I forgot to mention about incidental prostate cancer. The incidental prostate cancer is when the prostate cancer is found by accident when they were examining a patient for non prostate cancer related diseases. University of Southern California and University of Iowa did such studies based upon the patients who had radical cystectomy.
University of Southern California checked 1,476 patients who underwent RCP (radical prostatectomy) between 1970 and 2008 for urothelial carcinoma of the bladder (without prior known history of prostate cancer), 559 patients (38%) were identified to have incidental prostate adenocarcinoma. Please note is seems that the procedure to remove the prostate including during radical cystectomy for bladder cancer is called RCP(radical prostectomy). Anyway, 38% of bladder cancer patients who had removed the bladder happened to have prostate adenocarcinoma.
University of Iowa found that 34% of the bladder cancer patients who had radical cystectomy was found to have prostate cancer (adenocarcinoma).
A study looking at autopsy of general public who were not known to have prostate cancer before they died found prostate cancer from 5% at age of 30 and under and 59% at age greater than 79 years old. So the data from USC and University of Iowa make sense because 1 in 9 males will have prostate cancer according to American Cancer Society website and 90% of bladder cancer patients are over 60 years old at the time of the initial diagnosis.
So, though they found a lesion by MRI which was done because of the rise in the PSA value of your husband, high percentage of males - seniors have prostate cancer anyway regardless of the status of other disease, including bladder cancer. Please note that many prostate cancers are slow growth and will not affect much the patients. It is known that many men die with other causes without knowing that they had prostae cancer.
This is another reason I think the lesion found is prostate originated.
Link to the paper by Univesity of Iowa regarding incidental prostate cancer of bladder cancer patients who removed the bladder.
www.ncbi.nlm.nih.gov/pmc/articles/PMC5031900/
Link to the paper which investigated the incidental prostate cancer of those who died for other reasons.
www.ncbi.nlm.nih.gov/pmc/articles/PMC4682465/