Martinez died on March 6 at 12:05 p.m. The family decided to remove her from a life support machine because she wasn't getting better.
"She was surrounded by family and went peacefully. Our family would like to thank everyone for their prayers and support as well as ask for privacy during this time," the family posted on Facebook.
A funeral was held for the teen at St. Frances of Rome Church in Azusa Friday morning.
It all started while Sandra was cheerleading at a January basketball game. When she got home, she told her mother she was having a hard time breathing.
Her mom took her to the emergency room, where doctors found a large 7-inch cancerous tumor on her lungs. She then underwent a dangerous procedure for doctors to get a biopsy of the tumor. One of her lungs collapsed after she had internal bleeding, so doctors placed her in a medically-induced coma.