Thursday, February 19, 2009

Prostascint Scans

MP presents on the utility (or lack thereof) of Prostascint

Prostascint is based off of a PSMA (prostate specific membrane antigen) antibody - capromab.  FDA approved in 1996 for diagnosis and staging in high risk disease and for PSA recurrence after RP.

The scan is performed by In-111 conjugated capromab.  Scan is performed with Tc99m to differentiate pathologic uptake from vasculature.  Recently these have been fused with CT or MRI.  Cost per scan is ~2,000$

Pt presented with intermediate risk disease (GS 3+4 with organ confined disease treated with prostatectomy, with persistent PSA of 0.3ng/ml postoperatively).  A prostascint is obtained and reveals paraaortic uptake without CT correlate, and no activity in the prostate bed.

Test Characteristics.
Sensitivity - true positives/true positives + false negatives
Specificity - true negatives/true negatives + false positives

Elgamal - 100pts with 136 scans.  124 has positives prostascints - all positives were biopsied, and some of the negatives (though this was not well controlled)
Sensitivity - 89%
Specificity - 67%
Bone scan didn't correlate well the Prostascint (sensitivity of prostascint was only 57% for bone scan positive disease)

Multiple studies exist demonstrating a wide range of sensitivity of 36-86%

Raj Cancer 2002 - 222 pts with early biochemical failure after surgery.  174 scans were positive.  False negative rate was 31% in this cohort.  Sensitivity of a subset was 73% and specificity of 53%, PPV 89% - however they utilized response to RT and later progression as the gold standard.

Kahn JCO 1998 - 32pt treated with 60GY postoperatively.  5 negative scans, 18 has bed only, 9 had distant disease.  Prostascint didn't dictate therapy in this case.  Durable clinical response (DCR) was rare in those with distant uptake (27%).  In those with prostate bed uptake DCR had a 62% DCR rate and 88% in those with no uptake.  Some were biopsied in the bed - sensitivity was 78%, specificity 7%.

Proano J Urol 2006 - 44 pts with biochemical recurrence after RP - salvage RT used in all, nodal basins were radiated when Prostascint positive in nodal basins.  41% with a positive scan progressed vs 10% with a negative scan.  Data presented however without KM(Kaplan Meier) estimates.

Nagda IJROBP 2007 - 58 pt with prostascint scan after biochemical recurrence after RP.  Salvage RT used in all.  No difference in any of the prosascint results (distant uptake, bed uptake, or no uptake).  KM estimates used.  Sensitivity 30%, Specificity 58% (using recurrence as the gold standard for presence of disease)

Thomas JCO 2003 - 30 pts with biochemical recurrence after RP.  Prostascint positivity not predicitive of biochemical recurrence.

Koontz IJROBP 2008 - pooled data from some of the above trials - no difference in outcomes dependent on prostascint.

Case outcome - Prostascint results were not utilized in determining treatment - Salvage RT was delivered to 66Gy.  Pt also seen by medical oncology - they agreed with the assessment.  Pt had a complete biochemical response to RT.  Note: patient was treated where scan was negative, and not treated where positive, and a biochemical response was seen.

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