Table 3 Salient features of primary pulmonary myxoid sarcoma and differential diagnoses

Primary pulmonary myxoid sarcoma (PPMS)

Well-circumscribed, lobulated, reticular network of delicate lace-like cellular strands and cords in abundant myxoid stroma, tumor cells are stellate, polygonal with also chondrocyte-like or physaliferous-like tumor cells first reported in our case, prominent lymphoplasmacytic infiltrates within and at periphery of tumor.

Vimentin+, EMA+, CK--, TTF-1-, S-100-, calponin-, SMA-, desmin-, ALK-, CD31-, CD34-.

EWSR1-CREB1 fusion

NA

Extraskeletal myxoid chondrosarcoma (EMC)

Well-circumscribed, multinodular, tumor lobules separated by fibrous septae, umor cells epithelioid to spindled arranged in cords, strands, or clusters embedded in abundant myxoid stroma.

Vimentin+, S-100+, rarely EMA+, keratins+.

,EWSR1-NR4A3,

TFG-NR4A3,

HSPA8-NR4A3, TCF12-NR4A3,

FUS-NR4A3 or TAF15-NR4A3 gene fusion

S-100+, different molecular genetics. Rare as primary in lungs, may present as lung metastasis.

Angiomatoid fibrous histiocytoma (AFH)

Sheets and islands of spindle to epithelioid cells with bland ovoid vesicular nuclei and abundant eosinophilic cytoplasm within loose myxoid stroma.

ALK+, desmin+.

EWSR1-ATF1, FUS-ATF1 gene fusion

No lobular or reticular architecture, no chondrocyte-like or physaliferous-like cells, ALK+ and desmin+, with different molecular genetics in AFH.

Myoepithelial tumors (MT)

Well-circumscribed, solid sheets, nested or cord-like growth pattern, hyalinized or myxoid stroma, moderate to severe nuclear pleomorphism.

Cytokeratins+, EMA+, S100+, calponin+, SMA+, p63+, GFAP+.

EWSR1-FUS,

EWSR1-PBX1, EWSR1-ZNF444, EWSR1-POU5F1 gene fusions

No reticular pattern, no chondrocyte-like or physaliferous-like cells, different 1HC and molecular genetics in MT.

Pulmonary microcystic fibromyxoma (PMF)

Well-circumscribed, bland spindled to stellate cells widely spaced within prominent fibromyxoid stroma with prominent cystic change.

Vimentin+, CD34-, CD31-, HMB45-, SMA-, desmin-, S-100-, ALK-, CKpan-, EMA-, calretinin-, TTF1-

none

Prominent cystic pattern, much less cellular, no chondrocyte-like or physaliferous-like cells, no diagnostic molecular genetic change and not endobronchially located in PMF.

Inflammatory myofibroblastic tumor (IMT)

Areas of myxoid stroma with prominent vessels or hyalinized collagenous stroma, and contain a prominent infltrate of plasma cells and lymphocytes.

SMA+, desmin+, ALK+, rarely keratins+

RANBP2-ALK, RRBP1-ALK,

ETV6-NTRK3 gene fusions

No reticular pattern, prominent inflammatory component, no chondrocyte-like or physaliferous-like cells, SMA+, ALK+ with different molecular genetics in IMT.

Low grade myxoid liposarcoma (LGML)

Large well-circumscribed, monotonous small ovoid cells with fine chromatin, inconspicuous nucleoli, and scant cytoplasm., many characteristic lipoblasts., prominent plexiform vasculature, myxoid background with areas of mucin pooling, imparting a “pulmonary edema-like” pattern.

S-100+, rarely MDM2+ and CDK4+

DDIT3-FUS and DDIT3-EWSR1 gene fusions

Characteristic prominent plexiform vasculature, “pulmonary edema-like” pattern, S-100+, different molecular genetics in LGML. Lung is rare site for primary LGML.