Urology Medical News about Sunitinib malate, castration-resistant prostate cancer

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Sunitinib malate for metastatic castration-resistant prostate cancer following docetaxel-based chemotherapy
Annals of Oncology, 07/31/09

Sonpavde G et al. - In a study to evaluate sunitinib malate in pts with progressing metastatic castration–resistant prostate cancer (CRPC) following prior docetaxel, it was concluded that sunitinib malate demonstrated promising activity in metastatic CRPC progressing after prior docetaxel.

Methods

Pts with metastatic CRPC progressing following 1 to 2 chemotherapy regimens including docetaxel were included.
Primary endpoint was progression-free survival (PFS) per radiographic and clinical evaluations.
Oral sunitinib was administered 50 mg/day 4-wks on followed by 2-wks off per cycle up to a maximum of 8 cycles or until clinical progression or intolerable toxicity.

Results

36 pts with a median age of 69.5 yrs were accrued.
Median PFS was 19.4 wks with a 12-wk PFS of 75.8%.
4 pts (12.1%) had a 50% prostate-specific antigen (PSA) decline and 7 (21.2%) had a 30% PSA decline.
2 of 18 pts (11.1%) with measurable disease demonstrated 30% declines by RECIST and 8 (44.4%) displayed some shrinkage.
A decline in pain score of 2 points occurred in 13.6% of 22 assessable pts.
Drug discontinuation due to toxic effects occurred in 52.8% of pts.

Exclusive Author Commentary
Guru Sonpavde, MD, 08/01/09

This phase II trial was conducted by the US Oncology network in multiple community-based cancer centers and evaluated the safety and activity of single-agent sunitinib (without concurrent corticosteroids) in relatively heavily pretreated patients with metastatic CRPC (castration resistant prostate cancer) that had progressed following docetaxel. Additionally, 36.2% of patients had received one other chemotherapeutic agent and 11.1% had also received prior bevacizumab. With the caveat that this is a modest sized phase II trial, the relatively high composite 12-week PFS (progression free survival) of 75.8% (based on objective and symptomatic progression and not PSA progression) accompanied by 50% and 30% PSA declines in 12.1% and 21.2% of patients, respectively, support sunitinib being an active agent in this disease. These levels of PSA declines appear to be intermediate surrogates for long-term outcomes with chemotherapy. Although PFS is a soft end point in the setting of metastatic CRPC, it is a relevant end point that dictates clinical decisions. In addition, two of the four patients who had received prior bevacizumab displayed a 50% PSA decline and a 30% PSA decline, suggesting that these agents may not be completely cross-resistant. Although most toxic effects were mild, the majority of patients (52.8%) discontinued therapy due to toxic effects. As a result, the median TTF (time to treatment failure) was a more modest 11.8 weeks compared to the median PFS of 19.4 weeks. This elderly population of relatively heavily pretreated patients with metastatic CRPC may tolerate even mild toxic effects poorly compared with younger patients treated in other settings. Closer clinical monitoring and prompt dose reductions for early toxic effects may have mitigated these events. Therefore, the further development of sunitinib in this population warrants careful monitoring for toxic effects and optimal patient selection. Given the high rate of discontinuation of therapy due to toxic effects, a lower dose and less heavily pretreated population may be more optimal. Indeed, an ongoing phase III trial in the second-line setting is comparing sunitinib 37.5 mg daily continuously plus prednisone versus placebo plus prednisone.

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