The actress, 44, said that when she first received the news, all she could think about was how her family would cope.
"You worry most about the people that you love and making sure that they are going to be okay. For me, that was the hardest part," she told Dr. Mehmet Oz, tearing up.
Doherty said she delayed going to a doctor even though she had felt a lump in her breast because her business managers had failed to pay her health insurance. (She is currently suing her former business managers for alleged misconduct.) She encouraged women who felt irregularities not to delay going to the doctor as she did.
"You have no idea what that extra time might have afforded you," she said. "Mine for instance spread to a lymph node or two. It might not have spread ... The most important thing is catching it as early as humanly possible."
Doherty said the mass is still in her breast, and she has not had surgery yet, as her oncologist felt that they should see if a medicine regimen would shrink the tumor. The actress' tumor feeds on estrogen, so the treatment has involved blocking the hormone.
RELATED VIDEO: Meet the Girl Who's Helping Families Impacted by Breast Cancer Through Photography
"I'm 44 and my husband and I wanted children," she said, adding that because of the treatment, the couple is more likely to adopt than have biological children.
Doherty's husband Kurt Iswarienko said the cancer has been a test for their marriage.
"For us, it has brought us closer together. It's one of those times you get to test your mettle as a married couple," said Iswarienko.
Doherty, who plans on getting the surgery soon, said she is getting used to the idea of a possible mastectomy, though no decisions have been made.
"They're just breasts," she said. "In the grand scheme of things, I would rather be alive and I would rather grow old with my husband."
Doherty exclusively revealed to PEOPLE in August that she was battling breast cancer.
"I am continuing to eat right, exercise and stay very positive about my life," she said at the time. "I am thankful to my family, friends and doctors for their support and, of course, my fans who have stood by me."
The Dr. Oz Show airs weekdays (check local listings).