Case report: Delayed retinoblastoma relapse in a lymph node after 9 years of complete remission.

Retinoblastoma (RB) is the most common primary intraocular malignancy of childhood. Recurrence of RB often occurs within 6 months to 1 year after the end of treatment. Orbital tissue is the most common site of recurrence in children who have undergone enucleation; other sites include the central nervous system, bone, bone marrow, lymph nodes, and other organs. Here, we describe an adolescent girl who presented with RB recurrence and metastasis in a distant lymph node after 9 years of complete remission. The tumor was an incidental finding during a routine examination and was misdiagnosed as lymphadenitis. After histopathologic examination of an aspiration biopsy sample, the correct diagnosis of recurrent metastatic RB was made. Systemic chemotherapy and surgical excision were provided; the patient remained tumor-free during the 6-month follow-up period. RB often relapses within 1 year after treatment; orbital tissue is the most common site of recurrence. However, our patient's case was unique in terms of delayed relapse and the presence of a single metastatic site; these findings may provide new insights into the behavior of RB. Furthermore, this case report indicates the need for lifelong follow-up of children with RB. Oncologists should be vigilant when treating patients with a history of RB, because complete remission does not mean complete safety; long-term recurrence and metastasis may occur. Lifelong follow-up is necessary for children with RB. Complete remission might be achieved after active and standardized treatment.