Diagnosis and Management of Large Extraosseous Myxoid Chondrosarcoma of the Buttocks: A Case Report

Abstract

Patient: Male, 65-year-old

Final Diagnosis: Extraskeletal chondrosarcoma

Symptoms: Huge buttock tumor • tumor rupture

Clinical Procedure: —

Specialty: Surgery

Objective: Rare coexistence of disease or pathology

Background

Extraskeletal chondrosarcoma is a rare soft tissue sarcoma with no characteristic imaging and clinical manifestations. Therefore, early preoperative diagnosis is difficult and ultimately depends on postoperative pathology and genetic diagnosis.

Case Report

A 67-year-old man presented with a huge buttock tumor. The maximum transverse section length of the tumor was 40 cm. Due to the large size and long duration of the tumor, the tumor ruptured and invaded part of the sacrum. The preoperative diagnosis was not clear, the tumor was completely removed by surgery, and the wound was repaired. Adjuvant radiotherapy was given after surgery, and the prognosis was good.

Conclusions

This case report demonstrates the importance of radical surgical resection and postoperative adjuvant chemotherapy for the prognosis of extraosseous chondrosarcoma. It also suggests that sometimes the early diagnosis of this type of tumor is difficult, depending on postoperative pathology and genetic diagnosis.

Introduction

Extraosseous (soft tissue) chondrosarcoma is a rare type of soft tissue sarcoma, accounting for 2.5% to 3% of all soft tissue sarcomas [1]. Extraosseous chondrosarcoma has been reported in most organs, but it mainly occurs in the proximal and deep soft tissues of the extremities. Imaging examination lacks characteristics and relies on pathological examination. Radical surgical resection combined with radiotherapy or chemotherapy is still the main treatment for extraosseous chondrosarcoma. The long-term survival rate of extraosseous chondrosarcoma is relatively high, and the high local recurrence rate and new distant metastasis in some cases are the characteristics of the disease. In this case, we report a giant extraskeletal chondrosarcoma of the hip with a history of up to 6 years and a maximum cross-sectional length of 40 cm. At the time of diagnosis, the tumor had ruptured and invaded part of the sacrum. Such a huge extraskeletal chondrosarcoma had never been reported in the previous literature. Finally, good prognosis was achieved through surgery and postoperative chemotherapy.

Case Report

A 67-year-old man was admitted to the hospital with concerns of a subcutaneous mass on his right buttock, which had gradually increased in size over 6 years and was accompanied by redness, swelling, and ulceration over the previous 2 weeks. The patient reported first palpating a peanut-sized subcutaneous mass that was non-tender on his right buttock 6 years earlier. Over time, the mass gradually grew, but the patient did not seek medical attention. Two weeks before presentation, he noticed redness and ulceration, and despite treatment with anti-infectives and wound care, there was no improvement. He denied any history of chronic diseases, such as hypertension or diabetes, and there was no family history of cancer or related conditions. Physical examination revealed a subcutaneous mass on the right buttock, measuring approximately 45×35 cm at its base, with a height of about 15 cm. The upper boundary was aligned with the third lumbar vertebra, the lower boundary extended to the middle and upper third of the thigh, the lateral boundary corresponded to the anterior superior iliac spine, and the medial boundary extended about 10 cm beyond the midline. The central rupture measured approximately 20×15 cm, with a detectable subcutaneous sinus cavity. The exudate was yellow-white with a foul odor, and there was marked swelling around the wound (Figure 1A, 1B). Puncture biopsy identified a large number of amorphous mucus samples; a small number of spindle cells and histiocytes were observed under the microscope. It was considered to be a spindle cell soft tissue tumor with a large amount of mucus formation.

Figure 1.

(A, B) Front and side views of the lesion showing a central ulceration. (C) Complete excision of the specimen tissue. (D) The tumor wound was repaired.

