Soft Tissue Pathology Flashcards
Soft Tissues
Non-epithelial extraskeletal tissues except CNS and reticuloendothelial system.
Mesodermal in origin:
Fat, fibrous tissue, smooth and skeletal muscle, blood vessels
and lymphatics
Soft Tissue
Tumors
- Uncommon
- Most are benign (5:1)
- Often present diagnostic difficulties
- Frequently located deep in the extremities and present as a painless mass
- ~ 1,600 deaths/year from soft tissue tumors in USA
- Most are in children and young adults
- 5th leading cause of death from cancer in children
WHO Classification
50 subtypes of sarcoma:
- Adipocytic
- Fibroblastic/myofibroblastic
- Fibrohistiocytic
- Smooth muscle
- Pericytic (perivascular)
- Skeletal muscle
- Vascular
- Chondro-osseous
- Tumours of uncertain differentiation
Biological Potential
-
Benign
- Rarely recur and if so, in a non-destructive fashion
- < 1/50,000 metastasize
- Unpredictable based on histology
- Ex. cutaneous fibrous histiocytoma
-
Intermediate (locally aggressive)
- Often recur
- Infiltrative and locally destructive
- Ex. desmoid fibromatosis
- Very low metastatic potential
-
Intermediate (rarely metastasizing)
- Locally aggressive with < 2% metastases
- Ex. plexiform fibrohistiocytic tumor
-
Malignant
- Locally destructive growth
- Potential for recurrence
- Recurrences may be of higher grade and greater potential for spread
- Significant risk of distant metastasis (20–100%)
- Low grade sarcomas may have only 2–10% rate of metastasis
- Typically spread via blood to lungs
- Does not usually invade lymph nodes
- Ex. myxofibrosarcoma, leiomyosarcoma
Sarcomagenesis
Not clearly understood:
-
Progressive pattern not well established
- Unlike epithelial neoplasms: in situ precursor lesions ⇒ dysplasia ⇒ malignancy
-
Often do not arise from their corresponding mature adult tissue
- Progenitor cell remains unclear
-
Histogenesis or cell of origin replaced by differentiation
- Rhabdomyosarcoma dx by presence of primitive skeletal muscle cells and IHC of muscle markers
- Many tumors arise in sites where skeletal muscle is sparse or absent
- No evidence that liposarcomas either originate from mature fat or represent malignant transformation of lipomas
- Rhabdomyosarcoma dx by presence of primitive skeletal muscle cells and IHC of muscle markers
Histologic Grading
3 grade system
- Mitotic index & tumor necrosis ⇒ most important features
-
Indicates probability of metastasis and overall survival
- High grade tumors usu. more responsive to chemotherapy
- Does NOT predict recurrence (mainly related to surgical margins)
- Only for untreated primary soft tissue sarcomas
- Not applicable for all sarcomas
- E.g. MPNST, angiosarcoma, extraskeletal myxoid chondrosarcoma, alveolar soft part sarcoma, clear cell sarcoma and epithelioid sarcoma

