A Case of Small-Cell Lung Cancer With Novel Anaplastic Lymphoma Kinase Gene Rearrangement That Developed Intradural Extramedullary Spinal Metastases With Myelitis

Anaplastic lymphoma kinase (ALK) gene rearrangement-positive small-cell lung cancer (SCLC) is extremely rare. A 73-year-old man was diagnosed with SCLC. Standard treatments were not effective. Furthermore, at 74 years of age, intradural extramedullary metastases in the lumbar spinal cord and myelitis were observed. Autoimmune myelitis was suspected because anti-Zic4 antibodies were detected. However, steroid pulse therapy was ineffective. Interestingly, a novel ALK rearrangement of the isoamyl acetate hydrolyzing esterase 1 (IAH1)-ALK fusion gene was identified by blood-based next-generation sequencing. Although it was unclear whether the IAH1-ALK fusion gene was involved in tumor progression or an asymptomatic mutation, we treated the patient with alectinib, an ALK inhibitor; however, this therapy did not reduce the lesions. There is no established effective treatment for patients with SCLC who are ALK fusion gene positive by liquid biopsy. Therefore, patient-specific approaches and treatments are required.