It kills four men every day in London - 1,600 every year.
Many of them die because of embarrassment, ignorance or fear.
We're talking about prostate cancer and today ITV - in conjunction with Prostate Cancer UK - has launched "Stand By Your Man".
It's a campaign to raise awareness of the disease - to encourage men to talk about their health
Above all, it's to help save lives.
Nick Thatcher's report contains explicit descriptions about prostate cancer symptoms.