Which of the following bone tumors occurs in young age group, arises in medullary cavity, and characteristically shows sheets of small uniform sized round cells and Homer Wright rossets?

Ans. b (Ewing's tumor) (Ref. Robbin's pathology, 7th/pg. 1301; 558).The four main types of rosettes in pathology :1. Homer Wright rosette: typically seen in neuroblastomas, medulloblastomas, and primitive neuroectodermal tumors (PNETs). It consists of a halo of tumor cells surrounding a central region containing neuropil.2. Flexner-Wintersteiner Rosette: characteristic of retinoblastomas. It consists of tumor cells surrounding a central lumen that contains cytoplasmic extensions from the tumor cells.3. True Ependymal Rosette: consists of tumor cells surrounding an empty lumen. Are characteristic of ependymoma, but not seen in all cases.4. Perivascular Pseudorosette: consists of tumor cells collected around a blood vessel. It's called a pseudorosette because the central structure isn't part of the tumor. These rosettes are common in ependymomas, but you also see them in medulloblastoma, PNET, central neurocytomas, and glioblastomas.EWING'S SARCOMA# Incidence: Constitutes ~10 to 15% of all bone sarcomas.# Age: Peak incidence in the second decade of life.# Origin: Arises in the medullary cavity of the bones.# Location:involves the diaphyseal region of long bones (especially femur) & flat bones (especially pelvis).# X-ray: permeative destructive lytic lesion with "onion peel" periosteal reaction with soft tissue mass.# Histopathology:- It is composed of sheets of monotonous, small, round, blue cells and can be confused with lymphoma, embryonal rhabdomyosarcoma, and small-cell carcinoma.- The cells are rich in glycogen (PAS positive cells).6- The presence of "Homer-Wright rosettes" is indicative of neural differentiation.- Most PNETs arise in soft tissues; they include:* Peripheral neuroepithelioma,* Askin's tumor (chest wall), and* Esthesioneuroblastoma.- The presence of p30/32, the product of the mic-2 gene (which maps to the pseudoautosomal region of the X and Y chromosomes) is a cell-surface marker for Ewing's sarcoma (PNETs).- The classic cytogenetic abnormality associated with this disease (and other PNETs) is t(11;22).- CD99 +.# It is very aggressive tumor and considered a systemic disease and mimics acute osteomyelitis.# Common sites of metastases are lung, bones (bone to bone metastases/), and bone marrow.# Rx:# Systemic chemotherapy is the mainstay of therapy, often being used before surgery.# Local treatment for the primary tumor includes surgical resection, usually with limb salvage or radiation.# Ewing's is a curable tumor, even in the presence of obvious metastasis, especially in children <11 years old.Also Know:TranslocationTtimor# (22q11)Chronic myelogenous leukemia# (12;22)(q 13 ;q 12)Malignant melanoma of soft parts (MMSP)# (11;14)(q13;q32)Mantle cell lymphoma# (14; 18)(q32;q21)Follicular lymphoma# (1;22)(q24;q12)Ewing's sarcoma# (1;7)(p34;q35)T cell acute lymphocytic leukemia (ALL)# (8;14)(q24;q32)Burkitt's lymphoma, B cell ALL# (11;22)(pl3;q12)Desmoplastic small round cell tumor (DSRCT)# (2;13)(q35;ql4)Alveolar rhabdomyosarcoma# (1; 13)(p36;q 14)Alveolar rhabdomyosarcoma# (10; 17)(q 11.2;q23)Papillary thyroid carcinomas# (x, 18)Synovial cell sarcoma