e23332 Background: Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare and aggressive hematologic cancer that often involves the skin, lymph nodes, and bone marrow with poor overall survival (OS). However, conditional survival (CS) is not well studied. Methods: This retrospective cohort study utilized 2 independent databases: the TriNetX database, a global electronic health records database, as well as the Surveillance, Epidemiology, and End Results (SEER) program. The TriNetX cohort included 110 adult patients with BPDCN after propensity-score matching who received either chemotherapy or tagraxofusp from 2000-2025. SEER data included 637 histologically confirmed BPDCN cases from 2001-2022, stratified by primary site (skin, lymph nodes, hematopoietic system). OS was determined by Kaplan-Meier analysis, and CS was calculated as survival in subsequent years conditional on prior survival. Results: After matching, mean age in the TriNetX cohort was 68.9 years, and most patients were male (82–86%). OS was higher with chemotherapy vs tagraxofusp, though not statistically significant. Three-year CS given 1-year survival was 59.2% for tagraxofusp and 62.0% for chemotherapy. A total of 637 patients diagnosed with BPDCN in the SEER 22 database were included, with the most common primary sites being lymph nodes (n = 312), the hematopoietic system (n = 163), and the skin (n = 92). OS declined steeply during the first 2 years after diagnosis with 2 year OS of 62.6% (95% CI: 58.7 – 66.6) followed by a slower decline to a 5 year OS of 54.0% (95% CI: 50.1 – 58.0). CS at 5-years improved with increasing time from diagnosis, both overall and among each primary site (see Table). Conclusions: Survival patterns in TriNetX suggest chemotherapy may show modestly improved OS compared to those treated with tagraxofusp, although sample size limits inference. Improvements were minimized when comparing CS. Across all sites in the SEER 22 analysis, BPDCN showed a pattern of high early mortality followed by markedly improved CS, suggesting that patients who survive the first 2-3 years may enter a lower risk phase with significantly better long-term prognosis. Subgroup differences were seen, with lymph node primary disease demonstrating higher survival probabilities. Our results highlight that patients with BPDCN who survive the initial high-risk period have a notably improved long-term outlook, which offers important prognostic evidence for counseling and treatment planning. 5-year conditional survival by years survived, SEER 22 (2001-2022), % (95% CI). Years Survived Overall (n = 637) Lymph Nodes (n = 312) Hematopoietic System (n = 163) Skin (n = 92) 0 54.0 (50.1 – 58.0) 60.7 (55.2 – 65.5) 44.7 (36.3 – 51.0) 34.7 (23.9 – 42.2) 1 72.8 (68.5 – 77.0) 77.3 (72.0 – 82.0) 67.4 (57.0 – 74.7) 49 (35.3 – 58.0) 2 86.3 (82.8 – 90.1) 87.9 (83.4 – 92.2) 83.2 (73.6 – 90.1) 68.5 (52.8 – 78.5) 3 92.4 (89.5 – 95.9) 95.7 (92.8 – 99.2) 87.2 (78.2 – 93.8) 72.0 (56.3 – 82.0)
Shirodkar et al. (Thu,) studied this question.