Delaying surgery on small, low-grade prostate tumours does not increase the risk of the disease progressing to an incurable form, research suggests.
Prostate cancer is often not life-threatening
A 10-year study involving 320 men by Baltimore's Johns Hopkins University found it can be safe to delay surgery.
The risk of noncurable prostate cancer was the same for men waiting two years for surgery as for those who had surgery immediately, researchers said.
Details appear in the Journal of the National Cancer Institute.
Noncurable prostate cancer is defined as a less than 75% chance of remaining disease-free 10 years after surgery.
Lead researcher Professor Ballentine Carter said: "This study suggests that for carefully selected men with prostate cancer who are monitored, the window of cure does not close in the short term.
"For those men diagnosed with early-stage, low-grade prostate cancer, an alternative to immediate surgical treatment would be careful surveillance."
Men screened for prostate cancer with the prostate specific antigen (PSA) test are on average diagnosed with the cancer 10 years earlier than men not undergoing PSA screening.
But while early diagnosis may help cut some patients' risk of dying from the disease, it can also lead to invasive treatments of a cancer that may never present a health risk to the patient.
Professor Carter says Hopkins has been enrolling patients in a monitoring programme since 1995 with great success, although some patients prefer to go ahead and pursue invasive treatment for "peace of mind".
"We hope this study will illustrate that in many cases a safe alternative to immediate treatment is surveillance."
The research focused on 320 men with low-grade tumours. Of these 38 had their surgery delayed for an average of just over two years.
However, their risk of developing noncurable cancer was the same as a group of 150 patients who had surgery after an average of three months.
The Johns Hopkins team is now studying blood and tissue samples to try to determine what might put patients at risk while they are being monitored.
Dr Kat Arney, of charity Cancer Research UK, said: "In the majority of cases it is best to treat cancer immediately, but this isn't always the best option for prostate cancer.
"Treatment for the disease can lead to serious and long lasting side effects.
"The major challenge is knowing which are the dangerous cancers that should be treated quickly, and which ones are safe to leave.
"Developing ways to predict how prostate cancer will progress is a key area for cancer researchers.
"Although these results suggest it is as safe to 'watch and wait' as to actively treat the disease, other studies have found that swift treatment is more effective.
"It is important for individual prostate cancer patients to discuss all the options with their doctor."
Dr Chris Parker, an expert on prostate cancer at the Institute of Cancer Research, said: "This is a useful study that provides further evidence that active surveillance with selective delayed intervention is an attractive option for men with good risk prostate cancer."