IMMUNOHISTOCHEMISTRY, CD 99 (MIC-2)

What this test checks

Detects CD99, highly expressed in Ewing sarcoma and primitive neuroectodermal tumour (PNET) — aggressive cancers of bone and soft tissue predominantly affecting children and young adults. Also expressed in lymphoblastic lymphoma.

Why do people get this test?

Ewing sarcoma requires intensive multimodal chemotherapy. CD99 strong positivity is a key diagnostic feature that, combined with EWSR1 gene rearrangement testing, confirms Ewing sarcoma — enabling specific treatment to begin.

When you should consider this test

• When Ewing sarcoma or PNET is suspected in a bone or soft tissue tumour
• When classifying small round cell tumours in children or young adults
• As part of small round blue cell tumour diagnostic panel

How to prepare

No preparation needed — performed on biopsy or surgical tissue.