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Flashcards in Soft Tissue Tumours Deck (16):
1

Describe in one or two sentences the classification scheme for mesenchymal/soft tissue tumors.

They are classified by the types of tissue that they recapitulate or differentiate to (e.g. fat, fibrous tissue, muscle, vessels, nerves); in each histogenetic category, they can be divided into benign and malignant (sarcoma) forms. Some soft-tissue tumors have no normal tissue counterpart.

2

Describe the typical pattern of spread of sarcomas when they metastasize.

in contrast to carcinomas, sarcomas usually metastasize via hematogenous routes (e.g. to lung and bone).

3

State the type of cell that gives rise to soft tissue tumors.

Soft tissue tumors are believed to develop due to mutations in mesenchymal stem cells distributed throughout the body.

4

State the most common type of genetic abnormality in soft tissue tumors.

Fusion gene most common?

Specific chromosomal abnormalities (usually translocations) have been identified for some tumors, which can be used as diagnostic markers. Some of the chromosomal abnormalities produce fusion genes that encode chimeric transcription factors, leading to transcriptional deregulation. Other genetic abnormalities result in deregulation of kinase signaling.

The majority of soft tissue tumors occur sporadically. However, some tumors are associated with genetic syndromes:

Neurofibromatosis Type 1 (neurofibroma, malignant peripheral nerve sheath tumor)
Gardner syndrome (fibromatosis)
Osler-Weber-Rendu syndrome (telangiectasia)

5

State which factors are of prognostic importance for soft tissue tumors.

-Histologic classification: morphologic analysis is often complimented by immunohistochemical stains and cytogenetic analysis.
-Histologic grade is important for the prognosis for many types of sarcoma.
-Stage of the tumor determines both prognosis as well as chance of successful surgical excision.
-Tumors arising in superficial location (e.g. skin and subcutis) have a better prognosis than deep seated tumors. Size can also be a prognostic factor: in patients with deep-seated, high grade sarcomas, metastatic disease develops in 80% of those with a tumor larger than 20 cm and 30% of those with a tumor larger than 5 cm. Overall 10-year survival rate for sarcomas is approximately 40%.

6

State which imaging modality is most helpful in the assessment of soft tissue tumors of the extremities.

Imaging studies (such as MRI) are often used in the assessment of soft-tissue tumors; needle biopsy or excisional biopsy is often used to obtain diagnosis and plan therapy.

7

Describe, in no more than a few sentences, the key differences between NF1 and NF2.

a

8

key pathologic findings, such as differentiation, typical locations where they occur, disease associations (if any), and biologic behavior (i.e. metastatic potential, locally aggressive or not)
of
LIPOMAS

Most common soft tissue tumor of adults (rare to see lipoma in the first two decades of life); various subtypes:

Conventional lipoma: most common type, mature fat only
Angiolipoma: mature fat plus small vessel proliferation; can be painful
Spindle cell lipoma/Pleomorphic lipoma: mature fat plus spindle cells/pleomorphic cells
Myolipoma: mature fat plus smooth muscle
Chondroid lipoma: mature fat plus cartilage-like cells
Angiomyolipoma: mature fat plus vessels plus smooth muscle (typically associated with the kidney, and 1/3 occur in patients with tuberous sclerosis)
Myelolipoma: mature fat plus bone marrow elements (usually adrenal gland)

The first three lipoma types listed above typically occur in a superficial location and are well circumscribed and encapsulated. Some of these benign lipomas are associated with chromosome abnormalities. Treatment is by simple surgical excision.

Intramuscular lipoma: infiltrating lipoma involving skeletal muscle

Lipoblastoma/Lipoblastomatosis: refer to circumscribed (lipoblastoma) and diffuse (lipoblastomatosis) forms of fatty proliferation, usually occurring in infants

Patients on long term corticosteroid therapy can get overgrowth of mature adipose tissue in the face (moon face) and on the back (buffalo hump), called “steroid lipomatosis”

9

key pathologic findings, such as differentiation, typical locations where they occur, disease associations (if any), and biologic behavior (i.e. metastatic potential, locally aggressive or not).
of
LIPOSARCOMA

Liposarcoma is one of the most common sarcomas of adulthood and typically occurs in middle to older age adults; this tumor usually arises in the deep soft tissues of the proximal extremities and retroperitoneum.

