I agree with gingernut.
The main risks for bladder cancer these days are smoking, smoking and smoking, followed by chemical and industrial exposure to aniline dyes, solvents and rubber industry.
The most likely explanation is going to be the fact that because of your mandatory medicals, the chance finding of microscopic blood in the urine will be made and then investigated. The implications for your employment / licencing, of such a diagnosis are also higher in your profession, and thus will be much more of a discussion point. So we have to stick to the data rather than anecdotes / vox pops and such.
All the best though and good luck with your treatment.
The plumber.