99mTc-anti-CEA radioimmunoscintigraphy of lung adenocarcinoma. Anti-carcinoembryonic antigen radioimmunoscintigraphy (anti-CEA RIS) in colorectal adenocarcinoma has been reported to allow a better estimation of the local tumor extension than other radiologic methods. This study evaluated the clinical feasibility of a 99mTc-labeled anti-CEA monoclonal antibody (BW 431/26, Behring Institute, FRG) in 11 patients for staging of primary adenocarcinoma of the lung. The primary tumor size ranged from 3 to 8 cm with a mean of 4 cm. Mediastinal and hilar nodes were present in four patients, intrapulmonary metastases were present in two patients, and pleural and liver metastases were present in one patient each. The CEA levels were in the range of 2 to 265 ng/ml and elevated (greater than 5 ng/ml) in six patients. Planar scintigraphy was performed at 6 h and 24 h post injection (pi). Analog and digitized images were interpreted by two observers. One patient was imaged twice and experienced serum sickness due to human anti-mouse antibodies (HAMA) after the second study, which showed marked unspecific tracer uptake in liver, spleen, and bone marrow, but no specific uptake by the tumor and was excluded from further analysis. Visual interpretation identified the primary tumor clearly in seven patients. No tumor imaging was observed in two patients. Two patients were classified as having questionable imaging due to a poor separation of tumor uptake from mediastinal blood pool. The primary tumor could be clearly delineated in both patients after comparison with the chest radiograph. Thus, the overall sensitivity for imaging of the primary tumor was 82 percent. The average target/background ratio was 1.31 +/- 0.17:1 at 6 h pi, and 1.30 +/- 0.16:1 at 24 h pi. Hilar and mediastinal nodes were correctly suspected in three patients, but the cardiac blood pool hampered a clear interpretation. Intrapulmonary and pleural metastases were diagnosed in all cases. The single liver metastasis was missed because of the high unspecific tracer uptake. Planar anti-CEA RIS with 99mTc BW 431/26 was superior to computed tomography (CT) in one case with subtotal tumor resection. We summarize that at present, planar anti-CEA RIS with 99mTc BW 431/26 cannot be advised as a routine staging procedure in adenocarcinoma of the lung, but it may be helpful in the detection of residual or recurrent tumor tissue. 