Pediatric-type follicular lymphoma (PTFL) and pediatric nodal marginal zone lymphoma (PNMZL) are rare pediatric-type indolent B-cell lymphomas (PedIBCL) that differ clinicopathologically from their adult counterparts. Accurate diagnosis is important to avoid overtreatment but is often challenging. The mutational landscape of PTFL is known and may aid diagnosis, but the genetic features of PNMZL are not well understood. We analyzed 21 cases of PedIBCL according to their clinicopathologic findings and classified them into PTFL (n=11), PNMZL (n=2), and “mixed type” tumors (n=8) showing ambiguous histology. We also analyzed 2 cases of adult B-cell lymphomas showing features of PedIBCL. Targeted sequencing of 121 lymphoma-related genes was performed. The median age of PedIBCL patients was 16 years (range: 3 to 47), and all but 1 PTFL patient were male. All patients presented with limited-stage disease, and only 1 relapsed. There were no significant differences in clinical features among the 3 PedIBCL groups. The most frequently mutated genes were MAP2K1, TNFRSF14, KMT2C, IRF8, and NOTCH2. The genetic features of all groups were similar to the established mutational landscape of PTFL. The 2 adult B-cell lymphomas cases also had MAP2K1, TNFRSF14, and IRF8 mutations, but the clinical features were not typical of PedIBCL. In summary, this study demonstrated that PTFL and PNMZL are similar diseases with overlapping clinical, pathologic, and genetic features; mixed type tumors can also occur. Atypical adult cases with similar histologic features were also observed. Therefore, the disease spectrum of PedIBCL may be much broader than is currently believed.

小儿型滤泡性淋巴瘤 (PTFL) 和小儿淋巴结边缘区淋巴瘤 (PNMZL) 是罕见的小儿型惰性 B 细胞淋巴瘤 (PedIBCL)，其临床病理学不同于成人淋巴瘤。准确诊断对于避免过度治疗很重要，但通常具有挑战性。PTFL 的突变情况是已知的并且可能有助于诊断，但 PNMZL 的遗传特征尚不清楚。我们根据临床病理结果分析了 21 例 PedIBCL，并将其分为 PTFL（n=11）、PNMZL（n=2）和组织学不明确的“混合型”肿瘤（n=8）。我们还分析了 2 例显示 PedIBCL 特征的成人 B 细胞淋巴瘤。对 121 个淋巴瘤相关基因进行了靶向测序。PedIBCL 患者的中位年龄为 16 岁（范围：3 至 47 岁），除 1 名 PTFL 患者外均为男性。所有患者均表现为局限期疾病，仅 1 例复发。3 个 PedIBCL 组的临床特征无显着差异。最常发生突变的基因是MAP2K1、TNFRSF14、KMT2C、IRF8和NOTCH2。所有群体的遗传特征都与 PTFL 的既定突变景观相似。2例成人B细胞淋巴瘤也有MAP2K1、TNFRSF14和IRF8突变，但临床特征不典型PedIBCL。总之，本研究表明 PTFL 和 PNMZL 是相似的疾病，具有重叠的临床、病理和遗传特征；也可发生混合型肿瘤。还观察到具有相似组织学特征的非典型成人病例。因此，PedIBCL 的疾病谱可能比目前认为的要广泛得多。