Yes - I had both BPH (an enlarged prostate) and was diagnosed with an aggressive prostate cancer (PCa) in 2013. My GP had been treating me for BPH for several years prior to diagnosis. I was getting up several times a night to pee and also reported a weak stream. When my PSA reached 2.3 my GP suggested I "might" want to visit with a urologist. Thank God I did when I did.
If you have cancer and decide on surgery, your entire prostate or portion of it will be removed. A strong stream should return and did in my case. IF you decide on some form of radiation, the treatment can shrink tumors in the prostate and flow could improve. If the physical size of the prostate remains, the mass can present urine flow issues and could require additional treatments or perhaps a Transurethral Resection of the gland or TURP in the future.
The two issues of BPH and PCa are entwined. Your urologist is the one who is best equipped to answer your medical questions based on your individual and specific situation. Dennis(ProstateCancer.net TEAM)