A sweet elderly pit bull was left tied to a tree in Queens with a bloody gaping chest wound — and it’s still a mystery who ditched the sickly pooch.

The poor 8-year-old dog was left for dead with advanced-stage mammary cancer near Atlas Mall in Glendale Tuesday, according to City Council members Bob Holden and Joann Ariola.

Neighbors reported the abandoned dog to the lawmakers after confusion about whether the call was a police matter — and bystanders rushed her to a shelter with help from the rescue group Lend-a-Paw, according to a council source.

“[A rescuer] had suspected that she had just given birth due to the amount of blood she was covered in. The dog was clearly in distress and in a lot of pain since she was growling and not allowing anyone to touch her,” Lend-a-Paw wrote on its Facebook page.

The pit bull, which they named Star, was in so much pain due to an “ulcerated and necrotic tumor” she was ultimately euthanized upon a vet’s recommendation, the group said.

“Animal cruelty in our city must be taken seriously, and the heartbreaking case involving Star is a perfect example of how these issues tragically fall through the cracks,” Holden said in a press release.

“It’s devastating and outrageous that someone would leave this poor dog tied to a tree, suffering from advanced-stage cancer, and we demand accountability for these despicable actions and urge the NYPD to ensure swift justice,” he said.

A council source said police initially said the case wasn’t a police matter, leaving the locals who found the ailing dog to take it to animal rescue.

Holden and Ariola said Star’s sad story should spark changes within the NYPD, including clarifying investigation procedures and offering officer education — so crimes against animals get more attention.

As it stands, NYPD policy often discourages officers from helping abused pets, said Ariola.

“The current procedure required for the NYPD to open an investigation is needlessly complex and antiquated, and most officers themselves are not even sure of the proper steps that need to be taken in animal cruelty cases,” she said.

“We will not let Star’s awful death be in vain. We need to see changes now, to protect the animals of this city from further harm.”

Police eventually showed up to the tree where the dog was abandoned — after pleas from Ariola and Holden’s office — but she had already been rescued, a council source said. A police spokesman said cops took the ailing dog to animal rescue, contrary to the council source’s description.

The NYPD has since opened an investigation into who left the animal there, he and police said.

-Additional reporting by Amanda Woods