This study explores whether recurrent breast cancer can be safely treated with breast-conserving surgery and repeated radiation therapy in cases where patients have previously undergone radiation. Traditionally, recurrent breast cancer has been treated by removing the entire breast. However, recent research has shown that in certain situations, it may be possible to preserve the breast.

The study will collect data on the safety of this treatment approach and its effects on patients. The treatment follows standard breast cancer care practices, involving 30 patients from Helsinki and Turku University Hospitals. Patients are carefully selected based on specific criteria, such as tumor size, localization, and prior treatment history. Special attention is given to the planning of radiation therapy and surgical techniques.

The goal is to develop new treatment strategies that allow breast preservation even in cases of recurrent breast cancer, providing patients with high-quality and individualized care.

Inclusion Criteria:

• The patient has a diagnosed breast cancer or tumor area in the breast with a maximum diameter of 3 cm, where a previous breast-conserving surgery has been performed (either invasive breast cancer or carcinoma in situ, DCIS).

The patient has only a local recurrence, and imaging studies show no suspicion of metastases outside the breast (preoperative staging N0M0).

At least 3 years have passed since the completion of prior radiation therapy. The new breast cancer can be technically treated with another breast-conserving surgery using a technique that does not require tissue transfer from areas opposite the removed tumor to restore the shape of the breast.

The patient is at least 55 years old at the time of surgery. The patient is willing to participate in the study. The patient is capable of providing informed consent.

Exclusion Criteria:

• A booster dose, also known as a "boost," was administered during prior radiation therapy.

Preoperative assessments suggest multifocal breast cancer, with the tumor area to be removed exceeding 3 cm.

The planned radiation therapy per the study protocol cannot be administered due to factors such as shoulder joint stiffness, a pacemaker located in the radiation field, or a skin condition (e.g., scleroderma).

The patient is unable to provide informed consent or is unwilling to participate in the study.

Metastases outside the breast (e.g., axillary or distant metastases) are present.