Aim of the study. Evaluation of long term results, the identification of the causes of the treatment failure and prog­nostic factors in women with early invasive breast cancer after breast conserving treatment.

Material and methods. 1425 women with an early invasive breast cancer after breast conserving treatment under­went postoperative radiotherapy in the Department of Radiotherapy of The Maria Skłodowska-Curie Memorial Cancer Center in Warsaw. Duration of the symptoms before diagnosis ranged from 0 (the tumor was found incidentally by mammography or ultrasound scan) to 84 months. In 1204 patients the size of the tumor did not exceed 2 cm. Most frequent localization was in external quadrants. 3 to 24 weeks after surgery all patients underwent breast irradiation with Co-60 or photons X 4–6 MeV in the dose of 42.5–50 Gy and next, 1405 of them received additionally 10–20 Gy to the site of the removed tumor, mostly with electrons of 9–15 MeV. In 489 the treatment was combined with chemo­therapy and in 592 patients with hormone therapy.

Results. The tolerance of the treatment was good. In 1357 (95%) women the cosmetic effect of the treatment was evaluated as very good and good. 15-years overall survival (OS) rate was 85% and disease free survival (DFS) rate was 79%. 15-years local recurrence rate risk was 6.9% and distant metastases occurred in 12.7%. Unfavourable prognos­tic factors were: size of the tumor being more than 2 cm (T2), metastatic axillary lymph nodes (N 1–2), ductal type carcinoma and beginning of the treatment before the year 2006.

Conclusions. Breast conserving treatment is a safe and well tolerated method providing a high percentage of overall and disease free survival as well as good and very good cosmetic effects. Failure of the breast conserving treatment is relatively rare and is mostly due to the generalisation of the disease. The prognosis in this group of patients depended on: the size of the primary tumor, presence of metastatic axillary lymph nodes, a ductal type of the cancer and timing of the beginning of treatment.