Inflammatory pseudotumor-like follicular dendritic cell tumor: an underdiagnosed neoplasia

Follicular dendritic cell (FDC) tumor is an uncommon neoplasm. It generally presents as a slow-growing, painless mass, without systemic symptoms. Histological features usually include low grade spindle cell proliferation. This tumor occurs primarily in lymph nodes, especially cervical and axillary, however, involvement of extranodal sites such as the tonsils, spleen, liver, and gastrointestinal tract has been reported. Inflammatory pseudotumor-like follicular dendritic cell tumor (IPT-like FDCT) is a rare, distinctive histological subtype of this low-grade malignant neoplasm, with consistent Epstein-Barr virus (EBV) association. The differential diagnosis with other fibro-inflammatory tumor proliferations, as inflammatory pseudotumor (IPT) and inflammatory myofibroblastic tumor (IMT), may be challenging. In the present article, two cases of IPT-like FDCT of the spleen are presented, with a broad overview of the literature: one 77-year-old male and one 70-year-old female. A large immunohistochemical panel should be used for diagnosis, as no single specific and totally sensitive markers are available, including markers for CD21, CD23, CD35, CNA42, and clusterin. Individual cases may express one or more of these markers, so that all of them should be investigated. In situ hybridization for EBV is constantly positive. Immunostaining for ALK should be negative, as it is present in roughly half of the cases of IMT. This panel should be used in combination of clinical, laboratory, and topographic evidences. Importantly, inclusion of this lesion as a possible option in clinical and pathological investigation represents the basis for a correct diagnosis.