An Inflammatory Myofibroblastic Tumor With a Novel ALK Mutation Leading to Acquired Resistance to Tyrosine Kinase Inhibitors.

Inflammatory myofibroblastic tumor (IMT) is a rare mesenchymal neoplasm that can locally recur and potentially metastasize. Approximately 50% of IMTs harbor rearrangements in the gene encoding anaplastic lymphoma kinase (ALK), a receptor tyrosine kinase that can be therapeutically targeted with tyrosine kinase inhibitors (TKIs). With successful application of TKI in ALK-positive nonsmall cell carcinoma (NSCLC), ALK inhibitors are often first-line treatments for patients with unresectable or metastatic IMTs. Although acquired resistance to these agents may develop, resistance mechanisms are sparsely reported for IMTs. Here we report a case of a 71 year-old man with metastatic pulmonary IMT harboring a DCTN1::ALK fusion that progressed during alectinib TKI treatment. Whole exome sequencing of an enlarging metastatic lesion in right 4th rib revealed a novel p.V1180L mutation in the ALK tyrosine kinase domain as the mechanism of acquired resistance. To our knowledge, this is the first report of acquired p. V1180L mutation in IMTs treated with TKIs. In cases of ALK-positive IMTs that progress on TKI therapy, targeted sequencing for acquired ALK mutations may inform clinical decisions to adopt second-line therapeutic strategies.