Sarcomas
Clinical Pearls
- Some benign lesions may not be well-delineated
- Often appear well-circumscribed grossly but almost always infiltrate adjacent tissue at the microscopic level
- No true capsule exists
- Any deeply seated soft tissue tumor should be considered malignant until proven otherwise
- Metastasize via bloodstream (hematogenous spread)
- Most have a predilection for a certain anatomic region and age group
- Histomorphologic pattern and cellularity may vary in different areas
Fibrous Tumor-like Conditions
-
Reactive pseudosarcomatous lesions
- Nodular fasciitis
- Myositis ossificans
-
Fibromatoses
-
Superficial fibromatoses
- Palmar (Dupuytren contracture), knuckle pads, plantar, penile (Peyronie disease)
-
Deep fibromatoses (Desmoid tumor)
- Extra-abdominal
- Abdominal (mesenteric)
-
Superficial fibromatoses
Nodular Fasciitis
Overview
Reactive pseudosarcomatous lesion:
- Most common pseudosarcoma
- Adults
- Locations:
- Volar aspect of forearm
- Chest
- Back
- Solitary, rapidly growing (within weeks), sometimes painful mass
- Preceding trauma reported in 10-15% of cases
Nodular Fasciitis
Characteristics
- Plump fibroblasts (myofibroblasts)
-
Myxoid to fibrous background
- Collagenization progresses with time
- Extravasated RBCs and microcysts are common
- Lymphocytes and giant cells often present
- Mitotic rate is high (no atypical mitotic figures)
-
Typical myofibroblastic IHC:
- SMA and calponin ⊕
- Desmin and caldesmon ⊖
- Recent data indicates fusion of non-muscle myosin (MYH9) gene with USP6 oncogene in NF ⇒ suggests that it is a benign self-limiting neoplasm

Myositis Ossificans
Reactive pseudosarcomatous lesion:
- Athletic adolescents and young adults
- 50% of cases report previous trauma
-
Early phase:
- Swollen and painful
- Appearance similar to nodular fasciitis
-
Middle phase (within three weeks):
- Less painful, firmer
- Zonation ⇒ bone trabeculae at periphery and immature fibroblasts in center
-
Late phase:
- Painless, hard, well-circumscribed mass
- Complete bone metaplasia

Fibromatosis
Overview
Fibrous overgrowths of dermal and subcutaneous connective tissue develop tumours called fibromas.
Are usually benign.
Superficial Fibromatoses
- Palmar ⇒ Dupuytren contracture
- Knuckle pads
- Plantar ⇒ Ledderhose disease
- Penile ⇒ Peyronie disease

Deep Fibromatoses (Desmoid Tumors)
Overview
- No metastases
- Infiltrative pattern
- Local destruction
-
Therapy:
- Complete and wide excision
- Recurrence rate 25-80%
- Radiation therapy
- Complete and wide excision

Deep Fibromatoses
Types
Abdominal vs Extra-abdominal

Gardner Syndrome
Associated pathologies include:
- Familial adenomatous polyposis (FAP)
- Osteomas
- Dental anomalies
- Epidermal inclusion cysts
- Colorectal carcinoma
- Desmoid tumor
Turcot Syndrome
Associated pathologies include:
- Familial adenomatous polyposis (FAP)
- Desmoid tumor
- Medulloblastoma
Fibrohistiocytic Tumors
-
Benign
- Benign Fibrohistiocytoma
- Dermatofibroma (DF)
- Sclerosing hemangioma
- Histiocytoma
- Benign Fibrohistiocytoma
-
Malignant
- Dermatofibrosarcoma protruberans (DFSP)
- Malignant fibrohistiocytoma (MFH)
- Storiform
- Pleomorphic
- Myxoid
- Giant cell
- Inflammatory
- Angiomatoid
Dermatofibroma
“Benign Fibrohistiocytoma”
- Dermis and subcutanous tissue
- Slow growing, painless, mobile nodule
- Small (up to 1 cm) and well-circumscribed
- Bland spindle cells with delicate cytoplasm
- Storiform pattern
- Collagen production
- No mitosis, necrosis, atypia

Dermatofibrosarcoma Protuberans
(DFSP)
- Low grade sarcoma
- Young adults
- Dermis and subcutis of trunk and extremities
- Recurrence in 30% of cases
- Metastases are rare (<5%):
- Lung, lymph nodes
- More frequent after multiple recurrences
- Storiform pattern
- Honeycomb pattern of infiltration into surrounding adipose tissue

Fibrosarcoma
- Adults 40-60 y/o
-
Locations:
- Deep soft tissue of lower extremities, upper extremities, trunk, head and neck
- Subcutis if associated with DFSP, cicatrix, burn, or radiation therapy history
- Usu. a dx of exclusion
- Many sarcomas can have FS-like growth patterns
-
Histology:
- Solid growth of hyperchromatic, malignant spindle cells
- Very cellular
- Herringbone pattern

