Supplementary Material for: A 15-year-old boy with primary maxillary bone anaplastic lymphoma kinase-positive anaplastic large cell lymphoma relapsed with rib metastasis after spontaneous remission of a maxillary bone lesion: a case report and literature review

Anaplastic large cell lymphoma (ALCL) is a rare form of non-Hodgkin's lymphoma (NHL) in children, accounting for 10-15% of all NHL cases. ALCL is currently classified into categories of: 1) systemic anaplastic lymphoma kinase (ALK)-positive, 2) systemic ALK-negative, 3) primary cutaneous, and 4) breast implant-associated ALCL. In children, systemic ALK-positive ALCL is most common, and patients often present with extranodal involvement. We report a rare case of systemic ALK-positive ALCL with primary bone involvement in a 15-year-old male. Primary bone lymphoma is most commonly observed in diffuse large B-cell lymphoma, and is extremely rare in systemic ALCL. Therefore, the clinical features and prognosis of primary bone ALCL remain unclear. Our patient had spontaneous remission of primary maxillary bone ALCL after gingival scraping but relapsed one year later with rib metastasis. Spontaneous remission of ALCL has been reported more frequently in primary cutaneous ALCL and in a few cases in systemic ALCL, excluding primary bone ALCL. Our case demonstrates for the first time that systemic ALCL can also present as solitary bone involvement that can spontaneously remit. Because systemic ALCL is aggressive and has a risk of relapse, as in our case, it is important to consider ALCL in the differential diagnosis of primary bone lesions, and to make a precise pathological diagnosis.