Distant Cutaneous Metastasis of Chordoma: A Systematic Review and Individual-Participant-Data Meta-Analysis of 52 Cases, with an Illustrative Poorly Differentiated Index Case.

Chordoma is a rare notochordal malignancy of the axial skeleton, and distant cutaneous metastasis is among its rarest manifestations-an under-recognised mimic of benign and malignant skin tumours that often presents with an incomplete clinical history. We performed a systematic review and one-stage individual-participant-data (IPD) meta-analysis of all reported cases of distant cutaneous chordoma metastasis, following PRISMA 2020, and complemented it with an illustrative index case of cutaneous poorly differentiated chordoma in a young adult. Missing case-level data were handled by available-case analysis without imputation, with denominators reported throughout. Pooled prevalences were estimated by logistic-normal random-effects models (heterogeneity by I2); latency to cutaneous metastasis was modelled as a time-to-event outcome, and brachyury uptake over time by meta-regression. Forty reports (52 cases) were included; individual data were analysable in 43. Median age was 59 years (range, 2 months-88), male-to-female ratio 2.3:1, sacrococcygeal primary 74% (31/42) and median latency 4.0 years (synchronous to 15). Physaliphorous cells, myxoid stroma and vacuolated cytoplasm dominated, yet brachyury and SMARCB1/INI1 were documented in only 6/52 and 1/52 cases. Pooled prevalences were 74% (95% CI 59-85) for a sacrococcygeal primary, 70% (55-82) for male sex and 77% (62-87) for physaliphorous morphology, with no between-report heterogeneity (I2 = 0%)-expected when almost every report contributes one patient, so these values consolidate rather than extend the descriptive data. Patients younger than 40 years reached cutaneous metastasis far earlier (hazard ratio 17.2, 95% CI 4.7-62.9; p < 0.001), and brachyury use rose across eras (ρ = 0.43, p = 0.008). Distant cutaneous chordoma metastasis is a late event that usually signals disseminated disease and a limited life expectancy, commonly months to a few years. Its recognition rests on integrating morphology with nuclear brachyury and, in epithelioid or young presentations, SMARCB1/INI1. We provide a differential-diagnostic framework and algorithm, distinguishing cohort-supported findings from expert interpretation.