Inclusion Criteria:

- Patients must have histologically confirmed malignancy that is metastatic or
unresectable and for which standard curative or palliative measures do not exist or
are no longer effective

- Tumor accessible to core needle biopsy and willingness to undergo this procedure
prior to the start of treatment

- Evaluable disease as defined in the RECIST criteria

- ECOG performance status =< 2

- Life expectancy of greater than 3 months

- Absolute neutrophil count > 1,500/ul

- Platelets > 100,000/ul

- Total bilirubin within normal institutional limits

- AST(SGOT)/ALT(SGPT) =< 2.5 X institutional upper limit of normal

- Creatinine < 2.0 mg/ml

- Ability to understand and the willingness to sign a written informed consent document

- Metastatic brain or meningeal tumors are allowed if the patient is > 1 month from
surgery and/or radiation and is clinically stable with respect to the tumor at the
time of the study entry and currently off corticosteroids

- Pregnancy test for pre-menopausal women

- The effects of PS-341 and topotecan on the developing human fetus are unknown; for
this reason women of childbearing potential and men must agree to use adequate
contraception (hormonal or barrier method of birth control) prior to study entry and
for the duration of study participation; should a woman become pregnant or suspect
she is pregnant while participating in this study, she should inform her treating
physician immediately

Exclusion Criteria:

- Creatinine clearance < 40 mL/min

- Patients who have had chemotherapy or radiotherapy within 4 weeks (6 weeks for
nitrosoureas or mitomycin C) prior to entering the study

- Those who have not recovered from adverse events due to agents administered more than
4 weeks earlier

- Patients may not be receiving any other investigational agents

- History of allergic reactions attributed to compounds of similar chemical or biologic
composition to topotecan, PS-341 or other agents used in this study

- Uncontrolled intercurrent illness including, but not limited to, ongoing or active
infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac
arrhythmia, or psychiatric illness/social situations that would limit compliance with
study requirements

- Pregnant women are excluded from this study because topotecan is an agent with the
potential for teratogenic or abortifacient effects; because there is an unknown but
potential risk for adverse events in nursing infants secondary to treatment of the
mother with topotecan and PS-341, breastfeeding should be discontinued; these
potential risks may also apply to other agents used in this study

- Because patients with immune deficiency are at increased risk of lethal infections
when treated with marrow-suppressive therapy, HIV-positive patients receiving
combination anti-retroviral therapy are excluded from the study because of possible
pharmacokinetic interactions with topotecan and PS-341 or other agents administered
during the study.; appropriate studies will be undertaken for patients receiving
combination anti-retroviral therapy when indicated