The male hormone testosterone, believed to be a feeder of prostate cancer, can actually help suppress some advanced prostate cancers, a surprising new study has found.
Testosterone therapy may also reverse resistance to testosterone-blocking drugs used to treat prostate cancer, researchers said.
Medical oncologist Samuel Denmeade at the Johns Hopkins Kimmel Cancer Center who led the study cautioned that the timing of testosterone treatment used in his research is critical and difficult to determine, and said men should not try to self-medicate their cancers with testosterone supplements available over the counter.
In men whose prostate cancer spreads, doctors typically prescribe drugs that block testosterone production, but cancer cells eventually become resistant to this means of reducing the hormone, said Denmeade, a professor of oncology at the Johns Hopkins University School of Medicine.
At that point, physicians switch to other drugs, such as enzalutamide, which block testosterone's ability to bind to receptors within prostate cancer cells.
Denmeade said the combination of drugs that block testosterone production and receptors, called androgen deprivation therapy, may make prostate cancer more aggressive over time by enabling prostate cancer cells to subvert attempts to block testosterone receptors.
The new study tested an approach based on the idea that if prostate cancer cells were flooded with testosterone, the cells might be killed by the hormone shock.
Denmeade and his colleagues enrolled 16 men who had been receiving testosterone-lowering treatment for metastatic prostate cancer at Johns Hopkins.
All had been treated previously with at least one type of androgen deprivation therapy and had rising levels of prostate specific antigen (PSA), a blood marker for prostate cancer, and radiographic evidence their cancers were becoming resistant.
The men were given three 28-day cycles of an intramuscular injection of testosterone and two weeks of a chemotherapy drug called etoposide.
Men who showed decreases in PSA levels after three cycles were continued on testosterone injections alone.
Of the 16, two did not complete the study. Of the 14 remaining in the trial, seven experienced a dip in their PSA levels of between 30 and 99 per cent, an indication their cancers were stable or lessening in severity. Seven of the men showed no decrease in PSA, 'news-medical.Net' reported.
In addition, four of the seven men stayed on testosterone therapy for 12 to 24 months with continued low PSA levels. Of 10 men whose metastatic cancers could be measured with imaging scans, five experienced tumour shrinkage by more than half, including one man whose cancer completely disappeared.
The scientists said these results suggest that testosterone therapy has the potential to reverse the resistance that eventually develops to testosterone-blocking drugs like enzalutamide.
