Micropapillary carcinoma: Description and rise in incidence in the French Marne-Ardennes thyroid cancer registry.

CONTEXT

Yearly incidence of thyroid cancer has nearly tripled in the past four decades, due to improvements in and better use of diagnostic procedures, enabling detection of smaller tumors, and notably micropapillary carcinoma (MPC: ≤10 mm).

OBJECTIVES

The aim of our study was to confirm increasing incidence, to describe the characteristics and circumstances of discovery, and to examine the reasons for this rise in incidence of MPCs, based on the French Marne-Ardennes registry for 1975-2014.

DESIGN

This was a retrospective observational cohort study.

RESULTS

Two thousand six hundred and seventy-one patients with thyroid cancer were included for the period 1975-2014, with 966 (36.2%) MPCs. The percentage increased from 18.9% for 1975-1984 to 45.1% for 2005-2014. Standardized incidence per 100,000 patient-years increased from 0.86 for 1975-1984 to 6.20 for 2005-2014. Incidence increase was higher in women (ranging from 1.15 to 8.91) than in men (from 0.20 to 2.54). Incidence increased more in ≥50 year-olds (from 0.41 to 4.21) than in <50 year-olds (from 0.45 to 1.99). Most MPCs (84.6%) were discovered incidentally on histology, and were mainly unifocal (79.4%). Incidental MPCs were smaller, affected older patients and were less multifocal than those suspected before surgery. MPCs were associated with excellent survival and low morbidity, with <1.9% progression.

CONCLUSION

The present study confirmed the large rise in incidence of MPCs reported elsewhere. Most MPCs were discovered incidentally on histological examination in the context of surgery for benign pathology. Changes in access to health care and in physicians' and pathologists' practices are likely explanations for our findings.