Soft Tissue - Myxoid Pattern

Question 1

Myxoid Pattern

Answer 1

• Tumours with loose extracellular matrix material
• Rich in glycosamino-glycans

Coexists with different cellular components:

Spindle cell:
* Myxoma
* Low Grade Fibromyxoid Sarcoma
* Angiomyxoma
* Fibromyxoma
* Myxoid Liposarcoma

Pleomorphic:
* Myxofibrosarcoma

Prominent blood vessels:
* Angiomyxoma
* Myxoid Liposarcoma

Question 2

Intramuscular myxoma

Answer 2

• Rare, benign, gelatinous lesion resembling fetal umbilical cord; often deep within muscle of extremity
• May derive from modified fibroblasts
• Usually adults ages 40 - 70 years
• Slight female predominance

Multiple myxomas associated with:
* Carney complex
* Fibrous dysplasia (Mazabraud syndrome)

Micro:
* Hypocellular, composed of bland cells, no mitotic activity, no lipoblasts, scant blood vessels; may have focal histiocytes
* Slightly more cellular with collagenized capsule at periphery
* May have areas of increased vascularity or be hypercellular
* Slightly basophilic matrix with usually a few spindle cells at high power with oval nuclei
* May have central mucinous cyst
* At periphery, may infiltrate striated muscle and be associated with muscle atrophy

Molecular:
* GNAS1 mutations in 61% of intramuscular myxomas

IHC:
* Spindle cells: vimentin, CD34 (50%)
* Mucoid matrix: Alcian blue, mucicarmine, colloidal iron
* S100 -ve
* Desmin -ve

Question 3

Low grade fibromyxoid sarcoma

Answer 3

• AKA Evans tumour
• Low grade sarcoma with fibrous and myxoid areas, whorled growth pattern, low cellularity, bland fibroblastic cells and curvilinear or arcuate vessels
• Bland sarcoma that can metastasize after years to decades

Micro:
* Low to moderately cellular, bland fusiform or spindled cells with focal to diffuse whirling in heavily collagenized stroma with abrupt transition to myxoid areas
* Few collagenn rosettes are present
* 45% have epithelioid areas
* 40% contain poorly formed but large collagen rosettes
* Often infiltrates adjacent skeletal muscle
* Occasionally has areas of increased cellularity, atypia, necrosis or mitotic activity characteristic of intermediate to high grade sarcoma
* Recurrences may show increased cellularity and mitotic activity

Molecular:
* Characteristically expresses MUC4
* Has a t(7;16)(q32-34;p11) FUS-CREB3L2 fusion

IHC:
* MUC4 highly sensitive (100%) and specific
* CD99 (90%)
* BCL2 (90%)
* EMA
* vimentin (very nonspecific)