Malignant Fibrohistiocytoma (MFH)
Overview
- Most common sarcoma of adults
-
Location:
- Musculature of proximal extremities
- Retroperitoneum
- Cutaneous variant ⇒ Atypical fibroxanthoma
- Cell of origin is not identified (IT IS NOT HISTIOCYTIC)
- Can represent the pleomorphic variant of many sarcomas
-
Aggressive tumors
- Recurs unless widely excised
- Metastatic rate: 30-50% (except cutaneous)
- Cutaneous form (atypical fibroxanthoma) very rarely disseminates

Malignant Fibrohistiocytoma
Subtypes
Subtype is not significant except for angiomatoid type (indolent)
- Storiform
- Pleomorphic
- Undifferentiated Pleomorphic Sarcoma
- Myxoid
-
Giant cell
- Giant Cell Rich Osteosarcoma
- Giant Cell Tumor (Osteoclastoma) of Soft Tissue
- Leiomyosarcoma with Osteoclastic Giant Cell Reaction
- Giant Cell Rich Anaplastic Carcinoma
- Inflammatory
- Dedifferentiated Liposarcoma with prominent neutrophilic infiltrate
- Angiomatoid (adolescent, young adult; indolent)

Lipomatous Tumors
-
Benign
-
Lipoma
- Spindle cell
- Angiolipoma
- Intramuscular
- Lipomatosis
- Lipoblastoma
-
Lipoma
-
Malignant
- Liposarcoma
Lipoma
Overview
- Most common primary soft tissue tumor of adult
- Well-encapsulated mass of lobulated adipose tissue
- Microscopically shows lobules of mature adipose tissue (adipocytes and thin strings of connective tissue and capillaries)
-
Clinically significant subtypes:
- Spindle-cell
- Angiolipoma
- Intramuscular

Spindle Cell Lipoma
- Middle aged (45-60 y/o) male
- Lipomatous tumor of the back or the posterior neck
- Gross: lobulated adipose tissue
- Microscopic: abundant spindle cells, may be very cellular and show some atypia

Angiolipoma
Painful subcutaneous mass in forearm of young adult
Vascular channels with microthrombi

Intramuscular Lipoma
Lipomatous growth within skeletal muscle fibers
Diagnostic problem to differentiate from liposarcomas involving skeletal muscle

Lipomatosis
Systemic disorder
Painless symmetrical diffuse deposits of fat beneath the skin of the neck, upper trunk, arms and legs
Thought to be genetic but mode of inheritance is uncertain

Lipoblastoma / Lipoblastomatosis
- Children < 3 y/o
- Upper or lower limb
- Males 2x > female
-
Localized form:
-
Lipoblastoma
- Subcutis
-
Lipoblastoma
-
Diffuse form:
-
Lipoblastomatosis
- Subcutis and skeletal muscle
- Recurrences
- Maturation to adult fat
-
Lipoblastomatosis

Liposarcoma
Overview
Malignant fatty tumor
Can occur in fat cells in any part of the body
Most cases occur in the muscles of the limbs or abdomen

Well-differentiated Liposarcoma
- Lipoma-like (lipoma with atypical cells)
- Sclerosing-spindle cell
- Dedifferentiated (WD with areas of Fibrosarcoma and/or MFH)

Dedifferentiated Liposarcoma
- Areas of transformation into Fibrosarcoma or Malignant Fibrohistiocytoma (MFH)
- Occurs more frequently in the retroperitoneum (local aggressiveness)
- Can also happen in the extremities
- Usu. after multiple recurrences
- May then be associated with metastatic disease (lung)

Myxoid Liposarcoma
Gelatinous, lipomatous tumor
-
Low grade
- Lipoblasts
- Chicken-wire vessels
- Myxoid background
-
High grade
- Round cell ⇒ Low grade plus solid areas of round cells with scant cytoplasm)

