Diffuse-Type Tenosynovial Giant Cell Tumour Involving Bone Masquerading as Langerhans Cell Histiocytosis

Abstract

We presented a case of diffuse-type tenosynovial giant cell tumour (DTSGCT) of foot masquerading as Langerhans cell histiocytosis. Preliminary diagnosis by needle biopsy was difficult due to the major involvement of bones and the overshadowing effect of the accompanying Langerhans cells. The complete curettage specimen with relevant immunohistochemistry and molecular tests made the final diagnosis of DTSGCT possible. The biomolecular mechanism for the masquerading phenomenon was explained by CSF1 overexpression in the neoplastic cells attracting migration and proliferation of CSF1R-positive Langerhans cells.

Detection of CSF1 gene derangement in ‘sclerosing mucoepidermoid carcinoma with eosinophilia’ of the parotid gland masquerading as Langerhans cell histiocytosis

“…Our studies were inspired by the findings of CSF1 rearrangement and its overexpression in tenosynovial giant cell tumors (TSGCT), attracting dendritic cells including Langerhans cells (CSF1 receptor+) to migrate into the mesenchymal tumor and proliferate. 10 , 11 Instead of CSF1 gene rearrangement, we detected increased CSF1 (3'end) copy number with deletion of the 5′ end, coupled with increased expression of CSF1 in tumor cells on RNA scope. Over‐expression of CSF1 without documented translocation has also been found in a proportion of TSGCT.…”

“…The present case with the abundant Langerhans cells masquerading as Langerhans cell histiocytosis triggered the search for an underlying mechanism. Our studies were inspired by the findings of CSF1 rearrangement and its overexpression in tenosynovial giant cell tumors (TSGCT), attracting dendritic cells including Langerhans cells (CSF1 receptor+) to migrate into the mesenchymal tumor and proliferate 10,11 . Instead of CSF1 gene rearrangement, we detected increased CSF1 (3'end) copy number with deletion of the 5′ end, coupled with increased expression of CSF1 in tumor cells on RNA scope.…”

Detection of CSF1 gene derangement in ‘sclerosing mucoepidermoid carcinoma with eosinophilia’ of the parotid gland masquerading as Langerhans cell histiocytosis

“…The present case with the abundant Langerhans cells masquerading as Langerhans cell histiocytosis triggered the search for an underlying mechanism. Our studies were inspired by the findings of CSF1 rearrangement and its overexpression in tenosynovial giant cell tumours (TSGCT), attracting dendritic cells including Langerhans cells (CSF1 receptor+) to migrate into the mesenchymal tumour and proliferate 10,11 . Instead of CSF1 gene rearrangement, we detected increased CSF1 (3'end) copy number with deletion of the 5' end, coupled with increased expression of CSF1 in tumour cells on RNA scope.…”