) SCLC constitutes a major and persistent public health problem in the US. It comprises 20-25 percent of the 178,100 lung cancers estimated in 1997. Despite progress towards smoking cessation, the benefits with respect to this and other forms of lung cancer may not accrue for another ten years or more. Hence, SCLC will remain a major cancer problem. Approximately two thirds of SCLC cases present as extensive disease (ED), with thoracic spread beyond practicable radiation ports or extra-thoracic metastasis. Despite the inherent chemo- and radiosensitivity of this histologic type of lung cancer, long-term survival (i.e., beyond 5 years) is very rare (1-2 percent) and median survival durations are less than 1 year in most studies. We wish, therefore, to test the hypothesis that high dose RAIT can be safely applied to patients with ED-SCLC, who have persistent, measurable disease after first-line chemotherapy. ED-SCLC is well suited to the clinical application of this promising, orthogonal therapeutic modality, given its dismal long-term survival prospects and its inherent radiosensitivity. We will conduct a phase I dose escalation trial for patients with ED- SCLC, who have completed first-line chemotherapy and who have persistent, measurable disease using a radiolabeled form of the humanized anti-CEA monoclonal antibody (mAb), hMN-14. Due to the availability of a stable chelating agent, the radionuclide, 90Y, will be used for therapy. For imaging, documentation of tumor targeting and determination of the radiation absorbed doses to normal organs and tumor sites, the 111In isotope will be used, which is known to closely approximate the pharmacokinetics and biodistribution of the 90Y-hMN-14 mAb. Peripheral blood stem cells will be utilized to allow for dose escalation and for determination of the dose-limiting toxicities, maximum tolerated dose and overall safety of this novel, high dose RAIT approach.