Randomized study was made of 254 women with breast invasive duct cancer (pT1N0M0). In 61 patients, organ sparing operation was followed by radiation therapy of either breast alone or zones of regional metastasizing (57 patients) as well, with or without adjuvant chemotherapy or hormone therapy (tamoxifen). It was found that radiation of mammary gland, with or without additional radiation exposure of zones of regional metastasizing, results in both decrease recurrence development (p < 0.05) and significant (p < 0.05) increase in recurrence-free survival in women who had tumor size within the range from 1 to 2 cm in diameter in contrast to patients with tumor size not exceeding 1 cm, whose survival was not positively influenced by radiation.