Clinical and correlative results of SWOG S0354: a phase II trial of CNTO328 (siltuximab), a monoclonal antibody against interleukin-6, in chemotherapy-pretreated patients with castration-resistant prostate cancer.
OBJECTIVE
Interleukin-6 (IL-6) facilitates cancer cell survival via pleotrophic effects. We conducted a multicenter phase II study of CNTO328 (siltuximab) as second-line therapy for men with castration-resistant prostate cancer.


METHODS
Eligible men had castration-resistant prostate cancer treated with one prior chemotherapy. Subjects were treated with 6 mg/kg CNTO328 i.v. every 2 weeks for 12 cycles. Response was assessed after every three cycles. Primary end point was prostate-specific antigen (PSA) response rate defined as a 50% reduction. Accrual was planned in two stages, with 20 eligible patients in the first stage and 40 overall. Plasma cytokines and growth factors were measured by Luminex.


RESULTS
Fifty-three eligible subjects had all received prior taxane therapy. Two (3.8%; 95% CI, 0.5-13.0%) had PSA response. None of the 31 patients with measurable disease had a RECIST (Response Evaluation Criteria in Solid Tumors) response but 7 (23%) had stable disease. With median follow-up of 14.8 months, median progression-free survival was 1.6 months (95% CI, 1.6-1.7) and median overall survival was 11.6 months (95% CI, 7.5-19.0). Grade 3/4 toxicities included disseminated intravascular coagulation (1), central nervous system ischemia (1), elevated aspartate aminotransferase (1), gastritis/esophagitis (2), thrombocytopenia (2), pain (2), leukopenia (1), and neuropathy (2). Median baseline IL-6 levels were 12.5 pg/mL (interquartile range, 2.5-41.5). Patients with IL-6 >12.5 pg/mL had worse survival than those with levels <12.5 pg/mL (53% versus 94%; P = 0.02). After treatment, IL-6 levels were >250-fold higher. Thirty-two of 38 patients had a decline in C-reactive protein plasma levels at 6 weeks.


CONCLUSIONS
CNTO328 resulted in a PSA response rate of 3.8% and a RECIST stable disease rate of 23%. Declining C-reactive protein levels during treatment may reflect biological activity. Despite evidence of CNTO-mediated IL-6 inhibition, elevated baseline IL-6 levels portended a poor prognosis.
Dorff
Tanya B
TB
University of Southern California, Norris Comprehensive Cancer Center, Los Angeles, California 90033, USA. dorff@usc.edu
Goldman
Bryan
B
Pinski
Jacek K
JK
Mack
Philip C
PC
Lara
Primo N
PN
Van Veldhuizen
Peter J
PJ
Quinn
David I
DI
Vogelzang
Nicholas J
NJ
Thompson
Ian M
IM
Hussain
Maha H A
MH
D000368:Aged; D000369:Aged, 80 and over; D000911:Antibodies, Monoclonal / Q000009:adverse effects / Q000627:therapeutic use*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use; D002369:Castration; D019008:Drug Resistance, Neoplasm; D006801:Humans; D008297:Male; D008875:Middle Aged; D011471:Prostatic Neoplasms / Q000188:drug therapy* / Q000401:mortality; D019233:Retreatment; D000093242:Interleukin-6 Inhibitors
D000911:Antibodies, Monoclonal; D000093242:Interleukin-6 Inhibitors; C504234:siltuximab