Rare case of dedifferentiated liposarcoma of the pectoralis major muscle found on screening mammography

Abstract

Liposarcoma of the pectoralis major muscle is exceedingly rare, with less than 10 cases reported in the literature. Dedifferentiated liposarcoma of the pectoralis major is rarer still, with only 2 reported cases. It is particularly important to be able to accurately diagnose dedifferentiated liposarcoma, as it has a much poorer prognosis than well-differentiated liposarcoma and requires different treatment regimens. Percutaneous biopsy is shown to not be helpful in identifying dedifferentiation. However, there are imaging clues that the radiologist can use to identify dedifferentiation and guide the treating surgeons and oncologists. In this report, we describe a case of dedifferentiated liposarcoma of the left pectoralis major muscle found on screening mammography of the left breast.

Introduction

Liposarcoma is a malignant adipocytic tumor arising from the primitive mesenchymal tissues. According to the WHO, liposarcoma can be of 5 distinct types; well-differentiated liposarcoma, dedifferentiated liposarcoma, myxoid liposarcoma, pleomorphic liposarcoma and myxoid pleomorphic liposarcoma [1]_. Well differentiated liposarcoma is also known as Atypical Lipomatous Tumor (ALT) [1]_. Dedifferentiated liposarcoma is defined as well-differentiated liposarcoma with transformation, either in the primary tumor or as a recurrence to a sarcoma that is typically nonlipogenic [2]. In other words, dedifferentiated liposarcoma occurs when a well-differentiated liposarcoma loses its fat cell characteristics, which can occur either in the primary tumor itself or when it recurs after treatment.

Dedifferentiated liposarcomas usually occur in the retroperitoneum, extremities, spermatic cord, and rarely in the head and trunk [2]. Liposarcomas involving the pectoralis major muscle are exceedingly rare. There are fewer than 10 published cases of pectoralis major muscle liposarcoma in the literature at the time of this writing [[3], [4], [5], [6], [7], [8], [9], [10], [11]]. Out of these cases, only 2 are of dedifferentiated liposarcoma [5,8].

We report a case of dedifferentiated liposarcoma of the left pectoralis major muscle in a 58-year-old woman.

Case report

A 58-year-old woman self-palpated a left breast mass and was found to have a partially visualized mass in her left breast on screening mammography. The mass was multilobulated with circumscribed margins and demonstrated high density compared to surrounding breast tissue. No calcifications were seen (Fig. 1A and B). There was no plane of demarcation between the mass and the pectoralis major muscle, raising suspicion that the mass originated from the muscle. This lesion was further evaluated by ultrasound which showed a multilobulated and hypoechoic lesion (Fig. 2). No prior mammograms were available for comparison. A percutaneous biopsy was obtained, which showed a myxoid sarcomatoid neoplasm, most consistent with well-differentiated liposarcoma.

Fig. 1.

(A) LMLO screening mammography image showing a partly visualized multilobulated lesion (arrows) with no plane of demarcation from the left pectoralis major muscle. (B) LCC screening mammography image showing a partly visualized multilobulated lesion (arrows).

Fig. 2.

Ultrasound image showing a hypoechoic, multilobulated lesion (arrow).

A CT scan was performed and demonstrated a low-attenuation lesion arising from the left pectoralis major muscle and enlarged left internal mammary lymph nodes (Fig. 3). No other metastatic lesions were seen.

Fig. 3.

Axial post contrast CT image of the left pectoralis major muscle depicts the heterogeneously enhancing mass involving the pectoralis muscle (white arrow). There’s an enlarged left internal mammary lymph node (open arrow).

Breast MRI (Fig. 4) showed a lesion that measured 9.5 × 5.7 × 5.6 cm. The mass was heterogeneous on T1-WI and predominantly T2-hyperintense with low-signal septations. There was no convincing evidence of fat. There were enlarged left internal mammary lymph nodes. Postcontrast images demonstrated a heterogeneously enhancing mass with predominantly peripheral enhancement on arterial images with increasing peripheral enhancement on delayed images. There were asymmetrically enlarged vessels in the left breast.

Fig. 4.

(A) Axial T1-WI from breast MRI shows a heterogeneous left pectoralis major mass (white arrow) and an enlarged left internal mammary lymph node (open arrow). (B) Axial TRIM image from breast MRI shows a T2-hyperintense left pectoralis major mass (white arrow) with internal low-signal septations and an enlarged left internal mammary lymph node (open arrow). (C) Axial arterial phase post-contrast T1-WI with fat suppression from breast MRI shows a heterogeneously enhancing left pectoralis major mass (white arrow) and an enlarged left internal mammary lymph node (open arrow). Note enlarged vessels (black arrows). (D) Axial delayed post-contrast T1-WI with fat suppression from breast MRI shows a heterogeneously enhancing left pectoralis major mass with further peripheral enhancement (white arrow) and an enlarged left internal mammary lymph node (open arrow). Note enlarged vessels (black arrows). (E) MIP image shows the left breast mass (white arrow) and enlarged left breast vessels (black arrow).

