Table 1 Differential Diagnosis of Solitary Fibrous Tumor

Solitary Fibrous Tumor [10, 21]

40 to 70

Equal

Pleura

Meninges; CNS & spinal cord

Deep soft tissues of extremities

Abdominal cavity, the pelvis, or the retroperitoneum

Head and neck

Trunk

Patternless spindled to ovoid cells within a variably collagenous stroma, admixed with branching and hyalinized staghorn-shaped (hemangiopericytomatous) blood vessels.

CD34+, STAT6+

fusion of the NAB2 and STAT6 genes

Synovial Sarcoma, Monophasic [14, 21]

Adolescents & young adults (2/3rds < 50 years)

1.2:1

Most often deep soft tissues of extremities or limb girdles, distal extremities (fingers, hand foot), Head and & Neck

Fascicles & sheets of uniform spindle cells. May have a herringbone pattern. HPC like branching vessels are common. Often contain stromal hyalinized or wiry collagen bundles

SYT +, TLE1+, EMA+, CK+,

STAT6-

SYT-SSX1/2

Malignant Peripheral

Nerve Sheath Tumor [21, 66]

20–50

(median 35)

Equal

Trunk and extremities, followed by the head and neck area

Hypercellular & hypocellular fascicles of spindle-shaped cells (marbleized pattern), perivascular accentuation, HPC-like vascular pattern, increase mitoses, geographic necrosis, heterologous differentiation in 15% of cases

S100 + (< 50%), SOX10 + (< 70%)

GFAP+ (20–30%)

H3K27me3 Loss

NF1, CDKN2A/CDKN2B, and PRC2 core components (EED or SUZ12) mutations

Dedifferentiated Liposarcoma [67]

27–81

(mean age 52)

Equal

Retroperitoneum, spermatic cord and (more rarely) mediastinum, head and neck, and trunk.

Fascicles or sheets of atypical spindle cells along with lipogenic component with atypia

MDM2+, CDK4+, p16+, CD34+/−, STAT6−/+

MDM2 & CDK4 amplification

Sarcomatoid Mesothelioma [65]

41–94

(median 70)

22:1

Pleura, Peritoneum

Fascicles or haphazardly distributed atypical spindle cells with increase mitoses. Densely collagenized stroma with hypocellular atypical spindle cells in desmoplastic mesothelioma

CK+, EMA+, D2–40 +, Calretinin+, WT1 +

BAP mutation

Soft Tissue Angiofibroma [68]

Middle age, peak in 60th decade

0.75:1

Usually subcutis of extremities, particularly involving around large joints like knee

Variably myxoid to collagenous stroma, branching capillary network & uniform bland spindle cells with ovoid or tapering nuclei. Perivascular collagenization

EMA −/+,

CD34 −/+

AHRR-NCOA2

Spindle Cell Lipoma [69]

40–60

10:1

Subcutis of posterior neck, upper back & shoulders

Face, scalp, orbit, oral cavity & extremities rarely involved

Short fascicles of bland spindle cells with short stubby nuclei, variable number of adipocytes, and ropy collagen bundles. Fibromyxoid stroma, mast cells

CD34+, ASMA -, Desmin -, S100-

RB1 deletion

Myofibroma [70]

First decade (< 2 years)

Adults

2:1

Equal

Skin & subcutis of extremities, head & neck & trunk.

Infantile cases involve liver, heart, GIT, brain & bone

Distinctive biphasic pattern with nodules comprising of immature spindle cells in center with HPC-like vasculature and whorls of myoid cells at periphery with a basophilic pseudochondroid appearance

ASMA+/−, CD34 −/+, Desmin +

Nil

Myofibroblastoma [71]

50–60

(median 54)

2:1

Most cases involve Inguinal/groin area (vulva/vagina, perineum, and scrotum)

Short fascicles of spindle cells with short stubby nuclei, interspersed broad collagen bands & variable admixture of mature adipocytes

CD34+, Desmin +

ASMA+/−

RB1 deletion

Cellular Angiofibroma [71]

5th decade in women, 7th decade in men

Equal

Vulvovaginal/ inguinoscrotal & paratesticular region

Randomly distributed short, intersecting fascicles of spindle cells containing stubby nuclei. Scattered medium sized hyalinized vessels. Wispy stromal collagen

ER & PR + (50%), CD34+/−, Desmin −/+, ASMA −/+

RB1 deletion

Deep Fibrous Histiocytoma [21]

6–84

(median 37)

Slightly more in male

Extremities followed by head and neck region

Uniformly cellular storiform to short fascicular pattern of plump spindle cells. HPC-like branching vessels, stromal hyalinization

CD34 + (40%), ASMA f+/−, STAT6 -

Nil

Dermatofibrosarcoma

Protuberans [75]

20–40

Slight male

Trunk, proximal extremities, head and neck region, genital area, the breast, and at acral sites

Dermal uniform spindle cells arranged in storiform, whorls & short fascicles. Infiltration of results in “honeycomb” appearance.

CD34+, ASAMA +/−, STAT6 -

COLIA-PDGFB

Cellular Schwannoma [66]

40–60

Equal

Paravertebral, retroperitoneum, pelvis & mediastinum

Predominantly or exclusively composed of Antoni A areas with interlacing fascicles of spindle cells having tapered nuclei. Hyalinized vessels are focally seen

S100+, SOX10+, STAT6-

NF2 mutations