A single dose of the drug carboplatin is as effective at treating testicular cancer as two to three weeks of radiotherapy.
Researchers say the drug could become the preferred treatment for the most common type of testicular cancer, and might eventually allow surgeons to remove just the affected part of a testicle, rather than the whole organ.
The study, found that just one single dose of carboplatin in the short term is as safe as radiation and it's less toxic.
Lead researcher Professor Tim Oliver, from Barts and Queen Mary's School of Medicine and Dentistry, says almost 2,000 men in the UK are diagnosed with testicular cancer each year and the number has doubled in the last 30 years.
When most men are diagnosed, the cancer is confined to the testis, and known as Stage I of the disease.
The most common type of Stage I testicular cancer is seminoma, for which the usual treatment is surgery followed by a course of radiotherapy, and although radiotherapy is extremely effective in preventing recurrence of the cancer, there are potential side effects.
In the short term there is the 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.
This latest study compared almost 1,500 patients treated either with radiotherapy or carboplatin, and it was found that a single injection of the drug was as effective in preventing recurrence as two to three weeks of daily radiotherapy.
It was also found that two years after treatment 97.7% of the carboplatin group were free of cancer, compared to 96.7% of the radiotherapy group.
The researchers also found that 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.
It also appeared that they were less likely to develop tumours in the remaining testicle, and that risk was one in 200 in the carboplatin group, compared with one in 50 in the radiotherapy group.
Professor Oliver, says this large trial clarifies, after 20 years of research and uncertainty, that one dose of carboplatin in the short term is as safe as radiation and is less toxic.
He suggests the findings 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 Medical Research Council's Clinical Trials Unit says they will need to follow patients for several more years before they can be certain that tumour recurrence has been prevented rather than just delayed.
She says the results are nevertheless extremely encouraging, and are particularly good news for those countries where radiotherapy equipment is scarce.
The study was funded by the Medical Research Council, and is published in The Lancet.