Expression of blood-group antigen A--a favorable prognostic factor in non-small-cell lung cancer. BACKGROUND. New prognostic factors are needed to guide the treatment of patients with non-small-cell lung cancer. We evaluated the prognostic value of altered expression of ABH blood-group antigens, which has been implicated in the multistep process of carcinogenesis and tumor progression. METHODS. The presence of blood-group antigens was assessed immunohistochemically in paraffin-embedded tumor samples from 164 patients who underwent curative surgery for non-small-cell lung cancer from 1980 through 1982. Monoclonal antibodies were used to detect the A and B antigens, and Ulex europaeus agglutinin I to detect H antigen. RESULTS. Survival of the 28 patients with blood type A or AB who had primary tumors negative for blood-group antigen A was significantly shorter than that of the 43 patients with antigen A-positive tumors (P less than 0.001) and of the 93 patients with blood type B or O (P = 0.002). The respective median survival times were 15, 71, and 39 months. Disease progressed significantly earlier in the 28 patients with tumors negative for blood-group antigen A than in the antigen A-positive patients (P less than 0.001). Expression of blood-group antigen B or H in tumor cells did not correlate with survival. Cox proportional-hazards regression analysis showed that expression of blood-group antigen A in tumor cells added significantly to the prediction of overall survival provided by other known prognostic factors among the patients with blood type A or AB (P = 0.004). CONCLUSIONS. Expression of blood-group antigen A in tumor cells is an important favorable prognostic factor in patients with non-small-cell lung cancer. This variable needs to be considered in the design of future trials of therapy. 