Kelley Mack died at the age of 33 in August 2025 after battling a rare form of brain cancer. Her acting career had just gotten traction, with her performance in The Walking Dead being praised by fans. Mack’s multi-talented nature led her to pursue different projects, and she promoted her upcoming film work during the last months of her life.

Below, Hollywood Life explains the kind of cancer Mack was living with and what a glioma is.

Who Was Kelley Mack?

Mack was an actress, producer and voiceover artist. Per her IMDb profile, the Ohio native was best known for her performances in Broadcast Signal Intrusion, season 8 of Chicago Med and season 9 of The Walking Dead. 

Who Did Kelley Mack Play in The Walking Dead?

Mack played the character Addy in season 9 of The Walking Dead. 

What Form of Cancer Did Kelley Mack Have?

Mack revealed in January 2025 that she was diagnosed with a rare form of astrocytoma called diffuse midline glioma. Astrocytoma is a brain tumor, and diffuse midline glioma is a tumor that begins in either the brain or the spinal cord, per the National Cancer Institute.

“In September, I moved into a new apartment with my boyfriend, Logan,” the actress indicated in an Instagram caption at the time. “For a month after that, I had persistent lower back pain and thought I slipped a disc. A few weeks later, I had neuropathic itching in my right quad. And then, the shooting pains in my legs and back began, which resulted in me having to sleep in a recliner for a month because laying down was too painful. On Thanksgiving Eve, I had emergency MRIs done at the hospital, which revealed an abnormal mass in my spinal cord.”

Mack said that after her biopsy surgery on her spinal cord, she “lost the use of [her] right leg and most of [her] left leg,” so she had to use a walker and wheelchair to move.

Despite the mentally and physically strenuous ordeal, Mack maintained a positive attitude about her cancer journey and informed fans that her acting career would be “somewhat paused for a little” during her radiator treatment in Cincinnati, Ohio. Nevertheless, the Chicago Med alum noted that she had projects “coming out soon” and concluded that she was “determined and [knew] that this [cancer battle] will eventually be a short chapter in [her] long book.”

What Is a Central Nervous System Glioma?

A glioma is a malignant tumor that develops after glial cells grow too fast. Glial cells help the central nervous system function, according to the Cleveland Clinic.

There are three types of gliomas: astrocytomas, ependymomas and oligodendrogliomas. Astrocytomas can include glioblastomas and diffuse intrinsic pontine gliomas (DIPGs), per the Cleveland Clinic. Mack was diagnosed with an astrocytoma called diffuse midline glioma.

How Did Kelley Mack Die?

Mack died after her cancer battle, though an exact cause of death has not been disclosed at the time of publication.