Randomized phase II trial of sipuleucel-T immunotherapy preceded by sensitizing radiation therapy and sipuleucel-t alone in patients with metastatic castrate resistant prostate cancer.

222Background: Sipuleucel-T (sip-T) is an autologous cellular vaccine indicated for patients (pts) with asymptomatic or minimally symptomatic metastatic castration resistant prostate cancer (mCRPC). Since radiation therapy (RT) can suppress the bone marrow function and immune response, previous studies evaluating sip-T excluded pts who received RT less than or equal to 28 days prior to sip-T therapy. Recent evidence suggests that RT may act synergistically with immunotherapy to enhance and broaden antitumor immune response. Methods: Pts who met standard criteria for sip-T were randomized to receive sip-T alone (Arm A) or sip-T initiated 1 week after completing sensitizing RT to single metastatic site (Arm B). RT was delivered at 300cGy/day to 3000 cGy total. The primary endpoint was the ability to safely combine sip-T preceded by RT and generate sip-T product with adequate immune activation parameters. Secondary endpoints included the measurement of immune responses to prostatic acid phosphatase (PAP) and...