BPH (benign prostatic hyperplasia, commonly also called simply "enlarged prostate") is an extremely common condition that afflicts a large percentage of older men and only gets more common with age.
While BPH is not prostate cancer and cannot spread to other parts of the body like cancer can, it is still potentially dangerous.
The prostate is situated just below the bladder and surrounds the beginning of the urethra (the tube that carries urine from the bladder to the outside of the body). Because it occupies this important location, when the prostate enlarges, it can block the flow of urine from the bladder.
For most men, this results in symptoms like dribbling, urgency, or hesitancy when urinating. These symptoms are usually just nuisances early on.
BPH can become dangerous, however, when the bladder is completely (or nearly completely) blocked. If urine is impeded from exiting the body, pressure will build up behind the bladder and then will transferred to the kidneys. Severe kidney damage can then result. Ultimately, if kidney damage is severe enough, the man could die from the condition.
It's important to get any new or worsening urinary symptoms checked out by your doctor. BPH and prostate cancer are just two of the possible causes of these symptoms.
Kumar: Robbins and Cotran Pathologic Basis of Disease, 8th ed.