Background: Young patients with papillary thyroid carcinoma (PTC) have generally excellent prognoses despite their often-advanced disease status. To clarify the natural history of PTC in children and adolescents, we compared the tumor volume-doubling rate (TV-DR) under observation with hypothetical tumor volume-doubling rate (hTV-DR) before presentation in young PTC patients. DR is a reciprocal of doubling time and indicates the number of doublings that occur in a unit time. A negative value means the number of halvings per unit time.
Methods: We enrolled 20 patients with PTC diagnosed cytologically aged 12–19 years who were followed with periodical ultrasound examinations for ≥3 months before surgery due to various reasons. Seventeen of them later underwent surgery confirming the diagnosis. We calculated the TV-DRs using tumor diameters measured serially after presentation. We also calculated hTV-DRs using the tumor diameters and the patient's age at presentation, assuming that a single cancer cell was present at the patient's birth and that the tumor grew at a constant rate. These values indicate the least growth rates necessary for a single cancer cell to become the tumor size at the presentation.
Results: Thirteen patients had positive TV-DRs (/year) ranging from 0.09–1.89 indicating slow growth, and the remaining seven patients had negative values (-0.08 – -1.21) indicating regression. The median TV-DR was 0.29. The hTV-DRs (1.53–2.72, median 1.71) were significantly larger than the TV-DRs (p<0.001), indicating much faster growth before presentation.
Conclusions: These data suggest that deceleration of tumor growth has already occurred at presentation in the majority of the cases. This might explain why disease-specific survival is excellent, despite the frequent advanced disease in pediatric/adolescent patients with PTC.