Ductal carcinoma in situ (DCIS) is an extremely heterogeneous disease in terms of clinical manifestations, morphological changes, and expression of biomarkers, which determine the risk of subsequent development of an invasive breast cancer (BC). Diagnosis and treatment of DCIS prevents the development of invasive tumors (which reduces the potential risk of death from BC); however, the prognostic value of local treatment depends on the biological characteristics of its. The tumor grade, presence of comedonecrosis and expression of estrogen receptors are the key prognostic factors in DCIS for the treatment tactics and prognosis. The clinical symptoms of DCIS are very scarce, the most of tumors is diagnosed by screening mammography; the typical sign of DCIS is malignant microcalcifications or changes of breast architectonic. The sensitivity of mammography, ultrasound and MRI directly depend on the biological characteristics of DCIS. Surgical treatment (breast-conserving surgery or mastectomy) significantly reduces the risk of BC death in women with DCIS G2/G3, and radiotherapy after breast-conserving surgery reduce the risk of local recurrence of non-invasive and invasive BC. The choice of the local treatment (breast-conserving surgery radiation therapy vs mastectomy) depend on such factors as: tumor size, localization, clear margins, and biological characteristics of DCIS. In contrast to invasive cancers, the negative margin in DCIS is more than 2 mm from the tumor. Regional lymph node involvement in DCIS occurs in less than 1% of cases; however, microinvasion is found in analyze the surgical specimen in 15% of patients, which raises the question about regional staging. Risk factors for microinvasion in DCIS are age less than 55 years, tumor lesion size more than 4.0 cm, DCIS grade G3, and tumor palpability. Adjuvant endocrine therapy with tamoxifen significantly reduces the 10-year risk of invasive recurrence by 51%, the risk of contralateral BC by 50% and the risk of death by 40%, but only for hormone-positive DCIS. HER2 overexpression is found in DCIS significantly often (up to 40% of cases) than in invasive BC, HER2+ status correlates with DCIS high grade G3, the presence of comedonecrosis and with increased risk of relapse (both non-invasive and invasive) but is not a reason for anti-HER2 therapy. DCIS low risk and DCIS high risk have not only different morphological characteristics, but also different models of biological behavior, which must be considered in the different choice of treatment tactics.
