Osteosarcomatous Divergence in Dedifferentiated Liposarcoma Presenting as a Colonic Mass

Abstract

Dedifferentiated liposarcomas most commonly arise in the retroperitoneum, accounting for 10% of liposarcomas. Heterologous differentiation occurs in 5-10% of dedifferentiated liposarcomas; however, divergent osteosarcomatous differentiation is rare. We report a rare case of initial presentation of dedifferentiated liposarcoma with osteosarcomatous component as a colonic mass in a 72-year-old man. The tumor is mainly composed of bony trabeculae with intervening highly atypical cells and adjacent high-grade mesenchymal nonlipogenic tumor, as well as areas of well-differentiated liposarcoma. Immunohistochemical studies showed diffuse positivity for SATB2 in the atypical cells and fluorescence in situ hybridization revealed high-level amplification of MDM2 gene, supporting the diagnosis of well-differentiated and dedifferentiated liposarcoma with heterologous osteosarcomatous differentiation.

Figure 1

Contrast-enhanced CT scan images of right pericolonic mass: (a) axial and (b) coronal images demonstrate large partly exophytic lobulated mass (blue arrow) arising from the mid ascending colon with heterogeneously enhancement, consistent with mineralization or calcifications.

Figure 2

(a) A low power image showing dedifferentiated liposarcoma with osseous differentiation involving the colonic wall (20X). (b) Dedifferentiated liposarcoma with osseous differentiation adjacent to well-differentiated liposarcoma (left) (20X). (c) Dedifferentiated liposarcoma with osseous differentiation and highly atypical cells (40X). (d) Areas of low-grade osteogenic differentiation with well-formed bone trabeculae and intervening spindle cells (40X). The insert shows high power image of the spindle cells with mild atypia (100X).

Figure 3

(a) Cellular high-grade nonlipogenic sarcoma component composed of spindle and pleomorphic tumor cells (100X). (b) Focal transition into a well-differentiated liposarcoma with atypical stromal cells (100X). (c, d) Nonlipogenic sarcoma with osteoid matrix and highly atypical cells, resembling a high-grade osteosarcoma (100X). (e) Immunohistochemical staining for SATB2 is positive in osteoblastic cells and intervening atypical cells. (f) Areas of thick interconnected trabeculae of immature woven bone lacking osteoblastic rimming (40X).