Background: There are no standard treatments for men who have demonstrated a good response to TAX without signs of progression. The mTOR pathway is involved in many aspects of CRPC, and mTOR inhibitors have shown significant anti-CRPC activity in preclinical testing. Therefore, we designed a phase II trial to explore whether maintenance therapy with TEM has the potential to prolong response to TAX without compromising quality of life. Methods: For this single-arm, multicenter phase II trial we recruited CRPC pts with documented treatment response by PSA (> 50% decline from baseline) or RECIST (1.0) criteria following ≥ 6 to 10 cycles of TAX (75 mg/m² q3wks). Subjects received weekly TEM (25 mg iv x 4/cycle). The primary endpoint was time to treatment failure (TTF; RECIST or symptomatic progression). Secondary endpoints included safety (NCI-CTCAE v3.0), quality of life (FACT-P, PPI), changes in PSA, objective tumor response rate, and overall survival. We were also studying surrogate markers of TEM activity, including the enumeration of circulating endothelial cells (CEC) as a potential indicator of the antiangiogenic effects of TEM. Results: 19 pts have been enrolled to data after a median of 7 cycles of TAX. The mean age was 68 years (range 51-82), and the median baseline PSA 17.3 (0.02-380.7). 15 pts had received prior local radiation therapy, 6 surgery. 17 pts had bone metastases, 9 visceral and 8 nodal disease. Pts received a median of 4 cycles of TEM (maximum 23 and continuing), resulting in a median TTF of 5.8 (95%CI 3.8-9.2) months. No PSA responses were seen (time to PSA progression 1.8 months), but 1 PR. 8 pts achieved SD. 12 pts have been discontinued due to treatment failure (RECIST [4], symptomatic [7], combined [1]), and 3 for other reasons, including TEM-associated toxicity (lymphedema [1]). TEM has been generally well tolerated without unexpected adverse events or negative impact on quality of life. The median overall survival has not yet been reached. There is a trend for TEM to reduce viable CEC amid large inter/intrapatient CEC variability. Conclusions: TEM maintenance therapy in CRPC pts that have responded to TAX appears to be well tolerated and results in meaningful prolonged TTF.