Pleomorphic Liposarcoma
- High grade sarcoma with high metastatic potential
- Similar to pleomorphic MFH
- Deep soft tissue of limbs and limb girdle
- Very aggressive
- Very poor prognosis

Liposarcoma Subtypes
Table

Striated Muscle Tumors
-
Benign
-
Rhabdomyoma
- Heart (children)
-
Rhabdomyoma
-
Malignant
- Rhabdomyosarcoma
Rhabdomyosarcoma
Overview
- Malignant tumor of skeletal muscle origin
- Most common soft tissue sarcoma of childhood and adolescence (< 20 y/o)
-
Location:
- Head and neck
- Genitourinary tract
- Extremities
-
Aggressive tumors
- 65% of children are cured
- Adults have worse prognosis
-
Treatment:
- Surgery
- Chemotherapy
- Radiation therapy
-
Subtypes:
-
Embryonal
- Botrioid (better prognosis)
- Spindle cell
- Pleomorphic
- Alveolar (worse prognosis)
-
Embryonal
-
Immunohistochemistry:
- Desmin, Myoglobin, Myogenin ⊕
Embryonal Rhabdomyosarcoma
- 66% of all RMS
- < 10 y/o
- Location:
- Nasal cavities, orbit, middle ear, prostate, paratesticular region
-
Botrioid: hollow organs
- Vagina, bladder, nasopharynx, biliary tract

Alveolar Rhabdomyosarcoma
- Adolescence (10-25 y/o) peak
- Deep musculature of extremities
- Small cells with high N/C ratio
- Pseudoalveolar pattern
- Worse prognosis
- Associated with a translocation mutation ⇒ t (2;13) or t (1;13)

Smooth Muscle Tumors
Benign ⇒ Leiomyoma
Malignant ⇒ Leiomyosarcoma
Leiomyoma
Benign smooth muscle tumors
-
Histology:
- Fascicles of spindle cells intersecting at 90°
- Cigar shaped nuclei
- Fibrillary cytoplasm
- No mitoses, atypia, necrosis
-
Immunohistochemistry:
- Desmin, Actin, Vimentin ⊕
-
Location:
-
Skin and subcutaneous tissue (somatic soft tissue)
- Erectores pilorum
- Erector muscle of nipple
- Media of blood vessel
-
Deep soft tissue
- Retroperitoneum
- Omentum
- Mesentery
- Broad ligament
-
Skin and subcutaneous tissue (somatic soft tissue)

Intravenous Leiomyomatosis
(IVL)
Benign smooth muscle tumor of the uterus that grows within the veins but does not invade the surrounding tissue

Leiomyosarcoma
Overview
- Malignant tumor of smooth muscle origin
-
Locations:
- Cutaneous
- Female genital tract
- Deep soft tissue of extremities
- Retroperitoneum
- 10-20% of all sarcomas
- Women > men
- Death by local extension or metastasis (lung)
Leiomyosarcoma
Characteristics
- Short 90° interweaving fascicles
- Atypical cigar-shaped nuclei
- Atypical mitoses
- Fibrillar cytoplasm (trichrome)
- Variants: myxoid, epithelioid
- Immunohistochemistry: Desmin, Actin, Vimentin ⊕

Synovial Sarcoma
- Unclear cell of origin
- Seems to resemble synovium
-
10% of all sarcomas
- 4th most common sarcoma
- Only 10% intra-articular
- 20-40 y/o
-
Locations:
- Lower extremities, deep seated
- Parapharyngeal, abdominal wall
- Metastasis to lung
- Genetic signature: t (x;18) SYT-SSX gene fusion
-
Biphasic
- Spindle and epithelial (glands)
-
Monophasic
- Spindle (Fibrosarcoma-like)
- Epithelial (glands)
