An atypical sarcoma of the breast

A 63-year-old female presented with a palpable and painless lump in the axillary tail of her right breast in the last few months. Patient had no personal or familiar background of breast cancer.

The right breast mammogram demonstrated a dense oval mass with circumscribed margins and radiolucent halo around it located in the axillary tail of the breast, measuring approximately 2.3 cm. A slight irregularity in the upper part of the mass is also present. Other findings: benign coil-marked nodule in the upper quadrant junction of the right breast.

The ultrasound study displays a complex cystic lesion with a solid component that has horizontal orientation and well-defined margins, with prominent and centripetal vascularization on power Doppler.

On MRI, the mass was hyperintense in T2WI and hypointense in T1WI. Contrast-enhanced subtraction images demonstrated homogeneous enhancement with a type 2 dynamic curve, and diffusion restriction was observed on b800 diffusion-weighted images with ADC maps.

PET-TC imaging showed low metabolic uptake of the lesion (SUV max 1.52).

An US-guided core needle biopsy was performed, and the sample was analysed by FISH histology for SYT gene rearrangements at the SS18/SYT gene locus (18q11.2), which was positive.

Background

Synovial sarcoma tends to develop in the deep soft tissues near limb joints, with the majority arising within a proximity of a joint. Primary synovial sarcoma of the breast is a rare presentation of this tumour, with very few cases described in the literature [1].

Despite its name, it is believed to originate from mesenchymal cells. In this type of sarcoma, two cell populations are distinguished: spindle and epithelial cells. Depending on which one predominates, it can be classified as monophasic, which is composed exclusively of spindle cells, or biphasic, which shows a mixture of epithelioid elements together with a fusocellular component [1–3].

Clinical Perspective

Synovial sarcomas account for 10% of soft tissue, and they tend to arise in young adults. They often present as a slowly growing painless mass, although pain is not infrequent [2,4,5].

Poor prognostic indicators include old age, tumour size (>5 cm), metastases at diagnosis, high-grade histology, mitotic activity, tumoral necrosis and different locations other than extremities [1,3,6].

Imaging Perspective

The imaging characteristics of synovial sarcomas are typically nonspecific, and reported cases demonstrate a range of presentations for this lesion.

On mammography, they usually present as masses; in 30% of cases, dystrophic calcifications at the periphery of the lesion can be seen. In US a predominantly hypoechoic heterogeneous mass is usually seen [2,5]. The presence of intra-lesional flow is usually associated with aggressiveness. CT shows a soft tissue mass of heterogeneous density and post-contrast enhancement [5]. MRI is the modality of choice to classify the tumour locally. The lesion is usually well-defined, isointense to muscle on T1, hyperintense on T2, showing diffusion restriction and prominent enhancement after gadolinium administration [5].

Immunohistochemistry is decisive for the diagnosis of this tumour, with p63 and CK14 being key among other markers. Molecular confirmation of the translocation t(X;18)(p11.2; q11.2) remains the gold standard diagnosis [1–3]. The limited tissue from a core breast biopsy can complicate the diagnosis [2,4].

Outcome

Synovial sarcoma is an aggressive tumour with high incidence of metastasis, most frequently to the lung, regional lymph nodes and bone, although breast synovial sarcomas rarely involve the axillary lymph nodes [1–3].

Management of this tumour includes complete surgical resection of the tumour with clear margins in order to minimise the risk of recurrence. High-risk cases may need the administration of chemo/radiotherapy [1,4,5].

Take Home Message / Teaching Points

Primary synovial sarcoma of the breast is a rare tumour with nonspecific imaging findings that may mimic less aggressive lesions. In our case, the presence of heterogeneous structure and vascularisation on US and high density with slight irregular margins on mammography raised suspicion. MRI proved to be the most valuable imaging diagnostic tool, showing diffusion restriction of the lesion.

All patient data have been completely anonymised throughout the entire manuscript and related files.