Further auxiliary examination revealed a white blood cell count of 9.1×10 /L, with a neutrophil percentage of 83.8% and a lymphocyte percentage of 9.1%. Hemoglobin concentration was 85 g/L, and serum creatinine concentration was 73.3 μmol/L. Alpha-fetoprotein was 1.5 ng/mL, carcinoembryonic antigen was 1.0 ng/mL, carbohydrate antigen 199 was 7.1 U/mL, carbohydrate antigen 125 was 2.2 U/mL, and carbohydrate antigen 242 was 2.9 IU/mL. A plain computed tomography (CT) scan revealed a large mass with slightly low- to mixed-density areas, calcifications, and gas shadows in the subcutaneous soft tissue of the right buttock and sacrococcygeal region, with local involvement of the sacrum. No effusion or enlarged lymph nodes were observed in the pelvic cavity, and no significant abnormalities were found in the brain, lungs, or abdomen (Figure 2A). Magnetic resonance imaging (MRI) with enhancement revealed a large soft tissue mass on the right buttock and sacrococcygeal region with long T1 and T2 signal shadows and uneven signals. Multiple segmented shadows and the presence of air subcutaneously were noted, but the boundary of the lesion was clear. After contrast enhancement, there was obvious uneven enhancement, showing a honeycomb pattern with multiple non-enhanced areas in the center of the lesion. Bone destruction in the adjacent right sacrum showed long T1 and long T2 signal shadows, with heterogeneous enhancement following contrast (Figure 2B–2D). In addition, we performed a biopsy of the tumor. The results showed that a large number of amorphous mucus samples and a small number of spindle cells and tissue cells were observed under the microscope. It was considered to be a spindle cell soft tissue tumor with a large amount of mucus formation.

Figure 2.

(A) Computed tomography images showed slightly low/low mixed-density shadows, calcification shadows, and local sacral involvement. (B–D) Magnetic resonance images showed long T1 and long T2 signal shadows with uneven signals, and multiple segmented shadows were found in them. The bone destruction of the right part of the adjacent sacrum showed long T1 and long T2 signal shadow, and heterogeneous enhancement could be seen after enhancement.

The patient was thus scheduled for surgical intervention. Before the operation, the incision was designed according to the boundary of the tumor, and the skin flap was reserved to repair the wound. There was no capsule formation in the tumor, but there was a clear tissue boundary between the tumor tissue and the normal tissue. According to the surgical principle of soft tissue sarcoma, the surgical area was 3 to 4 cm outside the boundary, and stripping was done along the loose tissue layer outside the tumor during the operation. The tumor was rich in blood supply, and electrocoagulation and ligation were performed during separation. Part of the tumor tissue adhered to the gluteus maximus, and extended resection was performed together with part of the gluteus maximus. The tumor tissue was closely adhered to the right part of the sacrum, and the bone was eroded, combined with preoperative imaging data. A wire saw was used to excise the affected bone, and the tumor was removed entirely. The surgical site was thoroughly irrigated with sterile water, and the wound was reconstructed using fascial tissue flaps (Figure 1C, 1D).

The postoperative pathological examination revealed that the tumor measured approximately 40×31×14 cm, with no capsule but a defined boundary. The cut section of the tumor appeared translucent, containing a large amount of mucus, with some areas having a jelly-like consistency. Light microscopy showed a lobulated tumor structure consisting of neoplastic chondrocytes embedded in a cartilage matrix. Chondrocytes were densely packed at the periphery of the lobules and sparse in the center, where the matrix tended to calcify. Tumor cells were round, triangular, or star-shaped, located within lacunae, and were numerous with variable nuclear sizes, including some with double nuclei. The cartilage matrix was abundant, with areas of calcification, and bone invasion was observed. Immunohistochemical analysis showed the following results: CD56 (−), cytokeratin (CK) (−), Ki-67 (5%+), P53 (+), S-100 (+), SATB-2 (+), vimentin (+), c-Myc (−). The final diagnosis was extraosseous chondrosarcoma (common type, grade II), predominantly grade I, with some areas of grade II (Figure 3A–3D).

Figure 3.

(A) Chondrocytes were nodular growth (hematoxylin and eosin [H&E] ×40). (B) Chondrocytes were abundant, oval, with different sizes of nuclei, double nuclei, chromatin concentration, and moderate cytoplasm (H&E×100). (C) Invasive growth of tumor tissue interspersed between trabecular bone (H&E×100). (D) High magnification showed that chondrocytes were obese, the nucleus was enlarged and irregular, and calcification could be seen (H&E×400).

