<s>[INST] context: Ewing's sarcoma or Ewing sarcoma (/'ju:ING/) is a malignant small, round, blue cell tumor. It is a rare disease in which cancer cells are found in the bone or in soft tissue. The most common areas in which it occurs are the pelvis, the femur, the humerus, the ribs and clavicle (collar bone). Since a common genetic locus is responsible for a large percentage of Ewing's sarcoma and primitive neuroectodermal tumors, these are sometimes grouped together in a category known as the Ewing family of tumors. The diseases are, however, considered to be different: peripheral primitive neuroectodermal tumours are generally not associated with bones, while Ewing sarcomas are most commonly related to bone. Ewing's sarcoma occurs most frequently in teenagers and young adults, with a male/female ratio of 1.6 Although usually classified as a bone tumour, Ewing's sarcoma can have characteristics of both mesodermal and ectodermal origin, making it difficult to classify. James Ewing (1866-1943) first described the tumour, establishing that the disease was separate from lymphoma and other types of cancer known at that time.CD99 antigen (Cluster of differentiation 99), also known as MIC2 or single-chain type-1 glycoprotein, is a heavily O-glycosylated transmembrane protein that is encoded by the CD99 gene in humans. The protein has a mass of 32 kD. Unusually for a gene present on the X chromosome, the CD99 gene does not undergo X inactivation, and it was the first such pseudoautosomal gene to be discovered in humans. [/INST] question: MIC-2 is a marker of - | options: A: Ewing 's sarcoma B: Osteosarcoma C: Dermatofibrous protruberans D: Alveolar cell sarcoma | answer: A </s>