A single dose of a drug is as effective at treating testicular cancer as two to three weeks of radiotherapy, research has found.
Scientists say carboplatin could become the preferred treatment for the most common type of testicular cancer.
It might also eventually allow surgeons to remove just the affected part of a testicle - rather than the whole organ.
The study, funded by the Medical Research Council, is published in The Lancet medical journal.
Nearly 2,000 men in the UK are diagnosed with testicular cancer each year and the incidence has doubled in the last 30 years.
Most men are diagnosed when the cancer is confined to the testis, known as stage I disease.
The most common type of stage I testicular cancer is seminoma, for which the standard treatment is surgery followed by a course of radiotherapy.
Radiotherapy is extremely effective in preventing recurrence of the cancer, but there are potential side effects.
There is a short term risk of temporary infertility and gastric irritation, and in the longer term more serious problems can include damage to the cardiovascular system and a slightly increased risk of developing new primary cancers in other organs.
The latest study compared nearly 1,500 patients treated either with radiotherapy or carboplatin.
A single injection of the drug was as effective in preventing recurrence as two to three weeks of daily radiotherapy.
Two years after treatment 97.7% of the carboplatin group were free of cancer, compared to 96.7% of the radiotherapy group.
In the three months after starting treatment, patients treated with carboplatin took less time off work and suffered substantially less lethargy than those having radiotherapy.
They also appeared to be less likely to develop tumours in the remaining testicle.
The risk was one in 200 in the carboplatin group, compared with one in 50 in the radiotherapy group.
Lead researcher Professor Tim Oliver, from Barts and The London, Queen Mary's School of Medicine and Dentistry, said: "This large trial establishes, after 20 years of research and uncertainty, that one dose of carboplatin in the short term is as safe as radiation and it's less toxic.
"It might also open the way to enabling lumpectomy surgery for stage I seminoma and using chemotherapy for testis conservation."
Sally Stenning, senior statistician at the MRC Clinical Trials Unit said: "We will need to follow patients for several more years before we can be certain that tumour recurrence has been prevented rather than just delayed, but these results are nevertheless extremely encouraging.
"They are particularly good news for those countries where radiotherapy equipment is scarce."