Expression of alpha-smooth muscle actin in small bronchioloalveolar adenocarcinoma of the lung: Assessment and comparison with Noguchi criteria

The Noguchi criteria are useful in assessing the prognosis of patients with small lung adenocarcinoma. Although there is a significant difference in p rognosis between type A or B and type C, it is difficult in some cases to d istinguish these types accurately by microscopy. In this study, we used imm unohistochemistry to examine alpha-smooth muscle actin (alpha-SMA) produced by active fibroblasts in 25 pulmonary adenocarcinomas less than 2 cm in di ameter. Eleven of type C (61%) showed positive staining for alpha-SMA, wher eas no positive cases were seen in type A or B. The incidence of cancerous blood vessel and lymphatic invasion were significantly higher in alpha-SMA positive cases than in negative cases, and the positive cases showed poorer prognosis. These findings indicate that immunohistochemical detection of a lpha-SMA is useful and essential for histological typing by the Noguchi cri teria.