[Clinicopathological characteristics of pediatric-type follicular lymphomas: an analysis of 37 cases]

Objective: To study the clinicopathologic features, immunophenotype and prognosis of pediatric-type follicular lymphoma (PTFL). Methods: Thirty-seven cases of PTFL at the Beijing Friendship Hospital, Capital Medical University, from January 2012 to March 2018 were analyzed using light microscopy, immunohistochemistry, and polymerase chain reaction (PCR), and 13 cases were also examined using fluorescence in situ hybridization (FISH). Results: The male to female ratio was 35∶2. The median age was 16 years. Thirty-one patients were clinical stage Ⅰ and 6 were stage Ⅱ, displaying enlargement of lymph node in the head and neck regions. Follow-up information was available in 32 patients. Only two patients received low-dose chemotherapy, and none of these patients had relapse or disease progression at the latest follow-up (ranging from 16 to 79 months; median, 37 months). Morphologically, the lymph node architecture was partially or totally effaced by expansile follicles lacking polarization, with a prominent "starry sky" appearance. The cytologic composition was dominated by monotonous medium to large-sized blastoid cells with round to oval nuclei, finely clumped chromatin, small nucleoli, and scant cytoplasm. Immunophenotypically, all cases were positive for CD20, CD10, and bcl-6, but negative for bcl-2, MUM1 and C-MYC. Tumor cells were restricted to the follicles. The Ki-67 immunohistochemistry demonstrated a high proliferation (50% to 90%). Moreover, the tumor cells in the examined 28 cases were negative for CD43, CD5 and CD23. PCR analysis revealed monoclonal Ig gene rearrangements in all specimens. Thirteen cases being subjected to the FISH testing lacked bcl-2 and bcl-6 translocations. Conclusion: PTFL is different from conventional follicular lymphoma in their distinct morphology, immunophenotypic and molecular features, and behaves like an highly indolent or benign tumor.