Primary osteosarcomas of the breast are very rare, aggressive, and heterogeneous neoplasms derived from non-epithelial elements of the gland and represent less than 1% of breast cancers and less than 5% of all sarcomas [1].

Its unusual presentation in the breast can put the pathologist in the dilemma of diagnostic. We report the case of a 71-year-old woman who was diagnosed with a primary osteosarcoma in her left breast. Through this case and review of the literature, we highlight several details of this rare histological type of breast cancer.

A 71-year-old woman, with no specific history, who presented with a lump in the left breast, discovered on self-examination, progressing gradually for one year. She was in good general condition with no other associated symptoms. The clinical examination showed a 7 cm mobile rounded mass in the outer quadrant of the left breast, without skin retraction and no palpable axillary lymph nodes (Figure 1).

Mammography revealed a voluminous dense opacity, focally with indistinct margin, containing microcalcifications in the outer quadrants of the left breast (Figure 2).

Ultrasonography (US) showed a large solid and cystic mass with indistinct margin containing microcalcifications, measuring 77 mm × 62 mm. Doppler evaluation demonstrated surrounding vascularity (Figure 3). The lesion was graded as highly suggestive of malignancy (Breast Imaging and Reporting Data System [BI-RADS] category 5).

A tru-cut biopsy was taken, which showed a malignant mesenchymal tumor proliferation, suggesting a fibro-chondro-osteosarcoma. The patient underwent a mastectomy.

The gross examination of the specimen from the left breast revealed a white beige neoplasm, well-circumscribed, firm, measuring 14×9×5.5 cm, focally hemorrhagic and necrotic (Figure 4). The histological examination showed a malignant spindle cell tumor with abundant osteoid substance and chondroid area. There were scattered multinucleated osteoclastic tumor giant cells. The carcinomatous component was not found (Figure 5). Multiple sections were taken to detect an epithelial component, thus ruling out the possibility of a metaplastic carcinoma. The immunostaining for cytokeratine AE1–AE3 showed no epithelial component (Figure 6).

Carcinoma is the most common malignancies of the breast and sarcomas form a minority of breast neoplasms. Primary sarcomas of the breast account for <1% of all primary breast malignancies [2]. Among those, osteosarcoma is extremely rare.

Approximately, 150 cases of this pathology have been reported in the literature since 1957 [1]. The histogenesis of primary breast osteosarcoma remains unclear. Still, an evolution from totipotent mesenchymal cells of the breast stroma or a transformation from a preexisting fibroadenoma or phyllodes tumors have been suggested [1],[3].

The presentation of breast osteosarcoma usually occurs at an advanced age, in contrast with skeletal osteosarcomas where the patients are younger. The majority of the cases are in patients that are over 60 years old with a reported median age of 64.5 years [2]. Risk factors for extraskeletal osteosarcomas have not been identified to date, although some instances have been attributed to local irradiation, trauma, or the presence of a foreign body [2].

The present patient was 71 years old with no history of trauma or irradiation, no tumor in other sites. Clinically, breast osteosarcomas often present as rapidly enlarging masses. Rarely, patients report associated bloody nipple discharge or nipple retraction [4].

Mamographically, these tumors often present as well circumscribed, dense lesions within the breast parenchyma, with focal or extensive coarse calcifications [3],[5].

The border may be regular or irregular. The mammographic appearances may be deceptively benign and may imitate a benign fibroadenoma in a third of cases [2]. The most common macroscopic finding is the neoplasm well circumscribed, which joins the appearance found in the present case.

In almost every case in the literature, the diagnosis of primary osteocarcoma was established histologically [6]. Histologically, this tumor is indistinguishable from the conventional osteosarcomas of the bone or other extraskeletal ones [3]. The diagnosis criteria of primary breast osteosarcoma include the absence of a tumor bone, the presence of the osteoid substance or bony streaks and the lack of an associated epithelial tumor component [2]. The absence of the epithelial component must be confirmed by immunohistochemical study or by ultrastructural study [7]. In our patient, the diagnosis of primary osteosarcomas of the breast was established on the morphology by the absence of an epithelial component and confirmed by negative staining with cytokeratin antibody (AE1/AE3). The principal histological differential diagnosis in our case was metaplastic carcinoma [1]. However, this was excluded because of negative epithelial markers on immunohistochemical staining.

Malignant phyllodes with osteosarcomatous differentiation can be also raised as the differential diagnosis. The treatment is surgical by a complete removal of the tumor with negative margins or a mastectomy. An axillary lymph node dissection is essentially not indicated because an axillary node involvement is exceptional [8].

In the present case, axillary lymph node dissection was not performed.

The role of adjuvant therapy is unclear because of limited data and his efficacy has not been well established [9].

Primary osteosarcomas of the breast have a poor prognosis with a high possibility of recurrence and metastasis, especially by hematogenous route instead of lymphatic spread. The most common distant site for metastasis are the lungs [2]. Silver et al. in their study of 50 patients with primary breast osteosarcoma reported a 5-year survival of 38%, with 28% of patients developing local recurrence and 41% with distant metastases [2].

It is essential to be aware of this unusual pathologic tumor variant and to differentiate it from metaplastic carcinoma. An early diagnosis, confirmed by an immunohistochemical study and a rapid treatment mainly surgical, is necessary to improve the prognosis, which remains very poor despite everything.