On June 6, 2009, Costello was diagnosed with Stage IV small cell lung cancer that had already spread to both lungs, her liver, breasts, ovaries, and bones. However widespread the cancer, she was physically fit, a nonsmoking, college athlete, and had only gone to the trainers office with slight pains in her abdomen days after coxing her boat to a second-place finish at NCAA. The gravely serious diagnosis she received from her initial stomach pain was shocking, and Costello's story spread quickly through her
CaringBridge website. Altogether, Costello underwent 21 rounds of chemotherapy and 14 radiation treatments. Costello spearheaded the first
Jog for Jill on February 7, 2010, on the UC Berkeley Campus. The race drew over 1,000 participants and raised over $45,000 for lung cancer research. This was the largest fundraiser ever for lung cancer at the time. She then spoke at
Genentech, a cancer research company, about finding a cure for cancer that would save lives. On June 20, 2010, four days before her death, Costello sent out a mass message on
Facebook and her CaringBridge page from her hospital bed, inviting everyone she could to participate in the upcoming San Francisco
BJALCF Walk in September in her honor. Her message was later used by the foundation to spread the word about the jog via
YouTube and was the start of the entire Jog for Jill and Jill's Legacy movements. ==Activism==