Introduction: The anaplastic lymphoma kinase (ALK) fusion gene is expressed in 3%–5% patients with non-small cell lung cancer; targeting this gene with molecular targeted therapy results in a positive long-term prognosis. However, the ALK fusion gene expression rate is only 0.8% when restricted to pulmonary squamous cell carcinoma. Case Presentation: A 61-year-old non-smoking woman had undergone partial resection of the right lower lobe for lung adenocarcinoma 5 years previously, and ALK fusion gene positivity was confirmed at that time. Computed tomography (CT) revealed subcarinal lymph node enlargement. Subsequent positron emission tomography-CT imaging showed high uptake at this site and in the hepatic hilar lymph nodes. Subcarinal and hilar lymph node biopsies resulted in a diagnosis of squamous cell carcinoma. Squamous cell carcinoma of unknown primary was diagnosed because only metastatic lymph nodes were identified without a detectable primary lesion. Furthermore, the clinical presentation was considered inconsistent with metastatic recurrence, given the distinct histopathological difference from the initial surgical specimen and long disease-free interval. Treatment with carboplatin and paclitaxel was initiated. Although initial tumor reduction was achieved, the lesion subsequently progressed. After next-generation sequencing revealed ALK fusion gene positivity, the introduction of alectinib was effective. Conclusion: Alectinib is effective against ALK fusion gene-positive squamous cell carcinoma of unknown primary.
Kawakado et al. (2026) studied this question.