An FDG PET/CT scan was performed to evaluate metastatic disease (Fig. 5). This showed a hypermetabolic lesion in the left pectoralis major muscle with areas of more intense uptake medially (SUV_max = 10.3). There were enlarged and mildly FDG-avid left internal mammary lymph nodes (SUV_max = 4.1). No distant metastatic disease was present.

Fig. 5.

(A) MIP image from and FDG-PET demonstrating a left pectoralis major muscle mass (white arrow) and a subtle area of more intense uptake medially (black arrow). There is an FDG-avid left internal mamarry lymph node (open arrow). No distant metastatic disease is seen. (B) Fused axial image from an FDG PET/CT shows an FDG-avid left pectoralis muscle mass (white arrow).with more intense uptake posteriorly and medially (black arrow, SUV_max = 10.3). There is an enlarged and FDG-avid left internal mammary lymph node (open arrow, SUV_max = 4.1).

Biopsy of the left internal mammary lymph nodes was negative. The patient underwent radiation therapy to the left breast followed by left total mastectomy and lymph node dissection (Fig. 6). The final pathology was reported as dedifferentiated liposarcoma arising from the pectoralis major muscle. The inked resection margins demonstrated well differentiated liposarcoma; however, the resection margins were free of dedifferentiated liposarcoma. The dissected lymph nodes did not show evidence of malignancy.

Fig. 6.

Radiograph of the surgically resected specimen depicting the lesion extending to the resection margin at the 10-11 o’clock locations (arrow).

The patient was without evidence of disease on the last follow-up 10 months following surgery and was then lost to follow-up.

Discussion

It is important to understand and accurately identify dedifferentiated liposarcomas as dedifferentiation worsens the prognosis and increases the risk of local and distant recurrence [12]. Dedifferentiation increases the risk of death 6-fold [12]. Treatment options also change with dedifferentiation, underlining the importance of accurate diagnosis of these cases [13].

Differentiated liposarcoma usually occurs in older adults and is slightly more common in men. Dedifferentiation is found to occur in around 10% of well-differentiated liposarcomas. This is even more common in retroperitoneal lesions [2].

Imaging studies are recommended for initial diagnosis and workup of patients with dedifferentiated liposarcoma. Conventional radiographs and CT scans may show the presence of a mass with a fatty and nonfatty components. The mass in this case showed no convincing evidence of internal fat on CT. When monitoring these patients, attention should be paid to the nonfatty component on follow up imaging for signs of recurrence or progression [14]. These masses may also show calcification, which may indicate osteosarcomatous dedifferentiation or remnants of osseous metaplasia in the well-differentiated components [14].

MR imaging may be useful to distinguish dedifferentiated liposarcoma from other types of liposarcomas. Dedifferentiated liposarcoma may have the nonfatty component showing hypointense T1 signal, hyperintense T2 signal and intense enhancement on post contrast imaging [15]. Central necrosis may also indicate dedifferentiation, which can be seen on CT scans as well [16]. PET/CT scans are also useful to identify dedifferentiation with high specificity and sensitivity. Using an SUV_max cutoff of 4 has been shown to be helpful to differentiate between well differentiated and dedifferentiated liposarcoma [13]. Being able to accurately identify the foci of dedifferentiation within a lesion on imaging will also help guide biopsy and result in better biopsy yields [13].

On pathological analysis, well differentiated liposarcoma demonstrates atypical adipocytes and at least focal nuclear atypia within adipocytes and/or stromal cells. Histologic features are characterized by adipocytes with variation in size and shape, thickened fibrous bands containing atypical fibroblastic cells with enlarged hyperchromatic nuclei, and lipoblasts, which may be present, but are not required for diagnosis [17]. Myxoid stromal change may be present and is occasionally prominent and extensive. When prominent, this finding can mimic other types of sarcoma with myxoid features, most notably, myxoid liposarcoma. Histologically, myxoid liposarcoma displays a uniform cytologic appearance with minimal nuclear pleomorphism while well-differentiated liposarcoma with myxoid features shows at least some degree of nuclear variability as well as occasional pleomorphic cells not seen in myxoid liposarcoma. Additionally, myxoid liposaroma harbors FUS or EWSR1-DDIT3 gene fusion while MDM2/CDK4 amplification is characteristic of well-differentiated liposarcoma [18].

Surgical resection is recommended for accurate pathological diagnosis and tumor classification. This is because percutaneous biopsy has been shown to have low sensitivity to diagnose dedifferentiated liposarcomas [19]. This was true in our patient as well with the total mastectomy specimen yielding the final diagnosis of dedifferentiated liposarcoma of the pectoralis major muscle.

Surgical resection is the mainline treatment for dedifferentiated liposarcoma with the goal of obtaining disease-free resection margins [20]. Systemic therapy may also be considered in patients with advanced disease or if their lesion is not operable [21].

Overall survival is low for patients with dedifferentiated liposarcoma with 5-year disease-specific survival of 44% compared to 93% in well-differentiated liposarcoma [20].

Author contributions

B.V., E.M., C.C. and B.A.: writing of manuscript. B.V. and B.A. in procuring images. B.V., E.M. and B.A. in reviewing and editing manuscript.

Data availability

The data is stored securely according to institution guidelines and will be made available upon request.

Patient consent

Informed consent has been obtained.