Pleomorphic liposarcoma of the pectoralis major muscle presenting as a breast lump

Clinical History

A 60-year-old female patient presented with a palpable right breast mass of recent appearance. On physical examination, a non-tender, non-mobile, soft and deep mass was observed in the internal upper quadrant of the right breast.

Imaging Findings

Breast ultrasound confirmed the presence of a solid mass in the right internal upper quadrant. The lesion had central hyperechoic areas, was vascularized, and in close relation with the pectoralis major muscle (Fig. 1).

Magnetic resonance imaging (MRI) better demonstrated that the mass was located in the bulk of the pectoralis major muscle and more precisely was on its sternocostal head (Figs. 2-3). The intramuscular mass enhanced heterogeneously and had a small central lipomatous component. These findings were suggestive of intramuscular liposarcoma.

Computer tomography (CT) performed for distant disease staging did not demonstrated metastasis, particularly on the lung. CT also depicted the intramuscular location of the mass and its small macroscopic fat content (Fig. 4).

Core biopsy confirmed the diagnosis of intramuscular liposarcoma and demonstrated that it was of the pleomorphic subtype (Fig. 5).

Surgical resection of the sternocostal head of the right pectoralis major muscle and homolateral partial mastectomy with wide excision margins were performed, followed by radiotherapy.

The pathology of the specimen confirmed the diagnosis of pleomorphic liposarcoma of the pectoralis major muscle and indicated that the surgical margins were tumour-free.

In the last control, performed one year later, the patient was disease-free.

Discussion

The pectoralis major muscle is an important posterior landmark of the breast. Breast carcinoma is the most common malignancy in women and can invade the chest wall musculature and the pectoralis major muscle. In contradistinction, primary malignancy of the pectoralis major muscle is quite rare and therefore patients with this uncommon entity can pose a diagnostic dilemma, particularly from the physical examination and the non cross-sectional imaging point of view.

Liposarcomas are the second most common mesenchymal sarcomas, accounting for approximately 16–18% of all soft-tissue tumours. They remain the most variable and diverse mesenchymal tumours with a wide spectrum of imaging appearances that reflects their histological heterogeneity.

The World Health Organization has categorized soft-tissue liposarcomas into five types grouped according to their clinical impact into an intermediate (locally aggressive) group composed by the well-differentiated liposarcoma and a malignant group that includes the other subtypes (dedifferentiated, myxoid, pleomorphic, and mixed liposarcoma). Imaging differs among the different subtypes and can suggest the correct histology or at least narrow the differential diagnosis.

Pleomorphic liposarcoma is the rarest histological subtype, representing 5–15% of all liposarcomatous lesions. Patients present with relatively slow-growing, asymptomatic masses, more often intramuscular, and located on the lower extremity (56%), the upper extremity (20%), and the retroperitoneum (9%). It is more common after 50 years of age and has a slight male predominance.

Imaging usually reveals a nonspecific well-defined soft-tissue mass, although infiltrative margins may be seen. MRI is the gold standard imaging modality for diagnosis, local staging, and follow-up of liposarcoma, providing accurate tissue characterization and determination of local extent.

Pleomorphic liposarcomas are high-grade sarcomatous lesions and characteristically appear fairly heterogeneous due to intratumoral haemorrhage and cystic degeneration. Intratumoral macroscopic fat is a suggestive finding and typically represents less than 25% of the tumoral mass. Likewise, due to higher anaplasia and higher histological grade, compared with other types of liposarcoma, pleomorphic liposarcoma less frequently contains adipose tissue, which is identified by MRI in 62–75% of cases. Therefore, although imaging can be suggestive, histology is required for definitive diagnosis.

Metastases most frequently involve the lung as for other high-grade sarcomas, CT being the imaging technique used for whole body staging and assessment of distant spread. Factors associated with a relatively poor prognosis are age greater than 60 years, nonextremity location, deep-seated tumour, and tumour size larger than 5 cm.

The report presented adds an ultrasound, MRI, and CT documented case of the extremely rare pleomorphic liposarcoma of the pectoralis major muscle to literature. The imaging findings helpful for distinguishing a breast mass due to this rare primary muscular malignancy from the more common breast carcinoma setting are emphasized.

The awareness of the possibility of pleomorphic liposarcoma of the pectoral major muscle presentation as a breast mass optimizes the imaging work-up and early diagnosis of this uncommon cause of breast lump.

Differential Diagnosis List

Final Diagnosis

Pleomorphic liposarcoma of the pectoralis major muscle

URL:	https://www.eurorad.org/case/8794
DOI:	10.1594/EURORAD/CASE.8794
ISSN:	1563-4086