Abstract P050

VARIANT HISTOLOGY IN PEDIATRIC NLPBL: ADVERSE FEATURES MITIGATED BY R-CHOP, INCLUDING FEASIBLE EARLY-STAGE DE-ESCALATION

Background: Nodular lymphocyte-predominant B-cell lymphoma (NLPBL) is an uncommon subtype of pediatric Hodgkin-lymphoma comprising typical-histology (patterns A-B) and variant-histology (patterns C-F). Variant patterns have been linked to higher-risk features and increased relapse, but the optimal pediatric treatment approach, particularly the safety of de-escalation in early-stage disease, remains uncertain.

Methods: We retrospectively reviewed pediatric patients diagnosed with NLPBL at Children’s Cancer Hospital Egypt. Histology was classified as typical or variant, with variant subtypes recorded as patterns C-F. Survival outcomes were analyzed according to frontline treatment, with focused evaluation of early-stage patients managed with observation after complete resection (stage IA) or reduced-cycle R-CHOP for unresected stage I-II disease.

Results: Among 87 patients, variant histology was identified in 41 (47.1%). Variant histology was associated with less favorable presentation, including advanced stage (p=0.06), B symptoms (p=0.05), and extranodal disease, particularly bone marrow and bone involvement (p=0.01). Progression/relapse was more frequent in variant than typical histology (39.0% vs 15.2%, p=0.009), and variant subtypes C and D were associated with inferior event-free survival (EFS; p=0.05). Among patients with variant histology, 5-year EFS was 94.4% with R-CHOP versus 33.3% with ABVD. In the updated early-stage analysis, 7/12 completely resected stage IA patients managed with observation had variant histology, with relapse patterns comparable to typical histology. Among unresected stage I-II patients treated with 3-4 cycles of R-CHOP, variant histology was present in 20/39 (51.3%), with only 2 relapses. Within the R-CHOP-treated cohort, variant-histology did not significantly affect 5-year EFS, including in early-stage patients treated with fewer cycles.

Conclusion: Variant-histology identifies a biologically and clinically higher-risk subgroup of pediatric NLPBL. However, this adverse impact appears to be mitigated by R-CHOP, with excellent outcomes even in patients with variant histology. Our findings further suggest that risk-adapted de-escalation may be feasible in early-stage disease, including observation after complete resection and reduced-cycle R-CHOP for unresected stage I-II disease, without an apparent loss of efficacy. These findings support prospective multicenter validation of histology-guided, response-adapted strategies.