Patients whose prostate cancer is being regularly monitored rather than actively treated may be at higher risk for progression to a more aggressive malignancy if their testosterone levels are low, according to a new study.

The finding suggests that testosterone may serve as a useful risk marker and help doctors tailor monitoring strategies for patients choosing active surveillance, according to a report of the study published in The Journal of Urology.

“Active surveillance is a safe and effective option for many men with early-stage prostate cancer. However, identifying which patients may be more likely to experience progression remains a key challenge,” study leader Dr. Justin Gregg of The University of Texas MD Anderson Cancer Center said in a statement.

Reviewing medical records from more than 900 men who opted for surveillance, his team found that testosterone levels of 300 nanograms per deciliter or lower at the start were linked with an increase in the likelihood of disease progression to Grade 3, the most aggressive form.

This was the case even after accounting for other factors including age, prostate-specific antigen level, body mass index, and tumor density and size.

A low testosterone level was not associated with progression to Grade 2 disease, the researchers also found.

The study does not suggest that low testosterone causes aggressive cancer but rather that the association could help guide monitoring and decision-making, the researchers said.

“Understanding how hormonal factors influence prostate cancer biology may help us refine surveillance strategies,” Gregg said.