The absence of a novel intron 19-retaining ALK transcript (ALK-I19) and MYCN amplification correlates with an excellent clinical outcome in neuroblastoma patients

// Abdulraheem Alshareef 1, 2 , Meredith S. Irwin 3 , Nidhi Gupta 2 , Hai-Feng Zhang 2, 4 , Moinul Haque 2 , Scott D. Findlay 5, 6 , Bo Kyung Alex Seong 7 , Justine Lai 2 , Mohammed Rayis 8 , Sadeq Al-Dandan 9 and Raymond Lai 2, 5, 10 1 Department of Applied Medical Sciences, Taibah University, Medina, Saudi Arabia 2 Department of Laboratory Medicine and Pathology, University of Alberta, Edmonton, Canada 3 Division of Haematology-Oncology, Department of Pediatrics, The Hospital for Sick Children, University of Toronto, Ontario, Canada 4 Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, Canada 5 Department of Oncology, University of Alberta, Edmonton, Canada 6 Department of Anatomy and Cell Biology, Faculty of Medicine and Dentistry, University of Western Ontario, London, Canada 7 Department of Medical Biophysics, University of Toronto, Toronto, Canada 8 Department of Pediatric Oncology, King Fahad Medical City, Riyadh, Saudi Arabia 9 Department of Anatomical Pathology, King Fahad Medical City, King Saud bin Abdulaziz University, Riyadh, Saudi Arabia 10 DynaLIFE Medical Laboratories, Edmonton, Canada Correspondence to: Raymond Lai, email: rlai@ualberta.ca Keywords: neuroblastoma; anaplastic lymphoma kinase; alk-expressing human cancers; intron-retention transcript; prognostic markers Received: January 04, 2017      Accepted: December 28, 2017      Published: January 12, 2018 ABSTRACT ALK missense mutations are detected in 8% of neuroblastoma (NB) tumors at diagnosis and confer gain-of-function oncogenic effects. The mechanisms by which the expression of wild-type or mutant ALK , which is detectable in the majority of cases, is regulated are not well understood. We have identified a novel ALK transcript characterized by the retention of intron 19 ( ALK-I19 ). ALK-I19 was detected in 4/4 NB cell lines, but not other non-NB cells with ALK aberrations. The functional significance of ALK-I19 was determined by specific siRNA knockdown of this transcript, which resulted in substantially decreased expression of the fully-spliced ALK transcripts (FS- ALK ) and a significant reduction in cell growth. We also demonstrate that ALK-I19 is a precursor of FS- ALK . ALK-I19 was detected in 14/37 (38%) tumors from patients with newly diagnosed NB. ALK-I19 expression correlated with undifferentiated histology and strong ALK protein expression detectable by immunohistochemistry. Importantly, patients with tumors that did not express ALK-I19 and lacked MYCN amplification had an excellent clinical outcome, with 19/19 patients survived at 5-years. In conclusion, ALK-I19 is a novel ALK transcript that likely represents a marker of undifferentiated NB cells. The absence of ALK-I19 and MYCN amplification is a useful prognostic marker for NB patients.