Follicular dendritic cell sarcoma of the colon mimicking stromal tumour

Aims: Follicular dendritic cell tumours are very rare neoplasms that often occur in lymph nodes. We report here a case in the colon, a hitherto unrepo rted site, in a 37-year-old female. The differentiation from gastrointestin al stromal tumour is emphasized. Methods and results: The tumour was tan, elastic and solid with surface ulc eration. Microscopically, it was composed of oval to spindle tumour cells w ith syncytial cytoplasm arranged in fascicular and whorled patterns. There were many infiltrating lymphocytes. The histological appearance resembled g astrointestinal stromal tumour, thymoma or meningioma, Distinct from the st romal tumour, the lymph node was also involved by the tumour. Immunohistoch emically, the tumour cells were positive for CD21, CD35 and CD68, but negat ive for cytokeratin, CD34, smooth muscle actin, desmin, S100 protein, epith elial membrane antigen, leukocyte common antigen, HMB-45 and c-kit. In-situ hybridization study was negative for Epstein-Barr virus RNA sequences. Ult rastructurally, the tumour cells possessed cytoplasmic processes joined by desmosomes. Conclusions: This entity should be considered in the list of differential d iagnoses for gastrointestinal stromal tumour. The lymph node metastasis and immunohistochemical features are of value for identification of this rare neoplasm,