Shannen Doherty

Shannen Doherty thanks Sarah Michelle Gellar for always having her back as she battles cancer

On Wednesday, Gellar made sure to raise awareness around International Breast Cancer Day by shouting out to Doherty—who is currently battling the disease—and her oncologist, Dr. Lawrence Piro, in a sweet Instagram post.

Shannen Doherty reveals her cancer has spread

"I had breast cancer that spread to the lymph nodes, and from one of my surgeries we discovered that some of the cancer cells might have actually gone out of the lymph nodes," Doherty said. "So for that reason, we are doing chemo, and then after chemo, I'll do radiation."

Doherty, who was diagnosed with breast cancer in February 2015, called the mastectomy "traumatic and horrible." But said the trauma of the surgery hit her when she got fitted for a new bra.