Among 730 primary malignant cardiac tumor (PMCT) cases from the SEER-18 registry (2000–2021), two biologically distinct lineages emerged with sharply different clinical profiles. Soft-tissue PMCTs — dominated by hemangiosarcoma/angiosarcoma (43.9% of 458 cases) — skewed younger (ages 45–64) and underwent primary-site surgery in 66.6% of cases. Hematologic PMCTs — largely diffuse large B-cell lymphoma (61.8% of 212 cases) — clustered in patients ≥65 and rarely received surgery (15.6%). Most strikingly, hematologic patients who received chemotherapy achieved 42.0% unadjusted 120-month overall survival versus 12.2% without chemotherapy.
This preprint, not yet peer-reviewed, offers the largest systematic SEER-based comparison of PMCT subtypes to date, filling a meaningful gap given how rarely these tumors are encountered — estimated at under 0.1% of all cardiac masses. The chemotherapy survival signal in hematologic PMCTs aligns with broader evidence that cardiac lymphomas, like their nodal counterparts, respond to anthracycline-based regimens. However, the authors themselves caution that SEER captures registry coding, not treatment intent or protocol quality, and the chemotherapy variable is binary with unknown cases folded into the negative arm — a significant confounder. Survival analyses are unadjusted, and no multivariate modeling controls for stage, comorbidities, or era effects. For clinicians, the practical message is confirmatory rather than paradigm-shifting: PMCT subtype should drive treatment strategy, with systemic therapy central for cardiac lymphoma. Larger prospective registries with granular treatment data remain urgently needed.