"Libby" was covered in tumors from head to tail, including some the size of tennis balls, when she was abandoned in Van Nuys on Wednesday.
A woman was seen on surveillance footage tying the 9-year-old pit bull mix's leash to the door of Pet Orphans, leaving some food and walking away.
"I've seen some sights, but nothing like this," said her rescuer, Tina Marie Lythgoe, of the Sun Valley-based animal rescue organization Josh and His Critters.
"(It's) abuse, big time, just to let her get in this condition," Lythgoe said.
Lythgoe said she plans to take Libby to an oncologist to see what can be done for the animal.
More information on Josh and His Critters is available online.
Kimberly Cheng reports for the KTLA 5 News on Jan. 16, 2020.