Excellent prognosis of lepidic-predominant lung adenocarcinoma: low incidence of lymphatic vessel invasion as a key factor

To clarify the prognostic value of predominant histological subtypes for small-sized lung adenocarcinoma. Sixty-four specimens of resected invasive lung adenocarcinoma less than 20 mm in diameter with no lymph node metastasis were studied. These specimens were microscopically classified into predominant histological subtypes (21 lepidic, 16 acinar, 24 papillary, and three solid) according to the International association for the study of lung cancer/American thoracic society/European respiratory society adenocarcinoma classification. The relationships between tumor relapse and predominant histological subtypes were statistically analyzed. In addition the relationships between several pathological factors and predominant histological subtypes were statistically assessed. Kaplan-Meier relapse-free curves showed a five-year relapse-free rate of 100% in 64 patients with lepidic-predominant adenocarcinoma, compared with a rate of 73.7% (p=0.035 by log rank test) in patients with non-lepidic-predominant adenocarcinoma (papillary, acinar, and solid). The only statistically significant pathological factor between lepidic-predominant and non-lepidic-predominant histological subtypes was lymphatic vessel invasion as assessed by logistic regression analysis. In small-sized lung adenocarcinoma, lepidic-predominant histological subtype is the best prognostic factor, and a low incidence of lymphatic vessel invasion in the histological subtype is a key factor for an excellent prognosis.