BACKGROUND This paper presents two cases of very rare tumors of breast: breast sebaceos carcinoma, which has rarely been described in medical literature, and breast carcinosarcoma. Morphological characteristics and biological behavior of sebaceos carcinoma are still rather vague. Carcinosarcoma of the breast is a rare malignancy with distinct cell lines described as a breast carcinoma of ductal type with a sarcoma-like component. METHODS The first presented case is a 73-year-old female referred to our hospital in January 2008 with tumor of the right breast in the upper outer region of the breast and enlarged lymph nodes in the right axillary region. The second presented case is a 51-year-old female with carcinosarcoma, also a very rare primary breast tumor. She was admitted to our hospital in June 2011 with history of lump in the upper and lower outer quadrant of the left breast. In both cases, biopsy of tumor tissue was carried out with a thin needle, i.e. the aspiration cytology was applied as a diagnostic method, and during the operation the fast diagnostics of frozen sections and cytologic diagnostics were done. Although this methodology is important in diagnosis, in both cases it showed certain limitations in diagnosing such rare tumors. The final diagnosis was made after carefully synthesizing the histological findings and immunohistochemical phenotype. CONCLUSIONS An accurate classification of breast tumors on cytological preparations is not possible in case of poorly differentiated and rare tumors. A careful and accurate classification of these tumors is necessary.