The 56-year-old actress posted a selfie on Instagram on 15 September and gave fans a health update.
"So grateful and happy to be alive but sad that my hair fell out and is about 1 inch long now and looks cra cra," she wrote. "Anyone else have #hairloss due to #cancer? Talk to me. I feel you."
She added, "I am POST cancer. All good now. Hard journey, but I am HEALTHY, happy, and more present and grateful than ever. Thank you from the bottom of my ever expanding heart for all of your LOVE."
Marcia returned to social media a day later and explained the previous post had really empowered her.
"After posting a picture of myself here and uttering the words #cancer and #hairloss, I felt liberated, deliriously free and completely me," she wrote. "How or why this simple act gave me such a powerful lift I did not question, but I thanked God or whatever gave me the internal push to move forward and expose myself.
"I certainly wasn't expecting the response of love and kindness that flowed to me. My capacity to receive requires a massive expansion! I am ecstatically alive and what interests me post-cancer is #AUTHENTICITY. #VULNERABILITY. #TRANSPARENCY. And of course #LOVE."
It's not the first time Cross has faced and beaten cancer - her husband, Tom Mahoney, was diagnosed in 2009, and, like his wife, is now healthy.