Loss of 5 ' ALK leads to better response to crizotinib in sarcomas with ALK rearrangement.

e23554 Background: Crizotinib targets abnormal ALK activation, however, the clinical responses vary among patients with ALK rearrangement. A recent study showed that the NSCLC patients with 5'ALK loss have a favorable response to Crizotinib with doubled progression-free survival (PFS). We asked whether sarcoma patients with ALK rearrangement have a similar correlation between 5'ALK loss and clinical response to Crizotinib. Methods: The histopathologic diagnosis was made on H&E staining and IHC, including anti-ALK(D5F3). DNA isolated from FFPE materials was subjected to an NGS assay targeting 295 genes including ALK rearrangement. Results: 4 cases were detailed in Table. Case#1 is an inflammatory myofibroblastic tumor with a PLEKHH2-ALK rearrangement, which was previously reported in an NSCLC but not in sarcomas. Case #2 is an undifferentiated sarcoma with 2 ALK fusions, RANBP2-ALK and TMEM217-ALK, both in-frame fusions containing intact tyrosine kinase domains. The TMEM217-ALK is a novel fusion. Case#3 is a leiomyosarcoma with MYH9-ALK fusion, which was often seen in ALK-positive large B-cell lymphoma but not in sarcoma. Case #4 is an undifferentiated sarcoma with EML4-ALK fusion. All 4 cases had positive ALK IHC, consistent with the expression of ALK fusion proteins. Case#1 and #2 had a loss of 5' ALK, while case #3 and #4 retained the 5' ALK. All cases received and responded to Crizotinib therapy, with the Karnofsky Performance Status (KPS) improved from 30-60 score pre-therapy to 90-100 score after 3 months of Crizotinib. While Case#3 and #4, both retained the 5' ALK, relapsed at 9.4 m and 6.1 m, case#1 and #2, both lost 5' ALK, remain progression-free at 15m and 27m, respectively. The side effect was manageable with a grade II hepatic toxicity in only one patient. Conclusions: We report here 4 sarcomas with ALK rearrangement, including a novel fusion TMEM217-ALK. Two of these cases had a 5' ALK loss in addition to the 3' ALK rearrangement, and both had much longer PFS on Crizotinib therapy. The underlying mechanism deserved further investigation. Four fibrosarcomas with ALK rearrangements and their response to Crizotinib therapy.[Table: see text]