Spectrum of Low-Grade Fibrosarcomas: A Comparative Ultrastructural Analysis of Low-Grade Myxofibrosarcoma and Fibromyxoid Sarcoma

Figures & data

Table 1 Clinicopathologic and Ultrastructural Findings in 15 Low-grade Myxofibrosarcomas

Myx FS #	Age/sex	Primary tumor	Clinical followup	Ultrastructural findings
1	69/M	Ankle	NED (35 mo)	RER+++, Lys, Golgi++, fat droplets
2	74/F	Hand	LR (×5) NED (37 mo)	RER+, Vim++, Lys, actin+/−
3	60/F	Arm	LR (×2) Met (36 mo) DOD (51 mo)	RER++/dilated, Vim+, Lys, Golgi++, MCP, fat droplets
4	72/M	Neck	LR (×1) NED	RER+, Lys, LCP
5	27/F	Neck	LR (×1) NED (46 mo)	RER++, Vim+
6	61/M	Shoulder	LR (×5) Met (79 mo) AWD (117 mo)	RER++, Lys, Golgi++,
7	50/F	Thigh	LR (×4) NED (50 mo)	RER++/cystically dilated, Lys, Golgi++, FCP
8	75/M	Thigh	NED	RER+++, Vim+, Lys, Golgi++
9	42/F	Hand	NED (70 mo)	RER++/dilated, Vim++, Lys, Golgi++, FCP, actin+
10	68/F	Buttock	LR (×1) NED (113 mo)	RER+++/dilated, Vim+, Lys, FCP
11	66/F	Chest wall	LR (×1) NED (27 mo)	RER+, Lys, Golgi++
12	81/M	Arm	LR (×1) NED (38 mo)	RER+, Vim+, Golgi++, FCP, actin+/−
13	61/F	Forearm	LR (×1) NED (62 mo)	RER+++/dilated, Vim+, Lys, Golgi++FCP
14	57/F	Arm	LR (×1) NED (46 mo)	RER++/dilated, Lys
15	61/M	Groin	NED (74 mo)	RER++/dilated, Lys, fat droplets

Note. F, female; M, male; LR, local recurrence; Met, metastasis; ST, soft tissue; NED, no evidence of disease; AWD, alive with disease; RER, rough endoplasmic reticulum; Vim, vimentin intermediate filaments; Lys, lysosomes; LCP, long cell processes; FCP, filopodia-type cell processes.+focal;++moderate;+++well developed;+/−ill-developed.

FIG. 1 Microscopic appearance of low-grade myxofibrosarcoma: (A) low power with spindle cells separated by abundant myxoid stroma and showing condensation around curvilinear vessels (×200;MFS6); (B) detail of a pseudo-lipoblast showing multivacuolated cytoplasm, with similar appearance as the extracellular matrix (×400;MFS15).

FIG. 2 Ultrastructure of myxofibrosarcoma: (A) low-power showing fusiform cells separated by myxoid stroma; abundant cytoplasm is filled with numerous dilated RER cisternae (×4, 320;MFS13);(B) 2 “pseudo-lipoblasts”-type cells showing marked distension and cystic dilatation of RER cisternae (×5, 400;MFS7);(C, D) detail of the distended cisternae, which appear either empty or filled with a granular electronuclent material (×7, 929and ×18,720; MFS 15);(E) cytoplasmic detail with abundant RER, prominent Golgi, and lysosomes (×12, 780;MFS1);(F) plump spindle cells with abundant cytoplasm rich in vimentin-type intermediate filaments, RER, and dense mitochondriae. In addition focal subectoplasmic actin condensation and short filopodia-type cell processes are also evident (×7, 920;MFS9).

Table 2 Clinicopathologic and Ultrastructural Findings in 12 cases of Low-grade Fibromyxoid Sarcoma

FMS #	Age/sex	Primary tumor	Clinical follow-up (mo)	EM findings
1	30/M	Foot	LR×2, Met lung (60 mo) AWD 204 mo	Vim+++, RER mildly developed
2	37/M	Thigh	Met ST (21 mo) Met lung (32 mo) AWD 120 mo	Vim+++, RER mildly developed; PV++; collagen attachments; BM-like matrix
3	23/F	L thigh	NED (58 mo)	Vim+++, RER mildly developed, BM-like matrix, intracellular collagen
4	34/F	Forearm	NED (64 mo)	Very long CP, RER moderately developed, PV+
5	25/F	L post neck	LR+lung met (156 mo) NED (252 mo)	Interdigitating, neural-like CP, RER not well developed, PV++, angulate lysosomes, collagen attachments
6	38/F	Axilla/brachial plexus	LR (40 mo) NED (48 mo)	Vim+++, RER mildly developed, PV+
7	31/M	R knee	NED 48 mo	Vim++, RER mildly developed
8	24/M	R hand	LR (117 mo) NED (120 mo)	Very long CP, RER not well developed, very few organelles, collagen+++
9	11/M	R foot	LR (19 mo) NED (36 mo)	Very long CP, RER moderately well developed, PV+++, collagen attachments, BM-like matrix, collagen+++
10	18/M	L flank	NED (6 mo)	Very long CP, RER moderately well developed, PV+, angulate lysosomes, BM-like matrix
11	11/M	L neck	NED (20 mo)	Vim+, RER mildly developed, BM-like matrix
12	59/F	R groin	NED (1 mo)	RER mildly developed, angulate lysosomes

NOTE. R, right; L, left; F, female; M, male; LR, local recurrence; met, metastasis; ST, soft tissue; BM, basement membrane; NED, no evidence of disease; AWD, alive with disease; RER, rough endoplasmic reticulum; Vim, vimentin intermediate filaments; CP, long cell processes; PV, pinocytotic vesicles.+focal;++moderate;+++well-developed.

FIG. 3 Microscopic appearance of low-grade fibromyxoid sarcoma: showing bland uniform spindle cells arranged in a swirling pattern and embedded in an alternating myxoid and fibrosing stroma (×40;FMS9).

FIG. 4 Ultrastructure of fibromyxoid sarcoma: (A, B) low power showing delicate spindle cells with long, narrow and nonbranching cell processes arranged in a loose (×5, 400;FMS4) or collagenized stroma (×5, 400;FMS8);(C) detail of cell processes showing sparse organelles and small pinocytotic vesicles (×18, 720; FMS 4);(D) linear arrangement of numerous pinocytotic vesicles (×30, 420; FMS 9);(E) cytoplasmic detail with moderately developed RER as well as an ovoid fibrillary structure consistent with angulate lysosomes (×25, 200;FMS10);(F) detail of an angulate lysosomes associated with scattered dense deposits (×17, 000; FMS 12);(G) extracellular deposit of amorphous flocculent substance (×37, 800; FMS 9);(H) intracisternal collagen (×30, 000;FMS3).