Some caveats
As only about a fifth of patients experienced PFS2 events, “these findings need to be interpreted with some caution,” said invited discussant Dana E. Rathkopf, MD, a genitourinary medical oncologist at Memorial Sloan Kettering Cancer Center in New York.
Dr. Dana E. Rathkopf
Another caveat is that the cohort analyzed comprised poor responders, who had experienced progression at a median of roughly 12 months whether on apalutamide or placebo, she noted. “If the patients were all on treatment for about 12 months, it does make me wonder why the apalutamide patients responded better than placebo patients to a second hormonal therapy, because you might think that, in the setting of poor response to upfront apalutamide, these patients may develop some type of intrinsic resistance that would suggest they would not respond to a second-line androgen receptor inhibitor relative to a taxane.”
Patients in TITAN were stratified on prior receipt of docetaxel before undergoing randomization. But simply by chance, among those receiving subsequent hormonal therapy, a larger share of those initially treated with apalutamide than of those initially treated with placebo had received the taxane (33% vs. 16%), which may have influenced outcomes, Dr. Rathkopf added.
“Further maturation of the data will tell us more,” she said. “But clearly, apalutamide in both the SPARTAN and TITAN trials improved PFS2 relative to placebo, and this begs the question of how we can better select treatment using predictive markers.”