Black's husband Stephen Eckelberry has launched an online fundraising page to bring in the $17,000 (£10,000) needed to send the 73-year-old veteran star to Europe for a revolutionary new treatment.
The Natural Born Killers star is among a number of famous faces who have rallied together to support the Five Easy Pieces star, who Lewis has known since she was a child.
In a post on her Twitter.com page, Lewis writes, "My mentor... my creative mother, needs your help. I've known her since I could talk/dance/sing. She Always encouraged me. Karen Black was my first teacher. I played charades at her house when I was 6 years old. I bloomed because of her."
Alan Cumming, who co-starred with Black in 2007 movie Suffering Man's Charity, adds, "Please help! The legend Karen Black has cancer and can't afford treatment that will save her life."
True Romance star Patricia Arquette also shared a link to Black's fundraising page on GoFundMe, adding, "Actress Karen Black is fighting cancer... Help Karen in her battle."