Transformation of ALK-positive NSCLC to SCLC after alectinib resistance and response to combined atezolizumab: a case report

Background: The genotypic and histological evolution of non-small cell lung cancer (NSCLC) to small cell lung cancer (SCLC) has been described as a mechanism of acquired resistance to epidermal growth factor receptor tyrosine kinase inhibitors (TKIs). However, it was extremely rare in anaplastic lymphoma kinase (ALK) positive NSCLC, and the follow-up care and outcomes of patients with this rare condition were unclear. This case was the first described the effectiveness of combined chemo-immunotherapy in a patient, with a transformed ALK positive NSCLC into SCLC after the administration of an ALK-TKIs.Case description: We described a unique case in which a patient with ALK-positive NSCLC underwent SCLC transformation at a metastatic site and remained ALK positive after TKI treatment. In July 2019, a 77-year-old man was diagnosed with ALK-positive stage IVB NSCLC, received alectinib and responded to alectinib. It was not until more than 7 months later that a cranial MRI showed brain metastases. And whole-brain radiotherapy was administered, and secondary epilepsy and metastatic progression occurred. One year later, computed tomography showed a left submandibular mass with multiple lymph node metastases, a left lower lung mass, and right pleura thickening. A left submandibular biopsy revealed SCLC. Echinoderm microtubule-associated protein-like 4-ALK (EML4-ALK) fusion and low tumor mutation burden (2.23 muts/Mb) were identified by next generation sequencing. The patient was administered atezolizumab (1,200 mg, d1) in combination with etoposide (0.13 g, d1-d3) and carboplatin (350 mg, d1). The left neck mass was reduced significantly, showing a partial response. Serum NSE (from 106 to 15 ng/mL), CA19-9 (from 49.4 to 34.6 U/mL) and CEA (from 4.18 to 3.09 ng/mL) returned to normal. Only mild myelosuppression (Grade 1), fatigue (Grade 1), and anorexia (Grade 1) were present. The patient had an overall survival time of 21 months.Conclusions: This case highlighted the importance of re-biopsies to reveal pathological SCLC transformation after ALK-TKI resistance, and suggested the treatment of atezolizumab in combination with etoposide and carboplatin were potentially helpful for this phenotype.