Evaluating the effectiveness and safety of a tumor bed boost after whole breast irradiation following breast-conserving surgery in patients with non-low-risk ductal carcinoma in situ.

This study investigated the effectiveness and safety of a tumor bed (where the tumor was present) boost after whole breast irradiation (WBI) following breast-conserving surgery (BCS) in patients with non-low-risk ductal carcinoma in situ (DCIS). The data showed that a tumor bed boost after WBI following BCS reduced local recurrence (return of the cancer at the original tumor location) with manageable side effects in these patients.

Ductal carcinoma in situ (DCIS) is an early stage of breast cancer in which the cancer cells are confined to the milk ducts. Due to increased screening measures, the rates of women treated for DCIS have also increased. DCIS is generally treated with mastectomy (surgical removal of the breast) or breast-conserving surgery (BCS; the removal of part of the breast) combined with radiation. DCIS is treated in order to reduce the risk of invasive breast cancer (IBC), the spread of cancer cells into the breast tissue.

Radiation therapy (RT) such as WBI is commonly used following BCS to destroy any remaining cancer cells. WBI therapy involves radiation treatment of the whole breast. After the RT, an extra radiation dose can be delivered to the place where the tumor was to prevent the recurrence of cancer. This is called a boost. Studies have shown that WBI after BCS in DCIS reduces local recurrence. However, whether a tumor bed boost after WBI following BCS improves outcomes in patients with non-low-risk DCIS remains unclear.

This study involved 1608 female patients. All the patients had non-low-risk DCIS which was treated with BCS. Patients were divided into two groups. Group 1 included 805 patients who received no boost after WBI. Group 2 included 803 patients who received a boost dose (16 Gy in eight fractions) after WBI. The average follow-up time was 6.6 years.

After 5 years, 92.7% of the patients in group 1 were alive without local recurrence (return of the cancer at the original tumor location) versus 97.1% of the patients in group 2. Boost dose after WBI reduced the risk of local recurrence by 53% compared to no boost.

Patients in group 2 experienced higher breast pain than patients in group 1 (14% vs 10%). Patients in group 2 experienced significantly higher hardening of the breast tissue than patients in group 1 (14% vs 6%).

This study showed that a tumor bed boost after WBI following BCS reduced local recurrence with manageable side effects in patients with non-low-risk DCIS.

This study did not collect data on compliance with hormonal therapy given after surgery.