A man who suffered with a painful erection for an entire week was forced to have half his penis amputated after doctors discovered an aggressive cancer.

The unnamed patient, 52, waited a full seven days before he visited his doctor , where he explained that his erection began without any sexual stimulation whatsoever.

He told medical professionals that his penis hurt so much it felt like it was "about to explode".

Doctor Wang Hung-jen, head of Kaohsiung Chang Gung Memorial Hospital's Urology Department, said the patient's constantly erect penis was caused by late-stage bladder cancer, which had metastasised and caused tumours to obstruct blood vessels in his penis.

A check-up three years ago had actually revealed early stages of the cancer , Doctor Wang noted, saying that he advised the man to have his bladder surgically removed.

He added:

Wang and a team of surgeons operated on the man and cut into his penis and bladder in order to relieve some of the pressure build-up causing the pain.

However, they found the tumours had spread too far and in the end had no choice but to remove half of the patient's penis.

The man, from Kaohsiung City in south-western Taiwan, is now recovering from the operation but will begin courses of chemotherapy as early as possible.

Wang has advised visiting one's doctor if experiencing an erection that lasts over four hours, saying that a 72-hour erection could cause permanent damage and result in lifelong erectile dysfunction.

On whether his patient was likely ever to have sex again, Wang said: