A landmark randomized trial has identified the first predictive biomarker for hormone therapy in recurrent prostate cancer, offering clinicians a powerful tool to personalize treatment decisions for patients experiencing disease recurrence after surgery. The phase II BALANCE trial (NRG Oncology GU006) demonstrated that the PAM50 gene expression test can accurately identify which patients will benefit from adding hormone therapy to radiation treatment.
The study, led by Dr. Daniel Spratt from University Hospitals Seidman Cancer Center and Case Western Reserve University School of Medicine, addresses a decades-old clinical challenge in prostate cancer management. "We've been searching for decades for a way to determine which patients are most likely to respond to hormone therapy after prostatectomy," said Dr. Spratt, the trial's principal investigator. "We now have a tool that lets us tailor treatment based on a tumor's biology and recommend hormone therapy only for those patients who we think can expect to see a benefit."
Clinical Context and Unmet Need
Prostate cancer ranks as the second most common cancer worldwide, with more than 314,000 new diagnoses expected in the U.S. this year. While patients with localized disease have effective treatment options including radical prostatectomy or definitive radiation therapy, up to 30% experience disease recurrence, typically detected through rising prostate-specific antigen (PSA) levels.
For patients with biochemical recurrence after surgery, radiation therapy serves as the standard treatment and has been shown to improve survival. Hormone therapy is commonly added to radiation to block or reduce testosterone, which fuels prostate cancer growth. However, this approach carries significant side effects including fatigue, bone loss, hot flashes, metabolic changes, and cardiovascular risk.
"Testosterone is important for maintaining bone, muscle, cognitive and cardiac health, but it's also the key fuel driving prostate tumors," explained Dr. Spratt. "Until now, we haven't had a reliable way to tell who really needs hormone therapy and who does not."
PAM50 Biomarker Technology
The breakthrough came through adapting PAM50, a gene expression test originally developed for breast cancer treatment, to capture prostate cancer biology. Developed by Dr. Spratt and colleagues Felix Feng, MD, FASTRO, and Shuang Zhao, MD, the adapted test classifies prostate tumors into molecular subtypes based on their genetic characteristics.
Similar to breast cancer classification, prostate tumors can be grouped as either luminal B or non-luminal B subtypes. Luminal B tumors grow more quickly and demonstrate high responsiveness to hormone therapy, while non-luminal B tumors, including luminal A and basal-like subtypes, are generally less dependent on testosterone and may not respond to hormone-based treatment. Dr. Spratt compared this advance to breast cancer, where estrogen receptor status guides endocrine therapy decisions.
BALANCE Trial Design and Results
The BALANCE trial enrolled 295 patients with recurrent prostate cancer and no signs of metastasis across cancer centers throughout the U.S. All participants had undergone prostatectomy and were experiencing rising PSA levels, with 86% having entry PSA levels below 0.5 ng/mL. Patients were randomized to receive standard radiation therapy combined with either six months of apalutamide, a second-generation anti-androgen therapy, or placebo.
Tumor specimens were tested using PAM50 and classified as luminal B (n=127) or non-luminal B (n=168). The primary endpoint was biochemical progression-free survival, measuring cancer recurrence based on PSA levels, disease progression, metastasis, or death over a median follow-up of five years.
Biochemical Progression-Free Survival
The results revealed a striking difference in treatment response based on tumor subtype. Patients with luminal B tumors experienced significant benefit from hormone therapy, achieving 72.4% five-year biochemical progression-free survival with apalutamide compared to 53.9% with placebo (p=0.0062).
In stark contrast, patients with non-luminal B tumors saw no improvement from hormone therapy, with nearly identical five-year biochemical control rates between treatment arms: 70.2% with apalutamide versus 71.1% with placebo (p=0.44).
Metastasis-Free Survival
A similar pattern emerged for metastasis-free survival, a critical indicator of disease control. Among luminal B patients, five-year survival without metastasis reached 94.7% with hormone therapy compared to 81.8% with placebo (p=0.029). The non-luminal B group showed no difference, with 89.9% versus 89.3% metastasis-free survival rates (p=0.90).
"The patients with luminal B tumors saw a large benefit, both in reducing recurrence and lowering the risk of metastatic disease," said Dr. Spratt. "But for patients without this subtype, hormone therapy didn't change the outcome. That's incredibly valuable information when we're trying to personalize care."
Clinical Implications and Future Implementation
Dr. Spratt believes these findings will be practice-changing, representing the first prospectively validated predictive biomarker in prostate cancer. "It gives us a promising way to personalize care, recommending hormone therapy for those who respond, and avoiding unnecessary treatment when it is unlikely to help," he stated.
The definitive nature of the results suggests that further phase III confirmatory studies may be unnecessary. "The magnitude of benefit - and the complete lack of benefit in some patients - makes it unlikely that we could ethically enroll patients in a follow-up trial," Dr. Spratt explained. "PAM50 could now be used in recurrent prostate cancer to support shared decision-making."
This biomarker-driven approach could revolutionize treatment personalization by identifying the subset of patients who truly benefit from hormone therapy while sparing others from unnecessary toxicity. The paradigm shift promises to streamline clinical decision-making, optimize patient quality of life, and reduce healthcare costs associated with overtreatment.
The integration of PAM50 testing into clinical practice represents a significant advance toward precision medicine in prostate cancer, setting a precedent for genomic-guided treatment decisions beyond the post-prostatectomy setting. As clinical guidelines evolve to incorporate these findings, PAM50 testing is expected to become a standard component of recurrent prostate cancer management, bringing personalized oncology closer to reality for patients worldwide.
