Multimodal imaging with FAPI-PET/MRI for the detection of occult invasive breast cancer in DCIS

Ductal carcinoma in situ (DCIS) is an early precancerous condition of the breast in which the abnormal cells are confined to the milk ducts and have not yet invaded the surrounding tissue. About half of these cases eventually progress to invasive breast cancer, in which the cancer cells can spread into the surrounding tissue.

DCIS is usually detected during a routine mammogram, as it generally does not cause any palpable lumps or symptoms. To confirm the diagnosis, a tissue sample (biopsy) is typically taken. However, in about a quarter of cases, a biopsy may fail to detect existing invasive tumor components. Since it is currently impossible to predict with certainty whether a DCIS has already progressed to an invasive tumor, the suspicious tissue is usually surgically removed as a precaution.

To avoid unnecessary procedures and improve diagnosis, the MI-CISDIR study is investigating a new imaging technique: the so-called FAPI-PET/MRI. This technique combines two methods: positron emission tomography (PET), which visualizes metabolic processes in the body, and magnetic resonance imaging (MRI), which provides highly accurate anatomical images. Before the examination, a weakly radioactive substance ([68Ga]Ga-FAPI-46) is administered, which specifically binds to structures typically found in tumors. This allows for particularly precise visualization of tissue suspected of being tumorous. Currently, FAPI-PET/MRI is not yet approved for routine clinical use, but it is being intensively researched in scientific studies such as this one and is showing promising results.

The goal of this Phase 2 study is to determine how reliably this procedure can detect hidden invasive tumors (occult carcinomas) compared to the current standard method, biopsy. The examination is performed as part of the regular treatment planning process and takes about 45 minutes, including a short break. After the study is completed, the imaging results will be compared with the final surgical findings to evaluate the accuracy of the procedure. The study is single-arm and open-label, meaning that all patients know which test they are receiving.

Eligible participants include women and men aged 18 and older with newly diagnosed DCIS larger than 4 cm who are scheduled for surgery. Pregnant women, breastfeeding women, individuals with contraindications for MRI (e.g., metal implants, contrast agent intolerance) or impaired kidney function (GFR < 30 mL/min) are excluded from participation. Reliable contraception is required for the duration of the study, which lasts approximately 1.5 months. In addition to the imaging, a follow-up appointment is scheduled.