A 53-year-old female with a history of HLA-B27 positive polyarthritis underwent a splenectomy due to an incidental splenic lesion, which was confirmed as an inflammatory pseudotumor (IPT). Afterwards, two liver lesions were found and histopathological examination revealed inflammatory pseudotumor-like follicular dendritic cell sarcoma (IPT-like FDCS). The patient received NSAIDs, corticosteroids, antibiotics and azathioprine, with no response. Within the next few months, there was an abrupt clinical worsening due to rapid progression of the hepatic lesions and a massive hepatomegaly. New biopsies were obtained, showing undifferentiated sarcoma. The patient started chemotherapy with doxorubicin and eventually died.