ALK Rearrangement in Small-Cell Lung Cancer and Durable Response to Alectinib: A Case Report

Background: With the development of next-generation sequencing (NGS), several anaplas-tic lymphoma kinase (ALK) fusion partner genes have been identified. However, ALK fusion is extremely rare in small cell lung cancer (SCLC), and there is no standard treatment option. Here, we report a patient with SCLC who carried an ALK- Intergenic Region (IR) rearrange-ment and responded to Alectinib. Case Presentation: A 26-year-old man was pathologically diagnosed with extensive-stage SCLC. After 2 cycles of first-line chemotherapy, CT showed a large soft tissue mass in the middle lobe of the right lung and increased liver nodules, left kidney lesions and right kidney lesions. To seek potential therapeutic regimens, ALK rearrangement was identified. The patient achieved a rapid and durable partial response with Alectinib (600 mg BID). The patient experienced a significant clinical response with a progression-free survival of more than 6 months. There were no grade 3 or more adverse events reported, and there was no dose reduction during treatment. Following Alectinib treatment, the allele frequency of ALK rearrangement and RB1 and TP53 mutations in plasma circulating tumor DNA decreased with the reduction in tumor size. Conclusion: This case provides a meaningful reference for the treatment of SCLC patients with ALK rearrangement. This case also provides valuable information on the response to ALK inhibitors in patients with ALK-IR rearrangement and better understanding of ALK-TKI applications in the future.