Circulating tumor cell count predicts prostate cancer survival, can help tailor treatment
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Key takeaways:
- Men with five or more circulating tumor cells/7.5 mL at baseline had a more than threefold risk for death compared with men with no circulating tumor cells.
- Men with five or more cells had the shortest survival.
A blood test for men at the time of a metastatic prostate cancer diagnosis may predict treatment response and survival, according to study results.
The test could help oncologists decide which patients should receive standard treatment and who might derive more benefit from a clinical trial, researchers concluded.
“Prostate cancer is the most common malignancy [among] American men and the second most lethal,” Amir Goldkorn, MD, professor of medicine and biochemistry & molecular medicine at Keck School of Medicine and associate director for translational research at USC Norris Comprehensive Cancer Center, told Healio. “New drugs are emerging, but there are very few assays that can tell physicians how well a given patient will fare over time and with treatment.
“This study aimed to address that need by testing whether circulating tumor cell count could serve as a noninvasive blood test predictive of OS right at the start of hormonal therapy for metastatic prostate cancer,” Goldkorn added. “Most men are on first-line hormonal therapy for years, then treated with a variety of other drugs (eg, chemotherapy), so we were surprised that circulating tumor cell count right at the start of their treatment was still so predictive of their overall survival, regardless of all subsequent therapies over time.”
The analysis included 1,313 men (median age, 68 years; interquartile range, 44-92) with metastatic hormone-sensitive prostate cancer who participated in the randomized phase 3 S1216 study.
Researchers obtained peripheral blood samples at time of trial registration for a baseline reading, and they did so again at the time of progression to metastatic castration-resistant prostate cancer. They categorized counts as 0, one to four, or five or more circulating tumor cells per 7.5 mL.
Investigators assessed associations between circulating tumor cell counts and three outcomes — OS, PFS and 7-month PSA.
Researchers collected 503 evaluable samples from men (median age, 69 years) with newly diagnosed metastatic hormone-sensitive prostate cancer at baseline, and they collected 93 samples at time of progression.
They determined 60 samples (11.9%) had five or more circulating tumor cells per 7.5 mL, 107 samples (21.3%) had one to four circulating tumor cells, and 336 samples (66.8%) had no circulating tumor cells.
Men with no circulating tumor cells achieved significantly longer median OS (not reached) than those who had one to four circulating tumor cells (56.2 months; 95% CI, 45.7-69.8) and those who had five or more (27.9 months; 95% CI, 24.1-31.2).
After adjusting for clinical covariates at baseline, men with five or more circulating tumor cells had a significantly higher risk for death (HR = 3.22; 95% CI, 2.22-4.68) and disease progression (HR = 2.46; 95% CI, 1.76-3.43), as well as a lower likelihood of PSA complete response (OR = 0.26; 95% CI, 0.12-0.54), than men with no circulating tumor cells.
Researchers acknowledged study limitations, including their inability to analyze baseline circulating tumor cell counts for all men who participated in the S1216 trial — given circulating tumor cell collection had been added by protocol amendment as a correlative endpoint after study accrual started — as well as absence of data about whether men had undergone prostatectomy.
“Based on this study, baseline [circulating tumor cell] count could be used as a baseline biomarker to identify men with poor prognosis for enrollment in clinical trials of new, more aggressive treatment regimens,” Goldkorn told Healio. “Building on our findings, [it] can potentially be used to identify patients for new clinical trials.
“We are also currently conducting other NIH-sponsored studies combining [circulating tumor cell] count with other liquid biopsy assays like DNA sequencing of [circulating tumor cells] and circulating tumor DNA,” he added. “We hope these will yield even more informative biomarkers to guide management of our patients.”
For more information:
Amir Goldkorn, MD, can be reached at agoldkor@med.usc.edu.
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