Dana-Farber Cancer Institute will enter a new phase in its budding partnership with Beth Israel Deaconess Medical Center next week, as the renowned cancer center transitions its breast oncology services away from Brigham and Women’s Hospital and toward Beth Israel.

Beginning Monday, Beth Israel and Dana-Farber, which announced their partnership in 2023, will each house different portions of the breast cancer treatment process, Dana-Farber said Thursday. Outpatient breast oncology services will be provided by Dana-Farber, while breast cancer surgeries will take place at Beth Israel Deaconess.

BIDMC is part of the Beth Israel Lahey Health system, the state’s second-largest hospital network, which competes with the state’s largest health system, Mass General Brigham. Dana-Farber shocked health care insiders when it broke up its longtime partnership with the Brigham, one of MGB’s flagship hospitals, to build a new cancer-only hospital with Beth Israel.

This treatment center transition will be the first of many for Dana-Farber as it unwinds its Brigham partnership, which ends in 2028.

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Dr. Elizabeth Mittendorf, who was formerly at Brigham, joined BIDMC in 2025 to lead the hospital’s new breast surgery division. At least two of the nine other surgeons in the division previously worked at Brigham, online records indicate.

“Breast cancer is not one disease, but rather a series of very specific subtypes that require different therapies and approaches, each tailored to the individual patient,” Mittendorf said in a statement. “As surgeons at BIDMC, we are working hand-in-glove with our colleagues in breast oncology at Dana-Farber, and radiation oncology, pathology, reconstructive surgery, and across other disciplines to deliver the best possible care and outcomes for our patients.”

Dana-Farber and Beth Israel are on the verge of breaking ground on a new 300-bed, $1.68 billion cancer hospital that will house patients who need in-patient care during their treatments. It’s slated to open in 2031. Meanwhile, Mass General Brigham is investing $400 million to create a competing cancer institute, with new construction and renovations across multiple locations.

For Dana-Farber, surgical care and recovery will still take place at BIDMC or another hospital, should patients elect to have their surgeries elsewhere.

“If a patient says, ‘I want to have my surgery in New York, or at Mass General, or in Paris, we work with those doctors. That happens all the time with our patients,” Dana-Farber Chief Executive Dr. Benjamin Ebert said in an interview. “In all cases, patients have the agency to choose who takes care of them.”

Dana-Farber said it is home to the largest portfolio of breast cancer clinical trials in New England, which includes trials for every type of breast cancer. BIDMC houses a number of surgical clinical trials, including research to improve breast reconstruction and to treat lymphedema, a common breast cancer side effect that causes swelling in the body’s lymphatic system.

Marin Wolf can be reached at marin.wolf@globe.com.