Undifferentiated Pleomorphic Sarcoma: A Case Report

Abstract

Undifferentiated pleomorphic sarcoma (UPS) is an uncommon and aggressive soft tissue tumor primarily affecting older adults, often presenting as a rapidly enlarging, painless mass in the extremities or other deep-seated locations. This case involves a 55-year-old woman who experienced a rapidly progressive and painful swelling in her right thigh following trauma. Imaging studies identified a large, lobulated tumor in the adductor muscles, close to the femur and pubic ramus, with no bone involvement or evidence of distant metastasis. The patient underwent surgical excision, and histopathological analysis confirmed high-grade UPS, necessitating adjuvant radiotherapy due to narrow surgical margins. Follow-up evaluations, including MRI scans at six months and one year, revealed no signs of disease recurrence. The case underscores the critical role of early detection, multidisciplinary treatment planning, and rigorous postoperative monitoring to improve outcomes and reduce the risk of recurrence in patients with UPS.

Keywords: immunohistochemistry; limb-salvage surgery; mesenchymal tumor; postoperative radiotherapy; thigh mass; undifferentiated pleomorphic sarcoma (ups).

Figure 1. Clinical image of the right thigh showing swelling of size 30 x 20 cm over the medial aspect.

yellow arrow - depicting the lesion

Figure 2. Coronal section of MRI of the right thigh showing the lesion involving the adductor muscles.

yellow arrows - depicting the lesion

Figure 3. Vertical elliptical incision over the swelling.

Figure 4. Tumor bed post excision of specimen.

FA- Femoral artery; FV- Femoral vein; GSV- Great saphenous vein; SN- Sciatic nerve

Figure 5. Gross image of the resected specimen with overlying fat and ellipse of skin.

Figure 6. Histopathological features of tumor cell patterns in undifferentiated pleomorphic sarcoma

(A) Histopathology image showing tumor cells arranged in a fascicular pattern, characterized by intersecting bundles of spindle-shaped cells. The cells display marked pleomorphism, with variable cell sizes and hyperchromatic nuclei, consistent with the features of a high-grade sarcoma. (B) Histopathology image showing small, round, blue tumor cells with hyperchromatic nuclei and scant cytoplasm. This pattern is indicative of a highly cellular tumor, with densely packed cells that appear uniform in size and shape. The histological appearance supports the diagnosis of an aggressive soft tissue sarcoma.

Figure 7. Immunohistochemical characterization of undifferentiated pleomorphic sarcoma

Subimage (A): CD99 Staining. The tumor cells exhibit strong, diffuse cytoplasmic and membranous staining for CD99, demonstrating widespread expression throughout the tumor tissue. This staining supports the diagnosis of undifferentiated pleomorphic sarcoma, as CD99 is frequently linked to mesenchymal origin. Subimage (B): CD68 Staining. Immunohistochemistry for CD68 shows focal positivity in tumor cells, indicating areas of histiocytic differentiation. CD68, a marker of macrophages and histiocytes, aids in identifying the presence of macrophage-like features within the tumor, which is consistent with undifferentiated pleomorphic sarcoma. Subimage (C): Ki-67 Staining. The Ki-67 staining reveals a high proliferation index, with over 50% of tumor cell nuclei showing positive staining. This high level of Ki-67 expression indicates a highly proliferative tumor, confirming the high-grade nature of the undifferentiated pleomorphic sarcoma. Subimage (D): Smooth Muscle Actin (SMA) Staining. Occasional tumor cells demonstrate cytoplasmic positivity for smooth muscle actin (SMA), suggesting regions of smooth muscle differentiation. The presence of SMA-positive cells, although limited, underscores the heterogeneous nature of the tumor and supports the diagnosis.