Bone metastasis of retinoblastoma five years after primary t
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Retinoblastoma (RB) is a rare malignancy but represents the most common intraocular malignant tumor in childhood. Most patients are younger than five years at initial diagnosis. Five year-overall survival is higher than 95% in developed countries, although RB is a lethal disease if left untreated. The tumor spread of RB is mostly confined to the ocular bulb or infrequently locally to intracranial sites. Distant metastases of retinoblastomas are exceedingly rare, but basically known also in developed countries.

An eight-year-old girl presented with tibial pain and bone lesion five years after multimodal treatment of bilateral retinoblastoma, initially clinically suspicious of osteomyelitis. Histopathological examination of a bone biopsy specimen revealed a highly proliferative small blue round cell tumor mimicking Ewing's sarcoma of bone. Immunohistochemistry confirmed the diagnosis of distant metastasis of the previous retinoblastoma. Other subsequent primary malignancies presenting as small blue round cell tumors, such as sarcomas or leukemia, were excluded by immunohistochemistry and molecular methods.

In countries with early diagnosis of retinoblastoma, distant metastases of retinoblastoma are extremely rare, whereas subsequent primary malignancies are common in survivors of heritable retinoblastoma. Immunohistochemistry and molecular pathology are essential components of the diagnostic pathway. In retinoblastoma patients, distant metastases including osseous lesions should be included in the differential diagnosis of small blue round cell tumors.