Bronchioloalveolar invasion in non-small cell lung cancer is associated with expression of transforming growth factor-β1

BACKGROUND Adenocarcinoma in situ (AIS) and minimally invasive adenocarcinoma (MIA) with fibrous stromal invasion are newly introduced subtypes of small lung adenocarcinoma. AIS is a small localized adenocarcinoma in which growth is restricted to neoplastic cells along preexisting alveolar structures without fibrous stromal invasion. In MIA, by contrast, tumor cells have infiltrated the myofibroblastic stroma. Transforming growth factor (TGF)-β is known to be produced by progressor tumors, and excessive TGF-β contributes to a pathological excess of tissue fibrosis. TGF-β1 is the most abundant isoform, and its expression is a key event fostering tumor invasion and metastasis. We therefore analyzed the relationship between TGF-β1 expression and clinicopathological microinvasion in patients with small lung adenocarcinoma. METHODS The study participants were 45 patients who underwent curative surgery for AIS and MIA 3 cm or less in size. Those tumors were assessed based on immunohistochemical staining using anti-TGF-β1 antibody. The TGF-β1 status was assessed immunohistochemically using the Allred 8-unit system. RESULTS The rates of TGF-β1 positivity in the AIS and MIA groups were 27.3% and 65.2%, respectively (P <0.05). The median of Allred score was 0.5 (range 0-5) in the AIS group and 3.0 (range 0-6) in the MIA group (P = 0.0017). CONCLUSIONS We suggest that TGF-β1 expression is likely to be significantly stronger in patients with MIA than in those with AIS, and the increased expression may be associated with minimal invasion and infiltration of the myofibroblastic stroma.