTRK融合阳性和阴性病例之间无差异。然而，经典融合病例更倾向于低分化（p = 0.001）和不同的生长模式（p < 0.001）。此外，我们发现所有5例经典NTRK融合病例中，只有1例亚经典病例存在MLH1/PMS2缺陷。当结合FISH和MMR（错配修复）状态时，除1例亚经典病例外，所有5例经典融合均被检测到，这意味着MLH/PMS2表达可进一步缩小FISH检测NTRK融合阳性病例中的经典融合范围。鉴于泛TRK抗体的低敏感性和特异性，使用免疫组化筛查NTRK融合阳性的结直肠癌是无用的。结合FISH和MLH1/PMS2免疫组化将是一种有效的筛查NTRK融合的检测算法。最后，如果患者要接受基于TRK的靶向治疗，只有基于RNA的NGS检测特定融合才能提供精确的重排信息。