Morphologic variants include:
Well-differentiated liposarcoma (relatively indolent, local recurrence, but can be fatal when located in the retroperitoneum); when this tumor occurs in a location amenable to surgical excision (such as an extremity or on the trunk) it may be called an “atypical lipomatous tumor”
Myxoid/round cell liposarcoma (intermediate malignancy)
Pleomorphic liposarcoma (aggressive tumor, frequently metastasizes)

Lipomatous differentiation may be difficult to see in the higher grade tumors (look for lipoblasts)

10

FIBROUS TUMORS AND TUMOR-LIKE LESIONS

Reactive pseudosarcomatous proliferations are non-neoplastic, benign lesions that develop following local trauma/injury or are idiopathic. Clinically, they are worrisome as they grow rapidly and can have an infiltrative appearance.

11

Nodular Fasciitis

Usually occurs on the upper extremities, especially the volar aspect of the forearm, followed by the trunk. Although it can occur at any age, patients are usually young adults that present with a several week history of a solitary, rapidly growing, sometimes painful mass; history of previous trauma is present in 10-15%. The lesion is present in the dermis, subcutis, or muscle, and consists of a nodular, yet poorly marginated, cellular proliferation of immature fibroblasts and myofibroblasts in a myxoid stroma. Mitotic figures are numerous, and to the unwary pathologist the lesion can be confused with a true sarcoma. Following excision, the lesion rarely recurs.

12

Myositis Ossificans

This reactive proliferative lesion usually develops in athletic adolescents and young adults and follows an episode of trauma in more than 50% of cases. The lesion is typically found in the muscles of the proximal extremities, and is often 3-6 cm in size. Initially, the lesion is cellular and consists of plump fibroblasts and myofibroblasts as seen in nodular fasciitis. Overtime, the outer margin of the lesion develops osteoblasts, which then deposit mineralized bone in the outermost layer (ossification). Eventually the lesion can become completely ossified. In the proliferative stage, the lesion can be confused with an extraskeletal osteosarcoma.

13

Superficial Fibromatoses:

benign fibroblastic proliferation involving the fascia or aponeuroses (broad tendons); lesions are characterized by nodular or poorly defined broad fascicles of fibroblasts and myofibrobasts surrounded by abundant dense collagen. Many types exist, defined by location, but the most common ones are listed below:

Palmar fibromatosis (Dupuytren’s contracture): after span of years, the palmar fibrous proliferation can cause skin puckering and progressive flexure contracture.

Plantar fibromatosis: similar process involving the plantar aspect of the foot.

Penile fibromatosis (Peyronie disease): similar process involving the penis.

Local recurrence is possible following surgical excision, but these lesions never metastasize.

14

Deep-Seated Fibromatosis (Desmoid Tumors)

These tumors consist of an infiltrative, poorly marginated proliferation of bland fibroblasts with collagen. While these lesions do not metastasize, they will recur if incompletely excised. They may occur at any age but are most frequent in the teens to 30’s, and some are associated with a history of previous trauma. The three main types are described below:

Abdominal Fibromatosis: typically occurs in the musculoaponeurotic structures of the anterior abdominal wall in women during or after pregnancy.

Extra-abdominal Fibromatosis: occurs in men and women with equal frequency and arises principally in the musculature of the shoulder, chest wall, back, and thigh.

Intra-abdominal Fibromatosis: typically occurs in the mesentery or pelvic side walls, often in individuals having familial adenomatosis polyposis (Gardner syndrome).

Virtually all of the above deep-seated fibromatoses have somatic Beta-catenin or adenomatous polyposis coli (APC) gene mutations.

15

FIBROSARCOMA

Fibrosarcomas are malignant, sarcomatous tumors of fibroblasts. These tumors can occur anywhere in the body, but are most common in the deep soft tissues of the extremities. Fibrosarcomas are aggressive malignancies, recurring in more than 50% of cases and metastasizing in more than 25%

16

FIBROHISTIOCYTIC TUMORS

So-called fibrohistiocytic tumors contain cellular elements that resemble both fibroblasts and histiocytes (tissue macrophages). As the phenotype of the neoplastic cells most closely resemble fibroblasts, the term fibrohistiocytic should be regarded as a descriptive term, not one indicating the cell of origin.

Benign fibrous histiocytoma (dermatofibroma) of the skin has been previously discussed, as well as dermatofibrosarcoma protuberans (intermediate malignancy, prone to local recurrences).

Malignant fibrous histiocytoma (MFH) was once considered the most common sarcoma in adults, and refers to a group of sarcomas characterized by cytologic pleomorphism, bizarre multinucleated cells, and storiform architecture. As the phenotype of the neoplastic cell is often recognized as fibroblastic, this group of tumors is being reclassified into other entities, such as myxofibrosarcoma and undifferentiated pleomorphic sarcoma.