Case Report: Early Distant Metastatic Inflammatory Myofibroblastic Tumor Harboring Fusion Gene: Study of Two Typical Cases and Review of Literature.

Inflammatory myofibroblastic tumor (IMT) is a distinctive neoplasm that frequently arises in the lung and accounts for ~1% of lung tumors. Distant metastatic IMT is extremely rare and has been poorly investigated. This analysis was specifically performed to explore the clinicopathological and genetic features of early distant metastatic IMT. Two typical patients with distant metastatic IMTs were selected, which accounted for 1.13% of all diagnosed IMTs in the last 5 years. One patient was a 55 year-old male, and the other patient was a 56 year-old female. Both primary tumors arose from the lung, and the initial clinical symptoms of the two patients involved coughing. Both of the imaging examinations showed low-density nodular shadows in the lungs with enhancement around the mass. Microscopically, dense arranged tumor cells, prominent cellular atypia, and high mitotic activity with atypical form were more prominent in the metastatic lesions than in the primary lesions. All of the primary and metastatic tumors in both cases showed positive anaplastic lymphoma kinase () immunostaining and rearrangement fluorescence hybridization. The (exon 6) (exon 20) fusion variant (v3a/b) was identified by using next-generation sequencing (NGS) and was verified by using reverse transcription polymerase chain reaction (RT-PCR). Furthermore, intronic variants of and synonymous variants of were also detected NGS in one IMT for the first time and were verified in all of the primary and metastatic lesions PCR. Distant metastasis occurred during a short period of time (1 and 2 months) after the first surgery. One patient presented with multiple metastases to the subcutaneous tissue and bone that responded to inhibitor alectinib therapy, and the tumor was observed to regress 10 months after the initial inhibitor therapy. In contrast, the other patient presented with subcutaneous neck metastasis without inhibitor treatment and succumbed to the disease within 3 months after the surgery. This study demonstrated the possible role of -v3a/b in the malignant progression of IMT and proposed certain therapeutic effects of inhibitors on multiple metastatic IMTs.