This article reports a case of advanced metastatic low-grade sarcoma. The patient was diagnosed with an inoperable large (14 × 12 cm) lesion on his neck in September 2015 and underwent two ineffective chemotherapies in the following 4 months. Interestingly, although several pathologists could not agree on the histopathological diagnosis, the precise molecular pathological diagnosis was obtained using next-generation sequencing (NGS) and finally brought excellent therapeutic effects. The patient was detected to have CARS-ALK fusion by NGS and then was successfully treated with crizotinib orally. He received surgical resection of primary and metastatic lesions after tumor shrinkage. The combined treatment brought a durable response for 40 months. Although the tumor recurred in July 2019, the patient has been responding well to the second-line ALK tyrosine kinase inhibitor alectinib to date. We performed whole genome sequencing on the patient's primary, metastatic, and recurrent tumors and did comprehensive genomic analysis. Furthermore, our analysis results revealed that a whole genome duplication event might have happened during tumorigenesis of this case. KEY POINTS: To our best knowledge, this is the first report of a very successful treatment with first- and second-line ALK tyrosine kinase inhibitors for CARS-ALK fusion-positive metastatic low-grade sarcoma. Molecular pathological result can guide precision treatment for sarcoma, even when the exact histopathology cannot be obtained. Multiple samples from this patient were analyzed using whole genome sequencing. Results provided detailed genomic characteristics and showed tumor evolution of this low-grade sarcoma case. A whole genome duplication event might have happened during tumorigenesis of this low-grade sarcoma case.
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