PMC4132276_01
Clinical presentation of Case #1: Preoperative CT-scan (A) of the tumour in the lower left abdominal wall. Macroscopic presentation of the surgical specimen (B); central parts of the tumour are well delimited ('core'); the path of the primary laparoscopy is visible. The tumour infiltrated the abdominal skeletal muscles but did not extra into the abdominal cavity.
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F1
A CT-scan unmasked a 4.2 x 2.7 x 7 cm hypodense (50HU) solid mass in the painful abdominal region [Figure  1A]. On gross examination the 13 x 10.5 x 6 cm specimen contained a 7 x 3.5 x 3.1 cm tumour with whitish/pale yellow cut surfaces [Figure  1B].
Histopathology of Case #1: The tumour shows patches of higher differentiated atypical lipomatous tissue (A) but mostly displays only poorly differentiated spindle-shaped cells (B). Prominent areas with myofibroblastic morphology were noticed (C) and immunohistochemistry was positive for Desmin (D) and Actin.
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F2
Haematoxylin and eosin (HE) staining showed a neoplasm with high cellularity and mostly spindle-shaped cells arranged in storiform patterns (Figure  2B).
Molecular hallmarks of Case #1: Immunohistochemistry demonstrates co-overexpression of CDK4 (B) and MDM2 (C) in both the poorly and higher differentiated areas (A: HE-staining of corresponding region). Fluorescence in situ hybridisation shows strong amplification of the MDM2 locus as underlying genetic alteration (D; Green: MDM2 probe, Red: Chromosome 12 reference probe). The features are characteristic of dedifferentiated liposarcoma.
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F3
Neoplastic giant cells with nuclear vacuoles were present (Figure  3) and IHC stainings for CDK4 and MDM2 were positive (3B, C).
PMC4132276_02
Histopathology and molecular hallmarks of Case #2: The tumour showed heterogeneous morphology. Most cells were spindle-shaped but giant cells with segmented nuclei were also present. Focally, transitions into higher differentiated lipomatous tissue were noticed (A). Other areas were of osteoblastic/osteosarcomatous (B) and fibrosarcomatous appearance (C). Fluorescence in situ hybridisation of the MDM2 gene revealed highly amplified clusters in the lipomatous (D, left), fibrosarcomatous and the osteosarcomatous regions (D, right).
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F4
HE stainings showed a mesenchymal proliferation with high cellularity and mixed morphology (Figure  4): The cells were mostly of spindle-shaped appearance with high pleomorphy. Transitions into more differentiated fatty tissue were found (Figure  4A) as well as areas with osteoblastic/osteosarcomatous (4B) and fibrosarcomatous appearance (4C).