A new study has identified the highest risk symptoms that can indicate testicular cancer, in research that aims to improve diagnosis.
Testicular cancer is on the rise in the UK, with well over 2,000 new cases each year.
The number of cases has increased by 27% since the late 1990s, and is expected to grow by 12% over the next two decades.
The research, by the University of Exeter Medical School, published in the British Journal of General Practice has found testicular enlargement (a lump or swelling) to be the biggest risk factor for testicular cancer.
The finding that painful testicular enlargement may indicate cancer contradicts traditional teaching.
The study, led by Dr Elizabeth Shephard and Professor Willie Hamilton is the first to look at symptoms of testicular cancer reported in UK general practice (GP) surgeries.
The research was funded by the National Institute for Health Research.
Dr Elizabeth Shephard, of the University of Exeter Medical School, 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."
The study compared anonymised patient records of 1,398 men with testicular cancer to 4,956 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.
Professor Willie Hamilton, of the University of Exeter Medical School, 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.
"We design the risk assessment tools we use in our studies to help GPs assess risk in 20 cancers and we're rolling out this work as part of efforts to help improve the number of lives that can be saved."
The findings support current National Institute for Health and Care Excellence (NICE) guidelines, and may help doctors decide when an ultrasound should be considered in men with symptoms of testicular cancer.
Source: University of Exeter