The actor, who recently launched a lifestyle blog called AtHomeWithTheZierings.com, opened up to ET on Thursday about Doherty, who recently shaved her head in anticipation of her fight against her aggressive ailment, and documented the emotional process on Instagram.
"I gave her a call last week and just let her know that I was thinking about her," the 52-year-old Sharknado star revealed.
Ziering also praised the 45-year-old actress for "demonstrating her tremendous amount of bravery" by being so open and candid about her cancer fight.
"She's one tough cookie," he said. "If she could handle the press outlets that were roasting her [during her time on Beverly Hills, 90210], then I'm sure [she can beat] cancer."
"She can stand up to that, if anybody can," he added.
Fellow Beverly Hills, 90210 alum Jason Priestley spoke with ET on Wednesday where he shared Ziering's confidence in Doherty's bravery.
"Shannen's a strong kid and a tough fighter and I know that she's gonna come through this fight and she's gonna be OK," Priestley shared. Check out the video below to hear more.