Routine symptomatic treatment was given after surgery, and the incision in the surgical area healed well when the sutures were removed (Figure 4A). After wound healing, considering the patient’s general condition and pathological results, the original surgical area received a complete course of radiotherapy. After complete treatment and rehabilitation, the patient could lie flat in a normal supine position and walk normally, which greatly improved the quality of life. During the 5-year follow-up, there was no recurrence and metastasis of the tumor in the surgical area (Figure 4B).

Figure 4.

(A) The incision was well aligned when the sutures were removed. (B) The patient at the 5-year follow-up after surgery.

Discussion

According to the WHO (2020) classification of bone tumors [2,3], chondrosarcoma can be categorized based on its location into intramedullary chondrosarcoma, bone surface chondrosarcoma, periosteal chondrosarcoma, and extraosseous (soft tissue) chondrosarcoma. The pathological subtypes include common type, dedifferentiated, mesenchymal, and mucinous variants. Based on the degree of differentiation, chondrosarcomas are classified as grade I, grade II, or grade III. Chondrosarcoma has been reported in various organs but predominantly occurs in the proximal and deep soft tissues of the extremities, such as the thighs, pelvis, lower limbs, and lungs. The clinical presentation is often nonspecific, with initial symptoms typically including tenderness and a palpable mass. Other symptoms are usually related to compression or invasion of adjacent tissues [4]. The tumor, in this case, was located in the soft tissues of the buttocks and initially presented as a palpable subcutaneous mass. As the mass grew, the patient experienced tenderness and difficulty lying in the supine position. Eventually, redness, swelling, and ulceration developed due to excessive skin tension. The mass did not invade or compress the nerves; therefore, the patient did not experience symptoms such as lower limb numbness or difficulty walking. In retrospective studies, the typical age of onset for extraosseous chondrosarcoma is between 30 and 60 years, with men being more frequently affected than women, at a ratio of 2: 1. There was no significant correlation between the patient’s sex or age group and the tumor’s location [4,5]. A search on PUBMED using the terms “buttocks” and “extraosseous chondrosarcoma” revealed that only 6 such cases have been reported in the literature. The largest tumor reported had a cross-sectional length of 17 cm [6–11]. In the present case, the tumor had been progressing for at least 6 years, with a maximum cross-sectional length of 40 cm, making it the largest reported to date.

CT imaging of extraosseous chondrosarcoma typically lacks specific features and most often presents as a heterogeneous soft tissue tumor with areas of lower density and punctate calcifications, accompanied by mild or no enhancement. MRI scans can show high-tension signals with internal low-tension septal lesions, often revealing a distinct lobulated structure [12]. In the present case, the imaging findings were consistent with extraosseous chondrosarcoma, displaying soft tissue shadows with calcification, septation, lesion edge enhancement, and lobulated changes. Retrospective analysis suggests that PET/CT is highly accurate for diagnosing chondrosarcoma and detecting metastases, aiding in clinical decision-making [13], although its high cost limits widespread use. The definitive diagnosis of extraosseous chondrosarcoma primarily relies on pathology, immunohistochemical staining, and genetic testing. The typical pathological hallmark is a biphasic differentiation pattern made up of undifferentiated round and spindle cell components, along with islands of hyaline cartilage. The primary feature of immunohistochemical staining in extraosseous chondrosarcoma is the positive expression of S-100 in the cartilage areas, along with high expression of vimentin and CD99 in the undifferentiated tumor cell regions, while epithelial markers such as CK and epithelial membrane antigen are not expressed [14]. In the present case, immunohistochemical staining revealed positive results for S-100, P53, SATB-2, and vimentin, while CD56, CK, and c-Myc were negative. The Ki-67 expression level in tumor cells was approximately 5%, aligning with existing literature. At the molecular genetics level, extraosseous chondrosarcoma is characterized by translocations involving the NR4A3 gene, with 5 known fusion genes: EWSR1 (22q12.2), TAF15 (17q12), FUS (16p11.2), TCF12 (15q21), and TFG (3q12.2), with EWSR1 and TAF15 being the most common. Notably, TAF15:: NR4A3 fusion has been significantly correlated with tumor diameters greater than 10 cm [15]. Chromogenic in situ hybridization of CHRNA6 RNA is a potentially valuable auxiliary histological tool for diagnosis [16]. However, due to cost constraints, genetic testing was not performed in this case. Extraosseous chondrosarcoma must be differentiated from chordoma, myoepithelial tumors, and poorly differentiated sarcomas. In our patient, the destruction of the right sacrum raised questions about whether the tumor originated from the sacrum or whether the bone destruction was a result of tumor invasion, which was clarified through pathological assessment.

