Mammary sarcomas are very uncommon and make up less than 1% of all primary breast malignancies [
1-
3].
Primary osteosarcoma of the breast is extremely rare and represents 12.5% of mammary sarcomas [
1].
The histogenesis of primary osteosarcoma of the breast is not clear, but an origin from totipotent mesenchymal cells of the breast stroma or a transformation from a pre-existing fibroadenoma or phyllodes tumor has been suggested [
2-
4]. Primary breast osteosarcomas are considered highly aggressive tumors associated with early recurrence and a propensity for haematogenous rather than lymphatic spread, most commonly to the lungs [
1,
2].
Mammographically, these tumors often present as a well-circumscribed dense lesion within the breast parenchyma with focal or extensive coarse calcifications[
1,
5]. The mammographic features may be deceptively benign [
1].
Osteosarcoma of the breast, similar to other extraskeletal osteosarcomas, may have a broad primary osteosarcomas of the breast are fibroblastic, osteoblastic, osteoclastic (giant cell-rich) and fibroblastic subtypes [
4-
6].
The diagnosis of metaplastic mammary carcinoma should be excluded before primary breast osteosarcoma is diagnosed. The term sarcomatoid carcinoma has been adapted to reflect the appearance of a mesenchymal neoplasm in these epithelial malignancies. The term carcinosarcoma has usually been used to describe biphasic tumors composed of distinguishable malignant epithelial and sarcomatoid components with heterologous elements [
4,
5].
A secondary lesion from a primary osteosarcoma of the bone should be considered in the differential diagnosis. In addition, the diagnosis of primary breast osteosarcoma similar to that of other extraskeletal tumors requires the absence of a direct connection between the tumor and the underlying skeleton [
7,
8].
Treatment for the localized disease should include complete surgical removal of the tumor with an adequate margin. Axillary lymph node dissection is not indicated because axillary node involvement is exceptional. Whereas, for the metastatic disease the chemotherapy basing on the classic drugs (doxorubicine, ifosfamide, cisplatinium, methotrexate) in the osteosarcoma is the main treatment [
8,
9].
Although no standard of care for these lesions has been made because the rarity of this entity [
1,
7,
9].