Pouring petrol on the fire can potentially reverse resistance to hormone treatments for prostate cancer, new research suggests.
The counter-intuitive strategy called bipolar androgen therapy (BAT) involves boosting levels of the male hormone testosterone, which normally stimulates prostate cancer growth.
In a small pilot study, scientists found that alternating high and low testosterone levels caused seven of 16 patients with resistant prostate cancer to go into remission.
All 10 men who remained in the study until the end subsequently responded to a resumption of traditional hormone therapy.
The US scientists, led by Dr Michael Schweizer, from the University of Washington in Seattle, wrote in the journal Science Translational Medicine: "These data suggest that BAT may have the potential to reverse resistance to androgen-ablative therapies, potentially re-sensitising men to drugs to which their cancer had become resistant."
Men with prostate cancer that has spread are usually treated with anti-androgen treatments that either cut off their supply of testosterone or block its effect.
But most cancers stop responding to these treatments after one to three years. Patients are then said to be "castration-resistant", and may survive less than another two years.
The new work builds on previous research suggesting that tumour cells that have grown used to a low testosterone supply can be killed by unexpected high doses of the hormone.
Evidence suggests that a sudden surge of testosterone can inhibit the cancer cells' ability to replicate their DNA, and also triggers breaks in their DNA.
The men taking part in the pilot study all had castration resistant prostate cancer (CRPC) without experiencing any physical symptoms, such as pain.
All were given a treatment that switched between two extremes of high and low testosterone levels over a four week cycle.
Patients responded in one of three ways. Either their levels of the cancer blood marker PSA (prostate specific antigen) continued to go up, or they initially increased and then dropped, or they declined immediately by more than 50%.
Seven patients went into remission and experienced reductions in DNA. Imaging revealed that tumours shrank in four men, and completely disappeared in one.
After coming off the treatment, patients once again became sensitive to the hormone deprivation therapy that had previously failed them.
The scientists added: "Although this pilot study enrolled only a small number of patients, it provides compelling preliminary evidence that challenges the current treatment paradigm for CRPC."