Longtime WBZ-TV reporter Bill Shields shared some unhappy news with colleagues and friends Monday. In an e-mail to news director John Verrilli, which was then forwarded to station staff, Shields revealed he has cancer. “You know how life is full of irony . . . sometimes it makes you laugh, sometimes it can anger you,” he wrote. “Well, I find it frustratingly ironic that after finally quitting smoking (the 100th time), I have been diagnosed with lung cancer.” But Shields sounds determined to beat the disease. “Within a few days I will unleash my own aggression on the cancer. I start chemo and radiation at Dana-Farber next week. . . . You guys know me . . . yet you might not know this: underneath my easygoing laughter is a street fighter (a few have witnessed it). . . . I will fight this with everything I have, and win.” Shields, a general assignment reporter for WBZ-TV, joined the station in 1980, twice winning New England Emmy Awards. He was at work Monday covering the case of former Patriots tight end Aaron Hernandez. Reached afterward, he told us he sent the e-mail because he wanted people to know the truth. “I’m probably going to disappear for a few months and I wanted people to know why,” he said.