Radical surgical resection remains the primary treatment for extraosseous chondrosarcoma. As a soft tissue tumor, extraosseous chondrosarcoma typically exhibits a defined boundary with surrounding tissues. To ensure negative margins, surgical procedures often involve either expanded resection or complete removal of the affected organ tissue. The patient, in this case, presented with primary chondrosarcoma of the buttock, characterized by a prominent elevation on the body surface. Due to the prolonged duration of tumor growth, the patient exhibited ulceration and signs of infection at the time of treatment, along with invasion into the sacrum. The tumor was completely excised, and the wound was reconstructed using fascial tissue flaps. Previous literature indicates that most patients with lymph node metastasis present with high-grade tumors, underscoring the importance of sentinel lymph node biopsy or even dissection in cases involving lymph node metastasis [17]. The effectiveness of postoperative chemoradiotherapy remains controversial. Some researchers have found that patients who underwent surgery combined with radiotherapy experienced better local recurrence rates and survival outcomes than did those who did not receive radiotherapy [18,19]. A multivariate evaluation study found that neither chemotherapy nor radiotherapy significantly improved survival rates in this patient population. Most extraskeletal chondrosarcomas are believed to be resistant to chemotherapy, with resistance mechanisms potentially including low mitotic activity and a dense extracellular matrix, which limit drug permeability to the tumor microenvironment [14,18,20]. Nonetheless, patients with unresectable tumors and those exhibiting signs of metastasis or recurrence after tumor resection still require systematic radiotherapy and chemotherapy. In addition to cytotoxic drugs, anti-angiogenic agents present promising alternatives. Specifically, the tyrosine kinase inhibitors sunitinib malate and pazopanib demonstrate clinical value in patients with progressive and advanced tumors, particularly for those who have experienced failure of first-line chemotherapy with anthracycline drugs [20]. Considering the patient’s physical condition, radiotherapy was administered following wound healing.

Multiple Cox regression analysis has identified [4,21,22] several poor prognostic factors for extraskeletal chondrosarcoma, including high histological grade, older age, larger tumor size, and lack of extensive resection. Due to the relatively small number of patients with extraskeletal chondrosarcoma, large-scale retrospective studies on survival rates are limited. The most recent substantial retrospective series indicates that the 5-year, 10-year, and 15-year survival rates are 82% to 90%, 65% to 70%, and 58% to 60%, respectively [23]. Although the long-term survival rate for extraskeletal chondrosarcoma is relatively high, compared with that of many other soft tissue sarcomas, the disease is also characterized by a high local recurrence rate. Notably, reports suggest that more than 80% of cases will develop new distant metastasis despite complete surgical resection [5]. While the survival duration of patients with metastatic tumors tends to be shorter, extraskeletal chondrosarcoma is considered an indolent tumor, allowing most patients to experience prolonged survival even in the presence of metastatic disease. Of note, patients with EWS-NR4A3 translocation demonstrate lower rates of distant metastasis and higher survival rates than do those with TAF15-NR4A3 translocation [18]. Furthermore, studies have indicated that immunohistochemical expression of P53 and a Ki-67 proliferation index of 10% or higher can correlate with poor clinical outcomes, such as increased recurrence and metastasis rates [24]. In the present case, despite the long disease duration and significant tumor size, there were no indications of lymph node involvement or distant metastasis. We surmise that this may be attributed to the tumor’s histological grades being predominantly grade I and partially grade II. Nevertheless, we have planned regular follow-ups for our patient.

Conclusions

This case report demonstrates the importance of radical surgical resection and postoperative adjuvant chemotherapy for the prognosis of extraosseous chondrosarcoma. It also suggests that sometimes the early diagnosis of this type of tumor is difficult and depends on postoperative pathology and genetic diagnosis.