NEW YORKA small trial of trastuzumab(Drug information on trastuzumab) (Herceptin) alone and with paclitaxel(Drug information on paclitaxel) (Taxol) found that the combination was active against prostate cancer, but trastuzumab alone was not. The results were presented at the ASCO meeting by Michael J. Morris, MD, of Memorial Sloan-Kettering Cancer Center.
The study included 23 prostate cancer patients (median age, 66) stratified according to whether they were androgen dependent or independent and whether their degree of HER2 expression was 2+ or larger or less than 2+, as determined by immunohistochemistry using a DAKO kit.
While trastuzumab has been shown to improve survival in patients with HER2+ breast cancer, its effect on prostate cancer and the impact of the degree of tumoral HER2 expression on Herceptin efficacy are unknown, Dr. Morris said.
All patients received trastuzumab at doses of 2 mg/kg/week (IV over 30 minutes with a first-week loading dose of 4 mg/kg).
After assessment at 12 weeks, those with stable disease were to continue with trastuzumab alone, and those with disease progression were to cross over to trastuzumab with paclitaxel, administered at 100 mg/m² for 12 weeks, for a maximum of three cycles. At 12 weeks, however, all patients had progressed, so none continued on trastuzumab alone.
Stable Disease or Better
Evaluation of the trastuzumab/paclitaxel combination showed that in the androgen-independent group, two of four patients who were HER2 positive and four of nine who were HER2 negative had stable disease or better, while the others progressed.
In the androgen-dependent group, the two evaluable patients who were HER2 negative had stable disease or better.
Dr. Morris concluded, Our preliminary data suggest that Herceptin alone has a limited role for the treatment of androgen-independent HER2-negative tumors.
ASCO discussant Philip Kantoff, MD, of Dana-Farber Cancer Center, noted that HER2 overexpression appears to be unusual in primary prostate cancer, but may be more common in metastatic disease.
Regarding the responses to the trastuzumab/paclitaxel combination in this small study, he stated, Of course, the contribution of Herceptin to these responses is uncertain.