At the opening of Sandra Lee’s new documentary, she confronts her own harsh, new reality.

“You actually have breast cancer. Cancer,” the 52-year-old says, sounding incredulous.

“That word will put the fear of God in you like you’ve never felt before. But you don’t realize what that feels like inside your body until it’s about you.”

In “RX: Early Detection — A Cancer Journey with Sandra Lee,” premiering Monday on HBO, the “Semi-Homemade” chef aims to make the viewer share her experience as closely as possible.

Lee, the de facto first lady of New York, was diagnosed with an early form of breast cancer in 2015, following a routine mammogram. That’s when she decided to have a camera chronicle her harrowing journey, including a double mastectomy, and the immediate aftermath.

The result is a low-production, high-impact ad for early breast-cancer screening.

Lee lets the filmmakers show her at her most vulnerable moments as she searches for doctors, seeks out the most effective treatments and questions experts about why the vicious disease chose her, someone whose family history wouldn’t seem to predispose her to breast cancer. (Although, her great-grandmother did have breast cancer.)

At one point, she expresses eagerness to get rid of her breasts and mitigate the chance of the cancer spreading. After all, she felt lucky her doctors caught it when they did.

“If you’re not in the right place at the right time and you don’t catch it, it’s the scariest disease,” she says.

Sandra Lee’s sister, Kimber, visits Lee in the hospital during her mastectomy.From the documentary “RX: Early Detection — A Cancer Journey with Sandra Lee”

It also may be among the least glamorous. This documentary forgoes any attempt to pretty up the proceedings. There’s no flattering lighting—just the stripped-down, clinical reality of doctors’ offices and hospital rooms.

Lee built a cookbook empire on the premise that one could create a home-run meal by starting on second base, combining fresh items with store-bought ones like canned mushroom soup and commercial tomato sauce. As this documentary makes clear, there are no shortcuts to treating cancer — but there can be great leaps of faith. Some of the most shocking scenes follow Lee’s painstaking decision to have a double mastectomy.

The cameras follow her into the operating room, and continue to run even as doctors remove Lee’s breast tissue.

A post-surgery scene isn’t any less gruesome, as she shows the bloody drains coming from her chest. At one point, she suffers a brutal coughing fit. Even so, Lee finds peace with her decision once she speaks to her doctors.

“They said they found more cancer when they were in there that wasn’t identified in the mammograms, so I did the right thing in taking everything out,” she says.

“I know that that’s true, but I don’t feel very good right now.”

The film also offers a glimpse into her decade-long relationship with Gov. Andrew Cuomo, who accompanies a crying Lee into the operating room.

Once inside, he announces to the doctors and nurses, “I’m Andrew. I’m in charge of moral support.” He then gives Lee a pep talk and tells her how much he loves her.

There are lighter moments, too.

Gov. Andrew Cuomo with Sandra Lee in March.Hans Pennink

On the morning of her surgery, Lee and Cuomo argue over lasagna — a controversial topic dating back to 2010, when Cuomo’s mother, Matilda, trashed Lee’s family recipe.

“Let’s not raise the lasagna conversation,” he says to the camera. Lee recounts how her sister Kimber brought a dish of lasagna that he called “meat casserole.”

“It was not a lasagna,” he insists, adding, “Nice. But different.”

Lee’s own story comes full circle when, a few months after her surgery, she makes her first public appearance at the 2015 Emmys in a blush ball gown with a plunging neckline. (She later had reconstructive surgery.)

“I bought this dress three years ago in London, and I could never fit into it because I had too big of boobs,” she says. “And now that I don’t have a top, I can wear my dress, so I’m very, very happy.”

That September she appeared on “Good Morning America” to declare herself cancer-free.

“Early detection,” she says, “is everything.”