Mesenchymal Tumours and Lymphoma Flashcards
What are mesenchymal tumors?
Practically, they can be thought of as non-epithelial, non-melanocytic, non-lymphomatous skin tumors.
What are some of the types of mesenchymal tumors of the skin?
- tumors of fat
- tumors of fibrous tissue
- tumors of blood vessels and lymphatics
- tumors of muscle
- tumors with nerve sheath differentiation
What are malignant mesenchymal tumors called?
Sarcomas
Describe benign tumors of fat.
Name: lipomas
Clinically Features:
- age 40+
- associated with obesity
- may be very large
- bright yellow homogenous fat with fine fibrous capsule and trabeculae
- greasy cut surface
Histological features:
- composed of mature adipocytes with uniform nuclei resembling normal white fat
- small amounts of fibrous tissue
What are the variants of lipoma?
These are benign tumors with similar macroscopic appearance but variable microscopic appearance.
- spindle cell lipoma
- chondroid lipoma
- pleomorphic lipoma
- angiolipoma - capillaries more prominent
Describe a malignant fat tumor.
Name: liposarcoma
3 main types:
a) atypical lipotamous tumour/well differentiated liposarcoma
b) myxoid/round cell liposarcoma
c) pleomorphic liposarcoma
Deep soft tissue
What is a dedifferentiated liposarcoma?
A biphasic tumor that includes an undifferentiated sarcomatous component.
What would MDM2 genetic amplification indicate?
Well-differentiated tumors.
What are some of the tumors of fibrous tissue?
a) Dermatofibroma
b) Defmatofibrosarcoma protuberans (DFSP)
c) Atypical Fibroxanthoma (AFX)
Describe Dermatofibroma.
- benign
- common site: legs of women 20-50
- recurrence not common
Histology:
- tumor is composed of fibroblastic and histiocytic cells arranged in sheets or intersecting fascicles
- mixed population of cells – inflammatory cells consisting of lymphocytes, plasma cells and foamy histiocytes are also seen
- the stroma contains delicate collagen fibers in between cells
- mitotic activity not increased
- cytologic atypia absent
- no sharply defined borders
- usually show entrapment of surrounding dermal collagen
- overlying epithelial hyperplasia and hyperpigmentation
Describe DFSP.
- well differentiated primary fibrosarcoma of the skin
- slow growing, can be locally aggressive and recur, but rarely metastasize
- firm, solid nodules mostly found on trunk
Histology:
- composed of fibroblasts arranged radially in a stroriform patter (irregular pattern denoting a straw mat)
- mitoses present
- often show deep extendion into subcutaneous fat
- lace-like pattern
What are the key differences between Dermatofibroma and DFSP?
- the deep margin of DF usually shows limited infiltration into subcut tissues, whereas DFSP has more extensive infiltration.
- DSFP has more homogenous population of tumor cells, lacks inflammatory cells, foamy histiocytes and giant cells
- Stratiform pattern more pronounced in DFSP
- Mitotic activity increased in DFSP
- DF = factor 13a positive
- DFSP = CD34 positive
Describe AFX.
- generally rapidly growing nodular lesions in sun exposed areas of older patients
- rapid growth
- usually polypoid without ulceration.
- 1-6cm
- local excisions usually curative and recurrence is rare
Histology:
- composed of atypical, pleomorphic spindle cells
- storiform or fascicle pattern
- abundant mitoses, but some mitotic figures atypical
- use immunohistochemistry to exclude melanoma, spindled squamous cell carcinoma or leiomyosarcoma. AFX will be negative for S-100, melan A, desmin and cytokeratins.
- overlying epidermis uninvolved
What are some of the tumors of histiocytes?
a) Juvenile Xanthogranuloma (JXG)
b) Fibroepithelial polyp/skin tag/acrochordon
Describe JXG.
- cutaneous histiocytic lesion usually seen in infancy and childhood
- most patients develop lesions by 6 months
- excellent prognosis – most regress spontaneously
- yellow or brown
Histology:
- composed of sheets of histiocytes (eosinophilic cytoplasm) in dermis and extending to the flattened epidermis
- hallmark = touton giant cell
- inflammatory cells found in moderate numbers
