Background: The EML4-ALK fusion gene has recently been identified as a driver mutation in a subset of non-small cell lung cancers. In subsequent studies, EML4-ALK has been detected in a low percentage of patients, and was associated with a lack of EGFR or KRAS mutations, younger age, and adenocarcinoma with acinar histology. Cases with the EML4-ALK fusion gene were examined to clarify the clinicopathological characteristics of young adenocarcinoma patients. Methods: Between December 1998 and May 2009, 85 patients aged ≤ 50 with lung adenocarcinoma were treated at our hospital. We examined 49 samples from adenocarcinoma patients who underwent surgical resection, chemotherapy, and/or radiotherapy for the EML4-ALK gene. None of the patients received ALK inhibitors because these drugs had not been approved in Japan before 2012. EML4-ALK fusion genes were screened using multiplex reverse-transcription PCR assay, and were confirmed by direct sequencing. Results: The EML4-ALK fusion gene was detected in five tumors (10.2%). One patient had stage IB disease, one had stage IIIA, and three had stage IV. Histologically, there was one solid adenocarcinoma, two acinar adenocarcinomas, and two papillary adenocarcinomas. EML4-ALK fusion genes were mutually exclusive to EGFR and KRAS mutations. The five-year survival rate was 59.4% in patients without EML4-ALK fusion and was not reached in patients with EML4-ALK fusion. Conclusion: The EML4-ALK fusion gene may be a strong oncogene in younger patients with lung adenocarcinoma.
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