Molavi - Soft tissue

Question 1

Quick assessment of a soft tissue tumor / sarcoma

Answer 1

1. Is it circumscribed?
2. Does it resemble the background tissue?
3. Are the cells and nuclei monomorphic?
4. What is the mitotic rate?

If it appears benign and is monomorphic, it probably is.

If it appears malignant and is monomorphic, it is probably a translocation tumor.

If it appears malignant and is polymorphous, it is probably a poorly differentiated sarcoma.

Question 2

The #1 thing you need to know about how sarcomas spread

Answer 2

They look VERY well circumscribed.

They grow in an expansile, pushing fashion, sometimes with a pseudocapsule.

Don’t let this fool you! Unlike epithelial tumors, being well circumscribed is NOT reassuring in a soft tissue mass.

Question 3

Two questions to ask about any spindle cell lesion (usually in the form of IHC interrogation)

Answer 3

1. Could this be a sarcomatoid carcinoma?
2. Could this be metastatic melanoma?

Question 4

Nodular fasciitis

Answer 4

Common mimic of sarcomas

Spindly with large nuclei with prominent reactive nucleoli. “Tissue culture” pattern on histology in a myxoid background.

Question 5

In fibroblast-derived tumors, nucleoli are most often. . .

Answer 5

. . . just reactive.

Question 6

Six things you HAVE to know about solitary fibrous tumor

Answer 6

1. Looks fibroblastic, but isn’t
2. Arises from serosal surfaces (most of the time)
3. IHC pattern is unusual: CD34, CD99, and BCL2 positive.
4. Staghorn vessels are often present
5. “Patternless pattern”, aka chaotically arranged cells, is classic.
6. It can ALWAYS be malignant – even low mitoses shouldn’t reassure you against this. It is VERY difficult to predict how it will behave.