A news study suggests that having a swollen testicle or discovering a lump is the biggest indicator of testicular cancer.
Research has found that testicular enlargement - either a lump or swelling - is the biggest risk factor for testicular cancer.
The finding that painful testicular enlargement may indicate cancer contradicts traditional teaching, the study authors said.
Testicular cancer is on the rise in the UK, with well over 2000 new cases each year.
The study, led by Dr Elizabeth Shephard and Professor Willie Hamilton from the University of Exeter, is the first to look at symptoms of testicular cancer reported in GP surgeries.
The study compared patient records of 1398 men with testicular cancer to 4956 controls in the year before their diagnosis, to determine which symptoms are associated with a higher risk of the disease.
Diagnosing the disease early often means shorter treatment times and fewer complications, and it may help to improve fertility.
Dr Shephard said: "We know early and accurate diagnosis saves lives in cancer.
"The findings of our study give greater clarity on which patients GPs should refer for further investigation for suspected testicular cancer in order to get the best outcome for patients."
Prof Hamilton said: "Despite recent improvements, the UK still lags well behind other countries on cancer survival.
"Our study showed that some cancers could be confused initially with other testicular conditions, likely leading to delays in diagnosis."
Dr Richard Roope, clinical lead for cancer at the Royal College of GPs, said testicular cancer was one of the most treatable types of cancer.
"This new research indicates a promising breakthrough in understanding the biggest risk factors for testicular cancer," he said.
"Any testicular swelling should be checked out by the patient's GP and these findings could assist GPs in better identifying symptoms of testicular cancer and knowing when to make an urgent referral so that men with the disease receive better outcomes."
The paper is published in the British Journal of General Practice.
