Former NBA player Jason Collins has revealed he is battling stage 4 brain cancer.In an essay for ESPN, the 47-year-old said he has been diagnosed with stage 4 glioblastoma, one of the most aggressive forms of brain cancer.Collin s said he began experiencing symptoms over the summer and later learned he has a tumor that cannot be safely removed. He has decided to undergo a combination of radiation, targeted chemotherapy and immunotherapy.IN CASE YOU MISSED IT | Michael Strahan's daughter Isabella reveals she's cancer-free 9 months after discovering brain tumorStill, the average prognosis for glioblastoma is 11 to 14 months."If that's all the time I have left, I'd rather spend it trying a course of treatment that might one day be a new standard of care for everyone," Collins wrote.Collins said he wanted to share his diagnosis on his own terms just as he did when he publicly came out as gay.RELATED STORY | Researchers project an 84% increase in cancer cases among men by 2050He made history in 2013 as the first openly gay active player in NBA history.After I came out, someone I really respect told me that my choice to live openly could help someone who I might never meet, Collins wrote. Ive held onto that for years. And if I can do that again now, then that matters.Collins played 13 seasons in the NBA for seven teams, including the New Jersey Nets, Memphis Grizzlies and Boston Celtics. ...read more read less