Study of 89Zr-DFO-MSTP2109A in Patients With Prostate Cancer

Inclusion Criteria:

- To be included in this study, patients should be eligible for enrollment into protocol
11-016 (therapy with the DSTP3086S ADC) or meet all of the following criteria:

- Patients meeting the criteria for enrollment on research protocol 11-016 to receive
DSTP3086S ADC (therapeutic ADC based on MSTP2109A) will be the preferred patients for
this study. Patients that are to receive DSTP3086S will not be injected with DSTP2086S
until imaging with 89Zr-DFOMSTP2109A is finished, approximately 1 week.

- Adult male > 21years of age

- Visible lesions by either CT, bone scan or MRI consistent with metastatic disease

- Metastatic progressive disease

- Imaging modalities:

- Bone scan: new osseous lesion and/or MRI or CT: An increase in measurable soft tissue
disease or the appearance of new sites of disease.

Or

- PSA changes over range of value 26%

- Patients with histologically confirmed prostate cancer at MSKCC

- STEAP1 antigen positive tissue known from prior IHC testing or if STEAP1 status is not
known archival sample will be sent to Genentech for IHC. Samples need to be positive,
when feasible metastatic lesions will be tested preferentially rather than the
primary.

- Performance status of 60 or higher (Karnofsky scale) (Appendix A)

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

- PSA levels to be taken within 2 weeks of antibody administration.

Exclusion Criteria:

- Patients meeting any of the following exclusion criteria will not be eligible for
study entry:

- Previous anaphylactic reaction to human, humanized or chimeric antibody

- Hematologic

- Platelets <75K/mcL

- ANC <1.0 K/mcL

- Hepatic laboratory values

- AST/ALT >2.5 x ULN

- Renal laboratory values

- Bilirubin >1.5 x ULN (institutional upper limits of normal)

- eGFR < 30mL/min/1.73m2

- Patients with history of hypersensitivity reaction to any component of
89Zr-DFOMSTP2109A, including DFO