Inclusion Criteria

Inclusion:

- Histologically or Cytologically proven SCLC, CD 56+ small cell carcinoma of unknown
origin, or CD56+ non-pulmonary small cell carcinoma

- Relapsed disease; defined as patients with an initial response (partial or complete)
to first-line therapy, then relapse more than 3 months after completion of last
chemotherapy.

- Patients must have received no more than 3 prior chemotherapy regimen.

- Patients must have measurable disease defined as: Lesions that can be measured in at
least one dimension according to RECIST

- Predicted survival of 3 months or more

- Zubrod performance status 0-2

- Patients must not have received chemotherapy or radiation therapy within 4 weeks of
study entry, nor have planned surgery.

- Absolute neutrophils greater than or equal to 1.5 x 10^9/l, hemoglobin greater than
or equal to 9g/dl and platelets greater than or equal to 100 x 10^9/l.

- Creatinine less than or equal to 1.5 times the upper limit of normal

- AST/ALT less than or equal to 3 times the upper limit of normal without liver
metastases; less than or equal to 5 times the upper limit of normal with liver
metastases and bilirubin less than or equal to 1.5 times the upper limit of normal.

- Patients must have normal thyroid function (patients receiving thyroxin replacement
therapy who are biochemically euthyroid may be enrolled).

- Women of childbearing potential must provide a negative pregnancy test at screening
and use adequate contraception in the opinion of the investigator, for the duration
of study.

- Patients must be capable of understanding the nature of the trial and must give
written witnessed informed consent prior to any screening procedure.

Exclusion:

- Significant residual neurological or cardiac toxicity (grade 3 or 4) following
previous chemotherapy

- Patients who are concurrently receiving other anti-neoplastic treatment
(chemotherapy, radiotherapy, or immunotherapy including steroid therapy).

- Myocardial infarction within 6 months of study entry, unstable angina pectoris,
uncontrolled congestive heart failure, uncontrolled arrythmia, severe aortic
stenosis, a history of multiple sclerosis, or other demyelinating disease,
Eaton-Lambert Syndrome, history of hemorrhagic stroke, any CNS injury with residual
neurologic deficit, ischaemic stroke within the last 6 months, current known herpes
zoster (shingles), or cytomegalovirus infection, or a history of recurrent infections
with these viruses, chronic alcoholism, serious concomitant infection, or any other
concomitant illness considered significant enough to interfere with the study
outcome.

- Other investigational agents must not be taken during the study or within 4 weeks of
study entry.

- Previous monoclonal antibody therapy

- Patients must not have known central nervous system metastases

- Previous malignancy with < 5 year disease free interval from the last therapeutic
intervention, except for adequately treated basal cell carcinoma of the skin or
carcinoma in situ of the cervix.

- Patient unwilling or unable to tolerate and comply with the requirements of the
study.

- Pregnant or lactating females.