Extranodal follicular dendritic cell sarcoma: a frequently misdiagnosed entity.

Sir,

Follicular dendritic cell (FDC) sarcomas are rare malignancies arising from follicular dendritic cells found in lymph nodes. Diagnosis is based on expression of CD21 and CD35. Extranodal follicular dendritic cell sarcomas are rare with the oral cavity, tonsil, gastrointestinal tract and liver being the sites reported in the literature. There is no consensus on its management since only anecdotal case reports and short case series exist in the literature. We are reporting a case of extranodal follicular dendritic cell sarcoma arising from the mesentery, which was misdiagnosed and treated as gastrointestinal stromal tumor (GIST).

A twenty-two year old male presented with pain in abdomen of 6 months duration. CECT abdomen revealed a mesenteric mass. The mass was excised and final histopathology was read as high-risk GIST. Hence, he was given adjuvant therapy with oral Imatinib for 2 years. Then he developed local recurrence. Since it was closely abutting the ileocolic artery, right hemicolectomy was performed. The patient was referred to our center for an opinion regarding further management. On presentation, the patient was largely asymptomatic. CECT abdomen and thorax revealed no residual tumor or lung metastasis. Histopathology was reviewed which showed follicular dendritic cell sarcoma [Figure 1a]. Mitotic rate was 10/10 hpf. On immunohistochemistry (IHC) it was positive for CD23 while negative for C kit, DOG1, AE1/AE3 and S100 [Figure 1b]. In view of high grade nature of the tumor the patient has been advised gemcitabine-Docetaxel-based chemotherapy.

Figure 1

(a) Histopathology showing follicular dendritic cell showing sarcomatous change. (b) On IHC, cells showing CD23 positivity

FDC sarcoma was first described by Monda et al. in 1986.[1] Follicular dendritic cells are found in primary and secondary follicles. They play an important role in antigen presentation for the B-cell compartment, as well as regulation of the germinal center reaction. Hence, these tumors arise from the lymph nodes in various parts of the body. Extranodal FDC sarcomas are rare and have been reported to arise from various sites in the body including such as head and neck, liver, spleen, gastrointestinal tract, soft tissue, skin, lung and breast.[2] More than one third of these tumors are initially misdiagnosed since IHC markers essential for their diagnosis are not routinely used. On histology, these tumors were composed of spindle arranged in sheets focally exhibiting a storiform or whorled growth pattern. On immunohistochemical testing, they stain positive for CD21, CD35 and CD23. There is no consensus on its management in view of its rarity though majority of these are treated by wide local excision followed by adjuvant therapy in the form of radiotherapy or chemotherapy.[3] Prognosis wise these are considered as intermediate grade sarcoma with a tendency to recurrence and development of distant metastasis.[4]

We are reporting this case in view of the rarity of this malignancy and the importance of IHC in the diagnosis of gastrointestinal malignancy to avoid inappropriate treatment practices.