Harry Connick Jr. and his wife Jill Goodacre reveal her breast cancer battle

— -- Harry Connick Jr. and his wife, Jill Goodacre, revealed to People magazine that she was diagnosed with breast cancer in 2012.

Goodacre explained to the magazine that after a routine mammogram and sonogram, she was diagnosed with stage 1 invasive ductal carcinoma.

Her treatment included a lumpectomy, radiation and Tamoxifen, a medication used to treat the disease.

“I was scared I was going to lose her, absolutely,” Connick Jr., 50, told the magazine. “I wasn’t going to let her see that, but I was. I know from losing my mom [from ovarian cancer when he was 13] that the worst can happen. She’s my best friend, and I really don’t know what I would do without her.”

Now in remission, Goodacre, 53, said that she's still nervous about the cancer coming back. However, the model and mother of three daughters told the magazine that reaching the five-year mark was a major milestone.

“It wasn’t like we were superstitious, like if we said something about being in the clear we’d somehow jinx it,” Goodacre said. “But we wanted to be well on the other side of things before we told everybody. The doctors all say that after the five-year mark, things look optimistic, so we’re starting to feel pretty good.”

Goodacre also told People magazine that her breast cancer was initially missed during a routine mammogram, and was not spotted until she had an ultrasound.

"Jill was told that she has dense breasts, [and] it was recommended that she also have an ultrasound following the mammogram," Kate Coyne, the executive editor of People magazine, told ABC News. "The technician saw something that didn't look good." Coyne described Connick Jr. as "putting on a game face" so support his wife.

"Harry, for Jill's sake, had a very stoic demeanor. He absolutely put on his best game face," she said. "Privately, however, he said that he was just absolutely terrified."

Goodacre told the magazine that she had "never heard about dense breasts."

"If I'd only had a mammogram and walked away for the next year, things could have turned out so differently for me," she added.

There is no perfect screening test when it comes to detecting breast cancer, Dr. Jennifer Ashton, ABC News' chief medical correspondent, said today on "Good Morning America."

"Mammograms, we know they can miss cancers that can show up on sonograms, especially on women with dense breasts, because tumors look white and dense breasts look white," Ashton said. "These imaging tests are not one-size-fits all. They're not all tests for every women."

She continued, "They all have their pros and cons and that has to be discussed doctor to patient before that prescription is written, before you go for that test."

In general, mammograms are the recommended screening test for women with an average risk of developing breast cancer, according to Ashton. Sonograms, however, can be useful for women who have dense breasts, and MRIs are often recommended for women with a high risk of developing breast cancer.