Mesodermal mixed malignant tumours (MMMT) are the rare neoplasms of postmenopausal women, with extremely poor prognosis. They constitute about 1-2% of all gynaecological malignancies and about 2-5% of uterine corpus malignancies. Due to rare frequency, the exact knowledge about their characteristics is difficult. Therefore, the treatment is based on the treatment methods used in endometrial cancer. For most authors, because of their clinical course, they are treated as more aggressive endometrial carcinomas. In the literature, there were described a lot of cases of endometrial cancer and MMMT development after the chronic therapy with tamoxifen, due to breast cancer, but rare data suggest the possibility of coexistence of the two above neoplasms, without the previous therapy with tamoxifen. In this paper, we present the case of woman, aged 78, with tumour mixtus mesodermalis malignus corporis uteri, coexistent with breast cancer, and unilateral lymph nodes metastases, coming from the uterine tumour, with no previous therapy. In the literature we did not meet any case of breast cancer, coexistent with MMMT with the axillary lymph node metastases of MMMT component.