Lymph node reticulum cell neoplasm with progression into cytokeratin-positive interstitial reticulum cell (CIRC) sarcoma: a case study

Aims: To detail on sequential biopsies the morphological and immunohistochemical features of a case of primary lymph nodal fibroblastic reticulum cell (FBRC) tumour which progressed into a clinically aggressive cytokeratin‐positive interstitial reticulum cell (CIRC) sarcoma. Methods and results: A 70‐year‐old female underwent surgical excision of an enlarged submandibular lymph node. The nodal architecture was effaced by a neoplastic proliferation of medium to large cells, round to oval to spindle in shape, growing in a storiform pattern. The tumour stained for vimentin, CD68, factor XIIIa, α1‐antitrypsin, fascin and actin. Dendritic and endothelial cell markers were negative. A diagnosis of FBRC tumour was made by combining pathological and clinical data. The patient received no therapy but 5 months later the tumour relapsed, exhibiting a deceptively pleomorphic cytology, phenotypic changes (strong cytokeratin positivity), intense p53 expression and aggressive clinical course with fatal outcome. In‐situ hybridization for Epstein–Barr virus was negative. Conclusions: We speculate that the morphological changes and p53 expression of the relapsing neoplasm might reflect tumour cell dedifferentiation, in keeping with the aggressive clinical course. The intense p53 expression suggests that this oncoprotein might also play a role in reticulum cell tumorigenesis.