Immunohistochemistry showed that the tumour was diffusely positive for CD99; focally positive for cyclin-D1, CD10, CD34, BCL2; and negative for cytokeratins, S100, HMB45, SMA, desmin, caldesmon, estrogen receptor (ER), progesterone receptor (PR), neuroendocrine markers, and gastrointestinal stromal tumour (GIST) markers. The gene discussed is CD99; the disease is gastrointestinal stromal tumor.