Soft Tissue

Question 1

Describe for ossifying fibromyxoid tumor:
Histology and IHC
Age, site
DDx

Answer 1

Histo - lobulated or nodular mass in superficial soft tissue w/ thick fibrous pseudocapsule, that has areas of metaplastic bone formation, that may extend along fibrous septa.
uniform, bland cytology, in cords, nests, small sheets in a fibromyxoid stroma
Focally areas similar to SEF
S100+, Desmin+ (40%) some are MUC4 +

M>F, mean age 50 yrs, LE>trunk > head and neck

DDx
SEF,
LGFMS,
Extraskeletal myxoid chondrosarc
Extra skeletal osteosarcoma
epithelioid schwannoma

Question 2

List the primary locations and characteristic genetic alterations and IHC profile for the different variants of rhabdomyosarcoma

Answer 2

Embryonal – Younger age group, less common in extremities, common in GU, head and neck region, bladder, prostate
Loss of heterozygosity of chromosome 11 - myogenin usually weak

Alveolar – slightly older age group, most common in extremities, also in head and neck, and trunk
Diffuse and strong myogenin, Desmin, and MYOD1
Can show NEUROENDOCRINE stains!! and KERATINS!!
Translocations of chromosomes 1 and 13 and 2 and 13 (fox / pax3/7)

Spindle cell – paratesticular region for children, head and neck for adults
Mutations in MYOD1

Sclerosing – extremities
Mutations in MYO D1

Question 3

Describe the histology, IHC, and clinical (age, site) ftrs of sclerosing RMS
Also list important DDx

Answer 3

Adults, most common in extremities

has abundant hyaline stromal material that brings to mind other tumors such as myoepithelial carcinoma, chrondrosarcoma, and osteosarcoma - also can look like SEF

Desmin is usually positive, but it is often focal and may show a peculiar dot-like staining pattern. Myogenin is typically focal or may even be negative; in contrast, MyoD1 is diffuse

Question 4

Define ectomesenchymoma

age, site, histology

Answer 4

is a rhabdomyosacroma with a neural or neuronal element (synonym is gangliorhabdomyosarcoma)

Head and neck, paratesticular tissue, genitalia, pelvis / abdomen

histology is usually an ERMS like area with ganglion cells, ganglioneuroma, or neuroblastomas or MPNST adjacent to it
areas with ARMS and PNET may more rarely occur