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Patients with smoking-independent lung cancer mainly consist of females, yet the molecular background of this epidemiological feature, other than epidermal growth factor receptor (EGFR) mutation, remains unclear. Several studies have revealed the association between female hormone-associated factors and the prognosis of lung cancer, however the data remain inconsistent. The present study focused on the expression of estrogen receptor (ER)α in order to elucidate this association in smoking-independent lung cancer. Immunohistochemistry staining (IHC) of aromatase, ERα and ERβ was performed against formalin-treated tissues from 38 patients who had never-smoked who underwent complete surgical resection between 2012 and 2013. Among them, adequate RNA of the tumor and adjacent normal lung cancer was extracted from 31 matching deep frozen samples. Considering the IHC results, reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was performed to measure the expression level of 2 different exons of ERα, exon 6 and exon 7, which are part of the ligand binding domain of ERα, using the Taqman gene expression assay. Extra-nuclear expression of ERα using IHC demonstrated a statistically significant association with pathological invasiveness. RT-qPCR results exhibited a decreased expression of ERα exon 7 in invasive tumor tissues, compared with their adjacent normal tissues. This is consistent with the findings of previous in vitro studies indicating that extra-nuclear ERα were exon 7 splicing variants. No difference was observed in ERα exon 7 expression between normal and tumor tissues in non-invasive lung cancer tissues. When considering the EGFR mutation status, EGFR wild-type lung cancers exhibited decreased ERα exon 7 expression levels compared with EGFR mutated lung cancers. Extra-nuclear expression of ERα, which may represent exon 7 splicing variants of ERα, showed statistical association with pathological invasiveness in smoking-independent lung cancer. The post-translational splicing mechanism of ERα may be involved in the acquired invasiveness of smoking independent lung cancer.

Exon 7 splicing variant of estrogen receptor α is associated with pathological invasiveness in smoking-independent lung adenocarcinoma