It has become apparent that estrogen receptor (ER) - positive and - negative breast lesions are completely distinct diseases. Precursors of low-grade breast cancer are low-grade premalignant lesions, usually ER and progesterone receptor (PR) positive and HER2 negative. On the other hand, precursors of high-grade breast cancer are high-grade premalignant lesions, usually ER and PR negative and HER2 positive. Lobular neoplasia (LN) and ductal carcinoma in situ (DCIS) are important from the clinical point of view. LN increases the risk of bilateral breast cancer. This is why the recommendation for the treatment of LN is very different – from just following‑ up up to bilateral mastectomy. The complete surgical excision of the lesion with negative margins is the usual treatment of DCIS. Several big randomized clinical trials showed the benefit of adjuvant radiotherapy (RT). Some of them suppose that there is a group of patients who do not need adjuvant treatment. The benefit of adjuvant tamoxifen is clear only for patients with ER positive disease. The UK/ ANZ study showed the benefit of tamoxifen only in patients without RT.